Rear Diffuser

[90RS13]

Ok, there is a thread about diffusers, etc; already, but I don't wanna jack someone elses thread to talk about my product, so I made a new thread. Hope this doesn't cause any confusion.

Aurace Aero has decided to make a rear diffuser for the S-chassis'. The S13, prototype is in R&D and there are still small things being worked out. I need someone with an S14 (in NE AR) to see me, so that I can start the process for the S14. Anywho, I have some pics of the S13 piece.


The piece is a venturi'd center section, diffuser. They are aluminum, and weigh 4 lbs. That may sound like alot, but I wanted to be sure they would be strong, because they will be hanging off of the back of lowered S-chassis'. The production pieces will be powder-coated black, and have Aurace Aero badging.

http://i3.photobucket.com/albums/y77/MatthewWells/diffuser0.jpg
http://i3.photobucket.com/albums/y77/MatthewWells/diffuser1.jpg
http://i3.photobucket.com/albums/y77/MatthewWells/diffuser2.jpg
http://i3.photobucket.com/albums/y77/MatthewWells/diffuser3.jpg
http://i3.photobucket.com/albums/y77/MatthewWells/diffuser4.jpg
http://i3.photobucket.com/albums/y77/MatthewWells/diffuser5.jpg

You'll probably notice the aluminum sticks out like a sore thumb. That's one of the reasons they will be powder-coated. Price will be between $100-$120.

I wanted to show fellow Zilvians, so that I can get details ironed out. First and most important thing is mounting. You'll notice the diffuser is mounted to my car with zip-ties. No, it's not because I'm cheap. I know that many people may end up using them, so it makes since for me to do testing this way. Also, I prefer this mounting for this piece. The diffuser is mounting against the gas tank. I don't like the idea of something bolted on, that will be against the gas tank, and hanging, down and out of the back of your car. Zip-ties can break free if struck hard, potentialy saving your gas tank from being dented, gouged, etc. Bolts could be used though. The piece would bolt to the rear bumper (metal lip) and in the middle, up through the spare tire well, floor. In the zip-tie method, they go through hoes drilled in the bumper cover and then through the metal lip of the bumper support. Then towards the front tied around the center most strap for the gas tank. I need to see what most people would want. It can be made with holes predrilled for zip-ties, or with bolts and holes drilled for them. Either way, I will have good instructions for mounting, included. Another thing is the middle fins. They are stitch welded but if popular consensus doesn't like that, they can be full seams.

As the gas tank makes mounting any rear diffuser somewhat precarious, these will be sold "for track use only". At this point testing is still on-going, so I will keep you updated when anything new comes up. You can also email any questions to [email protected]

thanks,
Matt Wells
Aurace Aero

[CaoBoY]

that looks/is horrible.

[90RS13]

Can you elaborate more? "That is horrible" really doesn't help me much.

[seanc]

how much wind tunnel testing have you done to ensure proper flow and to make sure it is actually gonna help. any "professional" product secured by zip-ties is questionable at best.

[90RS13]

Like I said, testing is still on-going. About the zip-ties, I explained all about that, and if you would rather see this as a "bolt in" piece then just post that and it will be taken under advisement with everyone elses inputs.

[TheTimanator]

Can you elaborate more? "That is horrible" really doesn't help me much.
get it powder coated, figure out a better way to mount it and then mount it on a car that has some type of aero and you will probably get more interest.

Personally, I would never buy one but thats just me. What other products do you guys make?

[ThatGuy]

As I have stated in diffuser threads before, I doubt a diffuser that size would do much good. Last time I checked, cars that actually use these for something more then looks, have the diffuser as wide as, if not wider then the whole rear bumper. I would definitely like to see some wind tunnel or other test results that show this worth putting on an S-chassis.

[SilviaDriver]

simple as this, if ur car isnt super track only car, ull NEVER need a diffuser

[90RS13]

Ok, because there is some doubt as to if this will have any effect, I wanted to show an example. The below photo is of a rear center diffuser made by Varis, a very well respected diffuser company in Japan. It is very close to the size of my piece and uses the same venturi design as used by any rear diffuser maker.
http://i3.photobucket.com/albums/y77/MatthewWells/varisevounidiff.jpg

The below photo is of this piece on an Evo. Note the sides are not part of the kit.

http://i3.photobucket.com/albums/y77/MatthewWells/varisevounidiff1.jpg

If you look at time attack cars, many of them use center rear diffusers. One of the current magazines has as STI time attack car, with a similar Varis rear center diffuser with no side attachments. (They have been proven to aid when being the only rear piece) I'm not trying to disrespect anyone, but the basic design of the piece I made has been proven for many years. Please also keep in mind that I am still testing. I can't tell you how all the testing went, when it's still on-going.

Again, please don't take this as disrespect, I know I'm just having to explain/prove my product like any unknown business would. And for reference the Varis center section only is $600, but yes it is CF. The reason I went with aluminum was to make a product that most Zilvians could afford, because I don't see anyone making a rear diffuser for us for cheap.

-matt

[EchoOfSilence]

But do you see how it covers a bigger surface area than yours? The sides are pretty important too, that is if you care that much about this

[McRussellPants]

WTF?


A) That thing is too small and angled to do anything other than hook air under your car.

B) It doesn't extend under the car any, all that thing is doing is hanging back there, the air isnt flowing off of anything, and the angle of attack is so bad it would prolly just seperate anyway.

C) Then theres the fact that that car doesnt have any other sort of aerodynamics on it. That thing isn't gonna do shit with your car a foot off the ground and no bumper/side skirts on it.

D) Do you know what laminar flow is?

E) :bowrofl:

OMG, I just noticed the zipties. LOLOLOLOLOLOLOL


Go to book store > Buy Carrol Smith's "Racecar Engineering" > Delete this thread.

[chmercer]

ahahaha that thing is ass. try again please. that thing would just hook air and get ripped off on the highway.

if you want to make a diffuser

get a sheet of aluminum, skin the underside of the bumper from behind the wheels all the way back, THEN tig on your strakes. and rivet it onto the bumper. the more gaps you have between the body and the diffuser, the less its going to do.

[HyperTek]

Have them make a universal one, which is just alot wider and deeper then that.. so people can trim it to fit. Maybe exhuast to tow hook.. and more close fitting like everyone suggested..

maybe a reason varis and others go with cf is becuase cf would just break apart instead of aluminum ripping out/denting the gas pan.. but aluminum should just bend up.

Im not against the product, id like to see a more hardcore version produce, and taken everyone's suggestin/dislikes into consideration.

The demo car isnt too convincing, but im sure the point would be to show how much an improvement it would make to a stock vehicle..

[90RS13]

Ok, just have time for a quick reply so here goes. I guess the pictures are bad and don't show this well from what people have said. There is no gap between the front of the diffuser and the gas tank. As for length, longer is pointless, it's already flush with the gas tank which keeps extending in. I think some people are getting this confused with a full underbody panel type diffuser. This is just a center section like many other companies offer.

This thread is aggravating. I wanted to make something that the S-chassis that could be had for a reasonable price. I posted a prototype version, so that people could give suggestions etc. Almost all I've got is people flaming about anything they can think of that's wrong with it. I know I'm not a known business but I'm not even getting a chance to try. There's no, "maybe you should have it wider, I'd be more into that", or "I'd rather have a bolt-in system", but instead it's "that's %$#%, you're @#[email protected]#%". That is in no way helpful to me develpoing this. After more testing is done, Id be happy to go further into detail about it, and I have myself to blame for some of the confusion from not having a picture from directly under the car.

To sum up, if you have critisism, that's what I want to hear. But if you can't use respect or tact, please just don't post.

[blu808]

You should consider scrapping that thing, and making a more functional one.


Like all the way from the rear subframe back.

[90RS13]

HyperTek, first off thanks for the tone of your reply. The vehicle is my own. I didn't try to get a better car to show it off because this is not the final product I'm trying to sell. I am trying to take everyones responses in, and see what I can do. IT's as close fitting to the underside of the car as possible, it is flush with the gas tank at the front. I'm not sure what some pople think is going to make the air "hook". So far it's only been tested at about 85mph, but it was rock solid through out the run. I'll ty to get some better pictures of it from angles where you can tell where excactly it is, soon.

[90RS13]

So far Zilvians definantly want a larger piece. I would call it a full diffuser, but with so many different ways exhausts come out on our cars it will go from the passenger side to the exhaust. Please tell me what you think about that. Next, I need to address the issue of people wanting it to go farther in. Here are some more pictures, but it's getting dark and they are shadowy, so I'll try and describe.

http://i3.photobucket.com/albums/y77/MatthewWells/new1.jpg

and
http://i3.photobucket.com/albums/y77/MatthewWells/new2.jpg

Pictures are shadowy, but the diffuser is against the gas tank. There are no gaps between them.

Hopefully you can see better what I mean about the gas tank. The diffuser already ends up at the gas tank which is a nice flat bottom piece. Extending more forward in the car would mean wrapping under the gas tank, and lossing even more clearance. Someone said something about my car being 1ft off the ground. Well, at the jacking points it's 6" all around and at that height the fins at the front of the diffuser are 6" up. That's not that far for street driving especially considering most off you are lower than me.

This picture shows the line of how it meets the gas tank

http://i3.photobucket.com/albums/y77/MatthewWells/new3.jpg

Ok, so maybe this helps...hopefully. Anyway, keep making suggestions, so far I've decided it will be bolt-in, extend from far passenger side (past tow hook) to the exhaust.

[shift_s14]

that is awesome me and my bro have been wanting to make one for a while

[s14xman]

looks like an erector set under the car! like said before it needs to be full

[McRussellPants]

Pictures are shadowy, but the diffuser is against the gas tank. There are no gaps between them.

Hopefully you can see better what I mean about the gas tank. The diffuser already ends up at the gas tank which is a nice flat bottom piece. Extending more forward in the car would mean wrapping under the gas tank, and lossing even more clearance. Someone said something about my car being 1ft off the ground. Well, at the jacking points it's 6" all around and at that height the fins at the front of the diffuser are 6" up. That's not that far for street driving especially considering most off you are lower than me.



Dude, it doesn't matter. That thing is so useless its hilarious.


Its so obvious that you just looked at the Cyber Evo and went "awww JDM".



A) To make a diffuser work you need a full undertray. The air thats getting to that monstrosity is already so turbluent that all that thing is doing is hanging there.

B) Your car needs to be low, a diffuser doesn't work 9 miles off the ground, the entire point is to try and force a vacuum, which won't happen if its easy to pull air under and from the sides of the car.

C) There needs to be a smooth curve from the undertray too the angled diffuser. having a sharp angle like that will just seperate the air at speeds lower than when it looks.

D) The diffuser needs to be smooth, IE 50 zipties hanging off the face of where your trying to keep flow smooth isn't helping.

E) if you can hang it with zipties wouldn't that be your first clue that its not doing anything?


In conclusion, don't try and design a diffuser with no physics under your belt... I haven't taken any classses, this is all just the basic rudimentary stuff I gleaned off of "Engineer to win".

In Before you ignore all this becuase its longer than "zomg diffuser JDM"

[axiomatik]

To be honest, at that size, it looks a little silly. The overall geometry looks pretty good, but it should be 12-16" wider, and I would try to make it extend forward past the subframe and tie to the bellypan of the car. I'm sure that big gap where the subframe sits substantially disrupts the air flow under the car. For a diffuser to work most effectively, the air flow needs to be smooth (laminar). You may have to make it out of multiple pieces to be economical. Have cut outs for the diff and to allow for suspension travel. I wouldn't worry too much about exhaust clearance. If people are really interested in getting performance out of this piece, they should trim it to match their particular exhaust, all it takes is cardboard for a template and a jigsaw. And I would anodize it, instead of powdercoating, definitely black or some dark color. I would also suggest bevelling the fins a little, so that the bottom corners don't stick out so far.

[S14DB]

Needs to hug the fuel tank better.

[90RS13]

Trying not to get into arguments or pissing contest with anyone, so I'm not going to respond to most of that. I will discuss some things that a couple people seem to be confused on. You do not need a full undertray for a rear diffuser. If you did there wouldn't be companies that offer a rear diffuser only, for cars with underbody's at least as turbulent as the S-chassis. And there also wouldn't be pure race cars using rear diffusers with no undertray on said cars. In my reaserch for this I found many STI, EVO and GTR time attack cars with full rear diffusers, or just a rear center section, and none of them had a full undertray. People keep talking about needing to be low. All I can say is, the diffuser is the same distance from the ground as the jacking points. How far away the diffuser is from the road is dependant on how low the car is. I also would like for people to note that rear diffusers are mostly for straightening out the air flow exiting the car. Down-force does come into effect with venturi's create a low pressure zone, but the main focus is to straighten air flow.

I know I can't control how people post on this thread but derogatory comments don't help anything. I want to hear what people think, especially the "bad" stuff, so I can know what people would like different, but there is no need for the "flaming" kind of attitudes. I want to produce a low cost, nice product for S-chassis owners. If you want to contribute go ahead, but if you just want to flame and make fun of me and what I'm trying to do then just make a different thread for that.

-matt

p.s. About the zip-tie thing, first off it's not going to be that way on the production piece. Second, I can stand on the back of it without it coming off, so unless it produces over 175 lbs of downforce it won't be comin off.

[zero.counter]

It is a good attempt, but back to the drawing board it is for you. As stated before, it is too small and no long enough from front to back. One of the purposes is to lessen turbulence, but as small as the prototype is, it won't do much other than stick out. It needs to basically cover up the belly and draw any air away from the not so aerodynamically minded portions.

Forget what those who seem to be "dumb and dumber" said, and glean the good info from this thread. Wide and long, with better mounting points that are rounded and not causing more drag than necessary. This application could be usefull to those whom it may apply, ricer or not. Ultra-conservatives will not agree however. Hey Russell and Charlie, want to race my BMX?

[90RS13]

Ok so to sum up where I'm at..

1. It's going to be bolt in, with lowprofile rounded heads.

2. It's going to go from the far passenger side to the exhaust. (about 36" wide)

3.With regard to length.. wraping under the gas tank loses clearance and makes the design much more complex. I'm trying to keep price at a minimun so for now I'm trying to incorporate the gas tank as the "front".

Tomorrow, when there's light, I'll make a mock-up of a new design and post, then go from there.

So please if you're going to post about zip-ties, don't. It's bolt-in. If you're going to post about how skinny it is, don't. It's going to cover almost all the back. If you're going to post about length, that's cool, but see what you think about my new design first. Other than that just keep that comments coming.

-matt

[McRussellPants]

I know I can't control how people post on this thread but derogatory comments don't help anything. I want to hear what people think, especially the "bad" stuff, so I can know what people would like different, but there is no need for the "flaming" kind of attitudes. I want to produce a low cost, nice product for S-chassis owners. If you want to contribute go ahead, but if you just want to flame and make fun of me and what I'm trying to do then just make a different thread for that.



Quit trying to make it sound like I'm flaming you.


You have no fluid dynamics experience, no?

You've done nothing but ignore everyone who's told you the design is shit except to try and justify it with "some cookie cutter looks only JDM y0 diffusers do it this way."

Come back when you have a basic understanding of aerodynamics and how airflow works, once agian I'll suggest you start with Carrol Smith "Engineer to Win".

[zero.counter]

once agian I'll suggest you start with Carrol Smith "Engineer to Win".
I have to admit Rus, that is actually a good book. Albeit I only read the first 3 chapters and thumbed through the rest.

Here you go thread starter...
http://www.amazon.com/gp/product/0879381868/sr=8-1/qid=1145850515/ref=pd_bbs_1/102-5374707-4795325?%5Fencoding=UTF8

[mmdb]

Looks cool. Glad to see peope are taking aero more seriously. Is there one coming out for the s14?

[CaoBoY]

where is this 'diffuser' going to bolt onto if its all ziptied to the gas tank?instead of rounded heads on the screws why not just use flush screws? and i call bullshit on this whole '175 pounds of downforce' there's not even enough room to step on it, especially with the fact that its ziptied on there. and it looks stupid, like people cutting their rear bumpers with hole saws and thinking that it helps, when in all actuality it slows the car down. asthetically, that 'diffuser' looks like rice, like the 57ft long wings you see on civics nowadays.
it really just looks like you stuck that on there, and hoped people would love it. maybe it would look better on a car with full aero (which probably helps the air flow more than this) than a completely stock car with a horrible exhaust canister next to it. why not just scrap this? are you planning on making an actual race car out of your 240? are you actually going to do wind tunnel testing or even fluid dynamics testing to prove that this will actually help you? driving 1 time at 85 mph on the highway is not going to tell you if this 'diffuser' is functional to the car. if anything, just quit now, and wait til someone else makes it who has the time/money to invest in it.

[Wiisass]

I have a question about the testing. What are you testing and how are measuring it? Are you mearing pressure differences with and without the diffuser. I mean it's obvious that wind tunnel tests are definitely out of range financially, but do you have any solid data? I'm not attacking you, but this far it seems that you've only made it and attached it to the car and driven real fast with it and it didn't fall off.

If you haven't done any real testing, then what are your design assumptions behind all of this? Or is this a pure, this looks like it will work type of thing.

I also agree with whoever said it before, it's aluminum, so anodize it, not powdercoat.

[redsuns3838]

definately way too small for function. make it wider

[R33GTS-T]

subscribed:bow:

[90RS13]

Looks like the longer, and wider people will be happy..er. I started a new piece today, and at first was trying to make it wider but use the gas tank as a front section, so that it wouldn't have to be so low. Well, As I was working around the gas tank, the surface area of what would be the venturi'd section kept getting smaller and smaller. Finally I decided to ditch that idea. Now It's going to start right aft of the diff. It's going to go under and cover the entire gas tank. This is going to make it ride lower to the ground, which some might not like for street cars, but it's the only way I'll be satisfied.

When I first started this I tried to sacrifice some porformance for, more clearance, low cost to make, low cost to ship... but I'm now convinced that the people that will want a rear diffuser, will want the best functioning piece they can have, or nothing. I like that about the S-chassis crowd. Function first.

-matt

[lilredstiffy]

If only making money were as easy as ziptie-ing a piece of aluminum to a gas tank.

such a cruel world

[broken240sx]

A+++ for effort. I'm in the function crowd, not big on aesthetics, but if this thing works... I got $$$

keep at it, read up on race car engineering, McRussell may be a little caustic but he is right, Aero is difficult and costly to design effectively, it's the major difference between million dollar speed machines and anything modified to achieve speed.

this doesnt mean you can't provide the S-chassis with some worthwhile improvement, as it sucks now (in this department, of course)

good luck, keep posting pics

[CaoBoY]

WHAT ABOUT TESTING!?!
you driving around means squat to the rest of everyone here. no one cares how you feel it works. aurace aero is going to do testing or no? no matter how much you make it 'perform' without testing its still fashion over function with this piece.

[Saisoku]

Im part of the crowd here thats wants to hear more info on where you are getting the calculations for this piece. I do give you alot of respect for trying out a project like this. My main concern is, are you setting yourself up for failure. I personally have previously looked into diffuser technology, diffuser design and the associated mathmatics involved with all of them. I learned alot and most of that stuff my my brain bleed. Proper design of these pieces are nothing short of extrodinary. Those "side pieces" that you spoke about earlier in the thread are vortex generators and they have a lot to do with overall performance also. I wish you the best of luck with this, but there is one reason why I stopped doing the research. It was way too friggin hard. I am not a mathematician. I hope you have better luck with numbers than I do.

Oh and one last thing for you in case you didnt know. Diffusers in itself do not produce any downforce. It aids your spoiler in creating more downforce. Thats what my research has lead me to believe. So if you dont have a functional spoiler to begin with, you are just chasing your tail in the dark.

Again best of luck to you and project.

[Saisoku]

There were a couple of sites that helped me out big time, I will try to track them down for you and post them If I can find their addresses.

[yudalicious]

McRussell may be a little caustic
such an understatement, he's been a bigger asshole in this thread than a porn star's after an all night anal gang bang... at least most people are giving sound advice without the horrible attitude

[90RS13]

As far as testing, it will be done with wind testing (ribbon method) to see how air moves across the surfaces, of the rear, and pressure testing. If anyone wants more/different types done, I'll be happy to try something new. Right now testing has stopped though, because a new design is being developed. I never meant for anyone to think that the driving at 80 and standing on it were my forms of testing. Those were just rebutals to, "the wind will rip it off".

Ok, a new design, just working on basic areas for now. (no curves fins, etc). It's mounted for now, to the mounting points the gas tank cover bolt to.

http://i3.photobucket.com/albums/y77/MatthewWells/wood2.jpg

Here it's going under the gas tank. Ran out of the wood I was using to mock it up. It goes from exhaust to past the pass. side tow hook.

So I'd like to hear if people like the basic form of it so far. I don't want to keep working on this design if there are many objections to it.

-matt

EDIT- Also I may end up using composites for the final piece now, because it's going to use many mounting points on the gas tank.

[CaoBoY]

why dont you buy a HUGE sheet of sheetmetal. design it outta that. or cardboard, i dont think wood is good for a design. what do you mean by ribbon testing?

[90RS13]

The wood was already here and holds it's form well. I wasn't to worried about what I used because this is just to get the basic areas. Ribbon testing is a form of wind testing. It's kind of akin to fog-gun testing, but it focuses on the surfaces of the area tested. Basically strings are attached to the area and when wind passes over the area you can see the way the wind moves over the surface by watching the "ribbons". Usually it's done in a wind tunnel, but because my funds are limited, some gets to drive my car on the freeway like this,
http://i3.photobucket.com/albums/y77/MatthewWells/rear.jpg
while I follow behind and record speeds and video. It actually makes it very easy to see how the wind is moving.

[Ichi-Go]

What is your paypal... I am going to send you 25 grand to rent out a decent wind tunnel for a couple hours while you do a full scale mockup and test. I think that if you are trying to make a rear diffuser that is expensive and perfectly designed awesome becuase people in the 240 community understand how expensive R&D is. I am sure somebody will pay 2 grand for a rear diffuser after you make 5 or 6 prototypes. Also since it takes an entire undertray similar to whats on a Lotus Elise you should just sell the undertray too. Make sure you tig weld all the brackets and its made of carbon fiber nomex honeycomb. Also the string method of aerodynamic testing is crap olympic sailors dont use telltales and neither should you.

Like everybody says if you are trying something new, DONT you are a noob and aerodynamics are only for formula one cars. If it doesnt work perfectly its not work even trying.

[suprmods]

aerodynamics are only for formula one cars.


um, no. They apply to all cars.

To the OP, for the diffuser your two crowds are quite different. There are the people who want a diffuser for the race car look, and those that want it for the true performance benefits. Your design, whatever you come up with will most likely satisfy the first crowd and not the second.

The people that want a diffuser for its performance are those driving their cars on the race track, going speeds where aerodynamics is an important factor often over 85 mph (which makes testing for you on the street highly illegal). The tracks in southern california have low speed sections and high speed sections where even slow car (such as a modified civic/crx/integra) will reach 110 (buttonwillow) - 140 mph (willowsprings or cali speedway). Aero is an important part of how the car handles at that speed, for stability and grip. It is unlikely that these people are going to spend money on a part that has only been "freeway tested" and designed off of what people on zilvia want, and what a top Japanese diffuser looks like.

If you are still insistant in building this diffuser, it wouldnt hurt to just pick up one of the books mentioned above and read about aero and diffusers. At the very least you will learn something you may not already know, and it could improve your end product. Or just keep with the current design and testing techniques, get a part that fits nice, looks nice, and doesnt fall off at 85mph, and sell it for those aspects.

Good luck to you.

[R33GTS-T]

Looks like the longer, and wider people will be happy..er. I started a new piece today, and at first was trying to make it wider but use the gas tank as a front section, so that it wouldn't have to be so low. Well, As I was working around the gas tank, the surface area of what would be the venturi'd section kept getting smaller and smaller. Finally I decided to ditch that idea. Now It's going to start right aft of the diff. It's going to go under and cover the entire gas tank. This is going to make it ride lower to the ground, which some might not like for street cars, but it's the only way I'll be satisfied.
you may want to start with the venturi further under the chassis than in the original design

now that you are covering a larger area with a half belly pan you can start the venturi section further under the car and design them with a much more gradual incline from front to back....this should provide for a more effective smoothing of the airflow thus making the product more functional

personally, i road race and autox my car and i'm always interested in new functional aero parts coming out for the S chassis....so long as it has been sufficiently tested and proven to increase the car's road holding ability as high speed and so long as it does not increase drag or lift i would be interested in a product like this

- Daniel

[Ash]

What the fuck.....

[ThatGuy]

What the fuck.....

What a waste of your second post. If you don't plan on adding anything useful on Zilvia.net, feel free to Log Out and don't return. This is your warning.

[Cashizslick]

If you make one of these for an S14 and its not too pricey, ill buy it :)

http://img96.imageshack.us/img96/4343/mo5074img399x6001109923868demo.gif

[HaloZ]

What the fuck.....

2nd. a full tray is needed, not a regected desing for an f1 trophy.

[Wiisass]

As far as testing, it will be done with wind testing (ribbon method) to see how air moves across the surfaces, of the rear, and pressure testing.

Could you elaborate on the pressure testing you're doing or planning on doing?

[Nizzan4u2nv]

Could you elaborate on the pressure testing you're doing or planning on doing?

Did you read post #42?:tweak:

[Wiisass]

Yes i did, post #42 talks about ribbon testing which is not pressure testing. I'm talking about real pressure testing with some type of objective acquisition.

[90RS13]

Cashizslick, I'm focusing on the S13 until it's finished, but after that, the S14 is next. That particular style in the pic, has to be matched to a specific rear bumper. I'd rather not do anything matched to a certain bumper because that severely limits who can use it. I finished my wood stuff and now I'm doing a-full mock up with the correct radii, fins, etc; with 'glass. When it's done I'll post pics. As far as pressure testing, a range of speeds will be tested while measuring mm/Hg (millimeters/mercury) of vacume, at various points in the diffuser. I'll try to keep watching this thread and posting when there are questions/concerns, but I have alot of 'glass work to do still, and a chem final to study for. Again, thanks for comments and keep them coming.

-matt

[Cashizslick]

^ Why not make like the russians and copy what has already been done by other brands (for the S13)?

Just look at what they are making and find some way to make a universal fitting piece that all S13 owners can make fit their ride with little to no modification . .

Your first design was slightly promising . . . you should have just made it wider.

[Cashizslick]

oops x2 post

[R33GTS-T]

^ Why not make like the russians and copy what has already been done by other brands (for the S13)?

Just look at what they are making and find some way to make a universal fitting piece that all S13 owners can make fit their ride with little to no modification . .

Your first design was slightly promising . . . you should have just made it wider.
way to insult an entire race with a ridiculous blanket statement :tweak: :smash: :rant2:

[90RS13]

Just look at what they are making and find some way to make a universal fitting piece that all S13 owners can make fit their ride with little to no modification . .


I'm trying to finish the mock up as soon as possible, so you can see what the current design is. It will be a design that all S13's can bolt on, with little modification.

[Cashizslick]

way to insult an entire race with a ridiculous blanket statement :tweak: :smash: :rant2:

*** Soviets is what i shoulda said.

[reflexdb]

First off, let me make myself clear. I think that a functional rear diffuser for cheap is a great idea. If you could make something that performs (and provide testing results to prove it), looks decent, and is cheap, then I'm sure A LOT of people would buy it.

However, the first thing that you need to do is actually test it. For just a quick mock up test, I feel that the "ribbon" method is adequete. But, for final testing, that would not cut it for me. Definately I would think that pressure sensors at the least (tested on the car with, and without the diffuser) would be the minimum. I would actually like to see wind tunnel test results.

Secondly, someone was right on before when they said that 85 is probably not fast enough for a diffuser to do much of anything aerodynamically. Sure, F1 cars have them, but they also do well over 200mph down the straits. So...I have a feeling that even if you did make a very good product like this, it would be useless to the majority of people. Although, I'm sure that some people would buy it for looks.

Lastly, to make a solid design, you need to have a good amount of knowledge to base it off of. I don't know what your background is, but regardless of whether or not you have fluid dynamics experience or not, many have suggested good resources for information. For instance, the Carroll Smith books are a great place for info, but are a difficult read for people with little experience.

I would definately like to see a good finished product, so keep up the hard work.

[chmercer]

what is with you clowns and all this testing and shit. half of you probably roll around on 15s and mud and snow tires. you think autocross nationals, gt4, honda challenge etc wind tunnel test their shit? fuck no. drive a lap, write down time, rake the foil, write down time, tweak the shocks, write down time.

whoever is saying aerodynamics dont work at 85 or whatever, read a book. ever seen a stupid riced out civic with an aluminum wing with like 45 degree rake angle on the highway, stock suspension tucking rim? theres your answer.

props guy for actually making somthing, even if the first one kindof sucked. at least you are doing SOMTHING instead of watching f1 videos and dreaming about wind tunell testing an 80s passenger car like half the tools in this thread.

guy who posted top garage s14 - that diffuser is 100% show only. no performance benefits at all, that piece would make drag.

[REDSH!FT]

make it wide as the whole car...

instead of trying to make the whole thing mount up...make brackets up front for a LIP that will be flush w/ the bottom of hte car...flat...make it SEAL so no air gets by


then the rear have hangers (like an exhaust but use flat pieces of metal) with TABS that bolt to the underside of the trunk...Make sure this thing sticks out AT LEAST as far as an aftermarket exhaust tip


then you MIGHT have somethign that will work

[axiomatik]

I will suggest again that the diffuser extend forward to the floor pan of the passenger compartment to keep the air flow smooth. It can be made out of two pieces that butt against each other to keep costs down and still be shippable (or do a lap/half lap joint for more strength). You just need cutouts for the diff and to allow for suspension travel. Keep up the good work, and what chmercer said was right, how much test data do all the JDM tyte brands provide for their "aero"? :rolleyes: Track testing would be the most heplful. 99% of the people here wouldn't even know how to interpret the data if it was given to them.

[suprmods]

you think autocross nationals, gt4, honda challenge etc wind tunnel test their shit?

Quite the compelling argument, considering autocrossers will hardly EVER see 85 mph chasing cones in their parking lots. Gt4? Seems to me that is a video game, not to sure that any real testing was done car wise for that one. So for three of your examples, only 1 is a viable argument.

Honda Challenge is a series designed to keep the costs of racing low. If competitors started gaining access to wind tunnels and began testing their parts, its no longer cheap. PLUS, if you knew anything about the series you'd know that in 4 of the 6 classes rear diffusers are NOT ALLOWED.

But for your argument about wind tunnel testing, you are right. HC guys don't go out and hit the wind tunnel each month. nor do autocrossers, nor do gt4 bench racers.

This guys on the right path for wanting to do more testing, and thats all we are asking. Just don't drive on the freeway at 85mph, and since it doesnt rip off the car assume your good to go. More testing so people can see that this could be a viable product.

[R33GTS-T]

just found this over at First Molding's website
http://www.firstmolding.com/firstmolding/rear-diffuser/diffuser-canard-01.htm

scroll down to the bottom of the page for different angle pics
http://www.firstmolding.com/fm-aero/RPS13_180SX/180sx.htm

[McRussellPants]

Quite the compelling argument, considering autocrossers will hardly EVER see 85 mph chasing cones in their parking lots. Gt4? Seems to me that is a video game, not to sure that any real testing was done car wise for that one. So for three of your examples, only 1 is a viable argument.


:ugh: :ugh: http://www.freewebs.com/alms2006/links.htm :ugh: :ugh:


The reason GT4 cars don't need wind tunnel testing is they have a competent engineer on the job. Not to mention all the CAD programs availible to design it.


-Dude, you need this thing to at least have a partial tray. Trying to expand turbulent flow isn't gonna happen. At the bare minimum have it on the front subframe bolts.

-You won't record any meaningful pressure differences Vs. stock. To make this thing work you need a low front bumper and sideskirts. Racecars in the 80s didn't have the sides skirts and fronts interference fitted against the ground for shits and giggles. With the way it is now, its too easy to cancel the vacuum by pulling air from the front and sides of the car.

-a sharp edge to the diffuser won't work, air separation = turbulence = making it not work.

-Call me an asshole all you want. Just because I'm not on your nuts about "zomg diffuser that doens't work" doesn't make me any less right.

[CaoBoY]

i think he meant GT4 the game. haha
all those guys who want this diffuser made and are bitching about people crying about testing, you guys want it for what reason? to look cool? if you guys didnt care about testing why not just make your diffusers yourself? obviously its gonna be the same/cheaper to make it yourself. if you want a race product that actually works, then get a product that has been tested, and proven to help with aerodynamics in a good way, not just add drag.

[chmercer]

i think he meant GT4 the game. haha

Gt4? Seems to me that is a video game


seems to me you are both stupid kids?

why the hell would i bring up fucking video games in a thread about aerodynamics. is there anyone on this forum who isnt a complete retard.

here is a gt4 (SCCA CLASS NOT FUCKING PS2) car
http://www.race-cars.com/carsales/other/1128737584/1128737584ss.htm

it is a race car. 94 nationals. it has a wing. it has a front splitter. it has never been in a wind tunnel ever. it also has not been on the highway with bits of string on it.

here is some more
http://www.deepthrottle.com/Photo/run03_gt4_duo.jpg

i bet that front spoiler dosent work, because that civic has never been "tested" or whatever the hell that means.

what the hell does honda challenge being cheap have to do with the fact that their aero mods are track driven only. if you took the front spoiler/trays off half of thoes cars, they would loose a nice chunk off their lap times.

again. who cares how fast autocross cars go. they have aero mods. you completly miss the point.

ALL IM SAYING is dont waste time trying to tape string to your car and crap to test it, just read an engineering book (or read what myself and russell have been posting, and some others) and modify it as such

the problem with the underpanel aero mods which everybody so desperatley wants to run because spoilers are "ricey" (except the little fiberglass ones that are only for looks, thoes arent "ricey") is that they physically do not fucntion unless the car is extremely close to the ground, which not many cars in here are. and not "oh my ride is slammed" we are talking 1-2 inches panel to road clearance.

another picture
http://datsun_510.at.infoseek.co.jp/510jungle/nismo/00slet.jpg
this car was designed in the 80s, its a totally stupid design. look at it, its a rolling brick. it made tons of drag. but it also made tons of downforce. this wasnt as much of a problem when you could just put some 500 horsepower firebreather in and not worry about drag, but the point stands that basic aerodynamic principles can be applied with minimal testing and still be effective.

[suprmods]

why the hell would i bring up fucking video games in a thread about aerodynamics.

I've seen some crazy responses since being on Zilvia, gotta cover all the bases. After I posted I realized there is most likely a GT4 class elsewhere, so it was my mistake.

I never said anything about honda challenge cars not needing aero, or anything of the like. I brought up the supposed "cheapness" of the series to say that windtunnel testing is not as widely used, nor necessary as some people would like to think. Its not like anyone can walk up to a wind tunnel and say "hey I wanna test this part I made." I'm not sure everyone realizes that.

[chmercer]

haha allright then. my honda challenge example was only to cite an example of people using un "tested" aero products to an effective end.

[tre]

This is cool and all. But thers one main problem with making a rear diffuser for this car. Its not flat bottomed.

[tastyratz]

I have made several posts on underbody aero which can probabbly contribute if people search and read them. Problem with underbody aero is it is one of the more widely underestimated concepts. You do not have to be 1 inch from the ground to make a difference, but you most certainly will not get the same benefit mounting all the crap to an f350.
That small piece in the original design pictures I dont believe will do enough of a benefit. What you should do is make a piece that goes as wide as the back of the car leaving extra sheet by the exhaust, then people can trim it off appropriate to thier cars setup. If you can find a way to smooth out alot of the underbody confusion on the rear bottom it will definitely benefit. Personally because of the nature of the part i have a huge sheet of aluminum im going to rivet to my kit rear bumper, im then going to screw in lawn edging in a venturi tunnel design, then trim the bottom slightly. Yea its cheap and I dont care, it WILL be functional (wind tunnel testing may help me make a piece with 100% functionality, but im sure I can make a piece 75% that using basic principles like people were saying)
Using the lawn edging allows me to run the diffuser closer to the ground without being worried. Why? Stuff is like 10 bucks a roll, ill run it almost touching the ground and it will drag and beat to crap all the time. Eventually when I wear all the plastic through and down I can easily replace the fins with more 10$ plastic.

[Omarius Maximus]

I don't understand why you people are flaming the one person who has enough initiative to build something cool for your car. He doesn't need to have a formal education, and read up on a couple of books to make a product that works. My 2 cents; instead of pressure testing and all the that b.s. why don't you just do a top gear roll on? Go from like 100 to 120 and take note of the time. Then do it again with the diffusor and see if its changed the time. You should be slightly faster considering the simple fact that your eliminating the drag from the rear bumper.

[lilredstiffy]

Or would it be slightly slower from the production of more downforce?

[Ichi-Go]

I know I might get flamed for this but isnt the point of a rear diffuser not to produce downforce but to assist the rest of the car into producing downforce and helping to reduce drag. In a totally flat bottumed car the air under the car is accelerated creating a low pressure. At the back of the car you do not want the air jetting out 2 inches off the ground into a huge vacuum becuase it would slow the air coming out and make a bunch of drag and turbulance off the back of the car. The rear diffuser is made to slow the air down without flow seperation and also without any turbulance. The vertical stakes keep the air flowing straight and smooth and the raked design slows the air down to reduce the drag at the back bumper.

If I am totally wrong please correct me. Front undertrays would create more downforce than a rear diffuser. Then just slap a big GT wing on the back to even it out and there you go, effective downforce.

[axiomatik]

there seems to be a lot of confusion as to what diffusers do and how they work. the purpose of a diffuser is to create downforce with out increasing drag. spoilers increase downforce, but they are also like a big sail in the wind, and create a lot of drag as well. diffusers create downforce in two ways. first by accelerating the air under the car, pressure decreases with increasing velocity in a fluid flow. secondly, as the diffuser angles up at the back of the car, the air that was squeezed under the car now has much more volume to spread out into, further reducing pressure. the air above the car is still at normal atmospheric pressure, and the pressure below the car is now lower. this pressure differential pushes the car down much like an upside-down airplane wing while adding little additional drag. for a diffuser to work, it is important for the bottom of the car to be as flat as possible, which is why i keep suggesting that the diffuser be extended forward to the floorpan ahead of the sub-frame. if the flow under the car is very turbulent, it will be slowed down, create backpressure, and not produce any downforce. it is not necessary for the car to be slammed within 1" of the ground. this will inprove its performance, but it is not necessary to achieve benefits. the ferrari f430 uses a flat undertray with a diffuser, and it comes from the factory a lot higher off the ground than many cars here on zilvia. does that mean that is doesn't do anything? no, it just doesn't provide as much downforce as it would if it was lower.

[McRussellPants]

there seems to be a lot of confusion as to what diffusers do and how they work. the purpose of a diffuser is to create downforce with out increasing drag. spoilers increase downforce, but they are also like a big sail in the wind, and create a lot of drag as well. diffusers create downforce in two ways. first by accelerating the air under the car, pressure decreases with increasing velocity in a fluid flow. secondly, as the diffuser angles up at the back of the car, the air that was squeezed under the car now has much more volume to spread out into, further reducing pressure. the air above the car is still at normal atmospheric pressure, and the pressure below the car is now lower. this pressure differential pushes the car down much like an upside-down airplane wing while adding little additional drag. for a diffuser to work, it is important for the bottom of the car to be as flat as possible, which is why i keep suggesting that the diffuser be extended forward to the floorpan ahead of the sub-frame. if the flow under the car is very turbulent, it will be slowed down, create backpressure, and not produce any downforce. it is not necessary for the car to be slammed within 1" of the ground. this will inprove its performance, but it is not necessary to achieve benefits. the ferrari f430 uses a flat undertray with a diffuser, and it comes from the factory a lot higher off the ground than many cars here on zilvia. does that mean that is doesn't do anything? no, it just doesn't provide as much downforce as it would if it was lower.


Qouted for troof!

[tastyratz]

absolutely best way to explain.

People wonder why we get such crappy ideas and parts produced, its because when someone looks for feedback or attempts to build a part quality they get torn to shreds.

its easy to measure the cars drag. Omarius had the right idea backwards.
accelerate until 120, put the clutch in and the only force resistance is the wind. Use a stopwatch to see how long it takes for the car to go down to 85-90mph. Do this on a clear non windy day, and make sure all runs are on similar road conditions with the same car, same amount of gas in the tank, etc. Average out the times of several runs and you have a number that can actually mathematically be transformed to the cars CD if you can plug it all in. Do the same thing with the diffuser plate on and you will see the change.
This only exists with drag changes and WONT reflect CD. The only thing I could possibly imagine you could use to measure that would maybe be some sort of digital distance measuring device like a golf related tool or laser construction thing or something mounted to the trunk. This way if the car is pushed down an inch it will be reflected in the readings, so on and so forth.


I still think work on making a larger cut to fit part that concentrates on making the underbody flat, then add the fins to it after. Those things are trite in beta form.

[Wiisass]

That wouldn't work because you wouldn't be accounting for the friction on all of the drivetrain parts. Even with the clutch in the bearings and brakes and rolling resistance of the tires contribute to the car slowing down.

About the need for some kind of testing. If someone is going to try and market a functional part, they need to be able to back it up with at least principles and hand calcs, testing adds to this and makes the product look like a much better idea. Anyone can make something that looks like a diffuser and sell it as a "diffuser" but when you cross the line and say it's going to be functional, it actually needs to be.

If you're making something for your own car, or just trying something then who cares if you do any testing. I made a splitter for the front of my car, haven't messed around with it yet, but I just made a big piece that I can attach to the front bumper. I'll put it on and see if it works, but if I were to try and make more and sell it, I would have some test data to prove that it does more than just look cool.

[Omarius Maximus]

tastyratz is right on the money. AND his idea would work because the friction from the driveline is a CONSTANT for the most part. The only thing your changing on the car between runs is the diffusor, so his idea is probably the best way of figuring out whether it works or not.

We know that a dyno isn't exactly the most accurate way of measuring engine power, but we use it anyway to get a general idea of where we stand with modifications. The same would hold true for this method.

[Wiisass]

If you're trying to calculate a drag coefficient that way, you're going to be way off. If you're trying to compare a car with an aero part versus the same exact car without then it could work. You'll be able to get some comparison data, but nothing absolute.

If you really wanted to get good data you would test the part at an autocross or track day. The benefits of aero will be seen in the corners and not on the straights. Of course this applies to our cars, I'm not saying that cars don't need aero to help with high speed straight line stability, but the main benefit will be during cornering. You're hoping to achieve higher speeds throughout the corners because of the added weight on the tires from the downforce.

So go to an autocross or track day and run with the piece and without. Have people timing seperate sections of the course as well as your overall laptimes. Have someone else taking notes on what you feel, like does the car get loose or tight and where and why it's doing this. A radar gun would also be a nice thing to have in this case, so you could clock your entry speeds to different turns.

If you can do this and show and improvement just because of the addition of an aero piece, then that's good test data. Just keep in mind, that you need a good driver who knows what the car is doing and can turn consistent times on the course if you weren't to change anything. And if you want the most objective responses from the driver, don't tell him what you're doing.

[tre]

No ones flaming. Its a cool Idea but he needs todo far more than just that rear diffuser to show a noticable difference.

He needs to somehow pretty much cover up the rear end of the car (make it flat bottomed) that disturbs pretty much ALL air flow undernearth the car right there eliminating any use for a rear diffuser.

One cool thing i've seen but RARELY done and i do mean RARELY done.

Is the venturi tunnel through out the whole underbody of the car.

But anyways a simple thing to start the process of better downforce and creating a low pressure zone underneath your car. Would be to prop up the back of the hood an inch or two to let out hot air/pressured air in the engine bay compartment.

[tastyratz]

Wissas: Thats what I meant with the math- all those things can be plugged into a formula (if you didnt have stock cd). Technically we already know the stock aero CD so if you can aquire the correct math you can plug it into a formula and find the CHANGE in cd. This will tell us the actual effect.

Tre you do actually hold a point with the raised or vented hood however it would need to be coupled with a more sealing underengine splash shield panel. This would make the air have a harder time escaping under the car and also give it an alternative path for flow. That could work great and also backfire because the air will slow down, gain turbulence, and likely create a pocket right before the windshield actually hurting the cars drag...

This actually raises a good point now that I think of it though. I am willing to bet the air from the radiator going around the engine and all the other crap there is not exiting below the vehicle in a laminar fasion. Perhaps some sort of diffuser/splitter would be beneficial directly behind the engine bay as well.
You dont always really need something that goes the entire length of the car, but some fins behind the engine bay, and at the rear bumper area would be a consideration...

[90RS13]

I was busy yesterday and didn't get to do much but I made a cardboard piece and started to 'glass it. I did a layer on the top and the cardboard started warping so I just decided to make the real heavy wood piece that I'll make a mold from. In the pictures below, the center section is the only thing there. There will also be a flat piece covering the pass. side completely.

http://i3.photobucket.com/albums/y77/MatthewWells/cardboard1.jpg
^this is about as wide as the "active" section can be, due to different exhausts people may use including oem, cust, etc.

http://i3.photobucket.com/albums/y77/MatthewWells/cardboard2.jpg
^trying to show the clearance between the diffuser and the gas tank. There's about a half an inch.

http://i3.photobucket.com/albums/y77/MatthewWells/cardboard3.jpg
^This is for comparison. That's the first peice beside it.

As far as tying it into the "belly pan". The S13 doesn't have a good belly pan. Even in the center of the car where there's no suspension components, It's all humps, bumps, fram rails, etc. Doing this projest really has made me realize how little thought in aerodynamics, was put into the design of the S13's underbody.

A word on flat bottoms. Yes it would be nice and more effective at keeping airflow less turbulent, to have a flat bottom. But besides the airflow being less turbulent entering the diffuser, a flat bottom won't do alot. The only way a flat bottom will create lower pressure is if the car is raked, and there are deep side skirts that aren't raked. A flat bottom in and of it's self won't create lower pressure zones. The venturi tunnel someone mentioned is how many race cars get very low pressures under there cars. The basic design is like..front _/------\/ back. Thre's basically a "scooped" section under the car. This creates the low-pressure zones. The diffusers these cars use help magnify the downforce of the venturi tunnel by the fact that the air is rushed out of the diffuser, pulling more air out of the underbody. These applications do need deep side skirts, etc. The focus on touring car diffusers is different. It's not to aid the underbody venturi, but instead to provide benifits on it's own. These include lower-pressure in the diffuser, and straightening out airflow exiting the rear. A flat underbody will help keep air less turbulent, but a diffuser can function without it.

-matt

[90RS13]

But anyways a simple thing to start the process of better downforce and creating a low pressure zone underneath your car. Would be to prop up the back of the hood an inch or two to let out hot air/pressured air in the engine bay compartment.


Close, but a better way is with louvers. A louvered surface will pull air from the other side of the surface without badly disrupting airflow over the surface. That's why you see them used alot of times, in GT cars, on the surface above the wheels, so the air traveling above the wheel well, will pull air from inside the wheel well, which is important, because that is an area where air can easily become turbulent. Also in GT cars, (like JGTC) you see louvered hoods alot.

[tre]

Venting the hood wouldn't create a low pressure zone. The low pressure zone that can be created by the hood/winshield collide seems to be mainly present if the angle is lesser. IE VW Rabbit vs my 240sx fb. The rabbit would have a lower pressure zone instead of mine because i have a greater angle from hood/winshield. And raising the rear of the hood would make the angle even greater causing the air to stream better.

And hot air rises, correct? I think the pressurized/hot air would especape through that rear vent aswell. Causing that hood/windshield low pressure zone to raise in pressure due to the engine bay venting to it.

[jetblackskye]

lol, this is a very entertaining thread.

Okay so what if some one built a 'diffuser' and for looks and sold it. It would be sorta functional, right? But there would be no real hard core evidence. would some of you guys still buy it?

How many of you guys have big spoilers on your cars, or have friends that have them? Did they ever call up APC and say, "hey how much down force does this spoiler produce at 75 mph with a 31 degree tilt? 85mph? 150mph? What about the coeficient of drag?" Do you even know your stock CD? And what does it mean to you if it changes?

Everything makes aero variable, have you ever seen Bernulli's equation? I mean the full version that takes into account the difference in not only pressure, but temperature, velocity, viscosity, etc, etc.

Most race cars are simply tested as was said earlier, drive a round a track as fast as you can, and then do it again and change something. If it worked cool, if not try something else. Even the guys at nascar do this and they have the millions of dollars of backing.
Real world testing is the most variable but also the most conclusive.

I've had an unfortunate event happen recently and I've had to pospone my project, but I'll be back up and ready in a few weeks.



90RS13, Mad props for making a diffuser. I'm your competion, hagimemashte.

[tre]

lol. actually one of the best fake wind tunnels. Dad and other racers have done this. Sounds hilarious and looks it to especially when you do it on the freeay.

Cut an inch or more of sring and place it equal distants apart from each other in a grid pattern. across your whole car. It'll show the wind currents traveling across your car.

[McRussellPants]

A word on flat bottoms. Yes it would be nice and more effective at keeping airflow less turbulent, to have a flat bottom. But besides the airflow being less turbulent entering the diffuser, a flat bottom won't do alot. The only way a flat bottom will create lower pressure is if the car is raked, and there are deep side skirts that aren't raked. A flat bottom in and of it's self won't create lower pressure zones. The venturi tunnel someone mentioned is how many race cars get very low pressures under there cars. The basic design is like..front _/------\/ back. Thre's basically a "scooped" section under the car. This creates the low-pressure zones. The diffusers these cars use help magnify the downforce of the venturi tunnel by the fact that the air is rushed out of the diffuser, pulling more air out of the underbody. These applications do need deep side skirts, etc. The focus on touring car diffusers is different. It's not to aid the underbody venturi, but instead to provide benifits on it's own. These include lower-pressure in the diffuser, and straightening out airflow exiting the rear. A flat underbody will help keep air less turbulent, but a diffuser can function without it.

-matt

Go Read a book. / If you think turbulent flow upstream of a diffuser doesnt matter you don't need to be making diffusers.

[90RS13]

If you think turbulent flow upstream of a diffuser doesnt matter you don't need to be making diffusers

I didn't say turbulent flow upstream doesn't matter. I said, (in regards to a flat bottom) that it can function without it.

[tre]

So i'm curious to why we're bickering about this when all this stuff that we're discussing when we'd never see a difference in downforce. How many of you are actually going out to the track and doing 60+ throughout the whole track (where'd you'd probably notice any gain with a diffuser)

Me. I'm staying away form downforce. Gravity is already against me in the events I do.

Plus you'd want to somehow make more downforce on the front if you're going to use a rear diffuser for the fact that you dont want an unballanced car. You dont want a bunch of downforce in the rear without balancing it in the front aswell. Or you'll just end up pushing!

But then again with how much actually downforce that will be generated i dont think it'll matter lol

thats my .02 cents on the matter now :P

[90RS13]

So i'm curious to why we're bickering about this when all this stuff that we're discussing when we'd never see a difference in downforce. How many of you are actually going out to the track and doing 60+ throughout the whole track (where'd you'd probably notice any gain with a diffuser)

Me. I'm staying away form downforce. Gravity is already against me in the events I do.

Plus you'd want to somehow make more downforce on the front if you're going to use a rear diffuser for the fact that you dont want an unballanced car. You dont want a bunch of downforce in the rear without balancing it in the front aswell. Or you'll just end up pushing!

But then again with how much actually downforce that will be generated i dont think it'll matter lol

thats my .02 cents on the matter now :P

I know the downforce/low-pressure crap is mostly what's being talked about, but that's not the main purpose of a rear diffuser on street cars. The main purpose is to straighten airflow, and lower drag and turbulence. That's why alot rear diffusers made for street cars, aren't much more than a flat panel. There are different designs/approaches, but in general a rear diffuser made for a street car/autocross/lower speed etc, is made to give the car less drag.

[tre]

I know the downforce/low-pressure crap is mostly what's being talked about, but that's not the main purpose of a rear diffuser on street cars. The main purpose is to straighten airflow, and lower drag and turbulence. That's why alot rear diffusers made for street cars, aren't much more than a flat panel. There are different designs/approaches, but in general a rear diffuser made for a street car/autocross/lower speed etc, is made to give the car less drag.


I'm just curious who actually has noticed a difference though?

Can we get a product test going? lol

[R33GTS-T]

for those of you who know about air flow characteristics....

would it be beneficial to have a completely flat belly pan made up....front the front bumper to the rear....wouldn't that alleviate any issues that may arise from turbulent flow under the car? or would that create issues at high speeds w/o any additional aero pieces added to the car???

[tre]

for those of you who know about air flow characteristics....

would it be beneficial to have a completely flat belly pan made up....front the front bumper to the rear....wouldn't that alleviate any issues that may arise from turbulent flow under the car? or would that create issues at high speeds w/o any additional aero pieces added to the car???


If you make the whole car flat bottomed it would be good. but have fun doing that :)

I'd like tos ee what you can come up with though ^_^

[R33GTS-T]

If you make the whole car flat bottomed it would be good. but have fun doing that :)

I'd like tos ee what you can come up with though ^_^
i've been thinking about this for a while now......might take up this project this season

[tastyratz]

Making the whole underbelly flat in our car by adding a big sheet panel will probabbly be more weight than the tradeoff is worth. The main points of address are from the subframe area back, and the under area by the engine bay. The center of the car isnt THAT bad.

90rs13:
Yes a diffuser can function without it, I can eat cereal with my fingers but it doesnt mean its going to efficiently produce my end goal (which is cereal in my mout with minimal milk on shirt co-efficient)

reducing underbody turbulance (which im sure we are loaded with) will reduce overall car drag, will produce higher air speeds, and be more likely to produce an underbody vacuum. Technically you want whatever air under the car traveling faster than the air above it so it literally sucks the car down. Diffuser will air in high speed stability, and help with downforce (or actually I should say in this equation reduce lift- you wont ACTUALLY be producing downforce its just easier to refer to as downforce)
All factors should be considered.

Considering your questioning opinions on a product your going to sell, You might want to build it around what the buying public wants.

[90RS13]

You might want to build it around what the buying public wants.
So true, and alot of people want more coverage. I threw up some cardboard going further forward.

http://i3.photobucket.com/albums/y77/MatthewWells/tray1.jpg

^here's a shot down the car with no fins, so you can see better. The section rear of the suspension will be wider, this was just to show how far forward it would go.

http://i3.photobucket.com/albums/y77/MatthewWells/tray2.jpg

^Meets up with the "belly pan".

So, please post up and tell me if you like how far back it goes. The more people post and give opinions, the quicker I can make changes and get closer to the final design.

-matt

[tastyratz]

coverage is definitely looking more acceptable and definitely more along the lines of what I would buy if I were in the market for it.
Where it meets with the frame rails does it have a big gap in the center or does it have a fold that extends to the full belly pan above the frame rails so you dont just have a big shovel under the car?
You may want to also consider making the end product out of a metal like sheet aluminum thats light and will take impact (unlike fiberglass)
as well as for the fins do something like im doing or just get plastic ones made. This way you can extend down lower to the ground without worrying about clearance as much (who cares if it scrapes? it can become a wear part)

[Kinematics]

Zilvia: Where everyone is an expert. :ghey:

edit: I'll add something useful.

I like this product, would like to see it implemented on an S14. I however would like to see some actual benefit of this. Perhaps finalize a design and sell a copy to someone who actually races their car, and get a review on the performance.

I am not much into drifting, mostly hillclimb events and road racing, so if there is a benefit in this product I would take serious consideration into purchasing one for my S14.

[tre]

you could probably use the exhaust hanger right infront of the driver side rear fender as a place to bolt it up possibly as well. but make sure you can make it so its easially accessable to remove. I hate pain in the ass uninstall jobs haha :P

[Slidin240Wayz]

What about extending it to the bottom of the rear quarter panels?

[90RS13]

What about extending it to the bottom of the rear quarter panels?

The last post I made was just to show how far forward it would go. People seem to like that, so now I'll start seeing how much coverage I can get without interfering with suspension, and also start looking at what mounting points to use. I think it is going to be necessary to drill at least two holes through the "bellypan". I'll try and use as many stock bolts as possible, but we'll see how it goes. The exhaust is going to be the big issue. Different exhausts vary in angle, etc. It's already going to be in 2 "halves" divided by the exhaust, but the space in between for the exhaust may have to be wider to accomadate different exhaust types. I know some people are going to say to just leave it whole and let people trim, but most people don't have sheers and these panels will be a little on the thicker side (being close to the ground and all). And the material is diffenantly going to be aluminum, (don't want a large composite panel under the car).

Oh, and what do people think about the diff? I was going to have it covered, (it's covered in the picture), but then I remembered when I was in Germany, the Euro-spec S13's had diff coolers, so heat must be somewhat of an issue at high speeds, so I think I will have a cut-out for the diff as well. Maybe just the bottom half of the diff sticking through...

as always please reply.

-matt

[JohnC]

Here are pics of a diffuser on an s14

http://192.115.8.73/Images/Nissan/hispee2.jpg

http://192.115.8.73/Images/Nissan/hispee1.jpg

I will buy it and try it.

John

[R33GTS-T]

If you fab one up out of aluminum and need some real world testing done.....if you'd like I can test it out for you on some of the road courses I plan on running at this season (i'm only in philly too ;) )

as for the diff.....i would leave more room than just the bottom half for the diff to receive air for cooling purposes....the last thing anybody wants is to overheat their diff at the track :ugh:

if you make the front "half" of this piece either bolt in or riveted in i think that would be fine (personally i wouldn't have a problem riveting it into place...less likely to rattle and vibrate the bolts loose) and the rear section i think you should allow for some minor trimming so that the design will provide the largest coverage area but for the people with angled exhausts, they can just trim as they'd like and the people without angled exhausts won't have to suffer and lose coverage area :bigok:

is it possible for the width in the rear to cover beyond the tow hook? it looks to me like that exposed area could still cause some turbulence thus negating the benefits of smoothing out the airflow prior to that point

where the two pieces meet up you may want to design them with a tapered design so that the rear of the front pieces goes below the front of the rear piece and they overlap....preventing air from getting in between the rear piece and the body of the car...that could also be a location to bolt them up to the body

[tastyratz]

I would leave a little pumpkin sticking through for the rear vents mainly, maybe some small leuvers that wont terribly impact flow but direct just a slight bit of it over the diff cover.

I would not make any pieces rivet in only, people can manually do that if they really choose but it makes things impossible to change/repair/ or work on if need be.


as far as addressing the exhaust, maybe you could make a raised section in the area a pipe would fit

I.E. instead of

...........................
___(O)___________

make it
.....______.....................
___|..(O)..|____________

This would be something you would have to drop the exhaust to install but it would work more generically.

[PoorMans180SX]

Sounds good, I like your attitude, taking punches and revising your product to the costumer. I'll buy one once all the R&D is done.

[tastyratz]

agreed with Turbo711. If I didnt already purchase the materials to make my own I would definitely be on the potential buyers list if the price was right.

[j00ni3]

Here are pics of a diffuser on an s14

http://192.115.8.73/Images/Nissan/hispee2.jpg

http://192.115.8.73/Images/Nissan/hispee1.jpg

I will buy it and try it.

John


that's really not much of a difference of what he had in the first place...

hahaha... maybe a little wider... but not much difference.. in size or shape...

no? :doh:

[JohnC]

dimension are:

http://192.115.8.73/Images/Nissan/fbea.jpg

http://192.115.8.73/Images/Nissan/3c38.jpg

[tastyratz]

thats actually a beautifully constructed piece, im surprised that one got by me. I dont like the fact that its a composit but Just for curiosity, who makes it and how much do they sell that for?

btw. Another idea for a way to hold this piece would be to make hooks that go between the gas tank and the support strap. Obviously useless on its own but might help hold if used in conjuntion with bolts/brackets

[Kinematics]

Too bad that one is too small for all the PhD in Aerodynamics experts that have all posted in this thread. :blah:

[tastyratz]

you dont need a phd in aerodynamics to have common sense. Logic tells you that turbulance and restriction=drag. period. That will help, however the more turbulant areas we can cover with flat surface, the better the aero will be under the car. period.
Maybe theres not a wind tunnel accessable to tune that panel from 85% efficient to 100% efficient.... but you can easily get to 85 with a head on your shoulders.

[JohnC]

tastyratz,
it is sold in japan for around 22000 JPY.
Do not know who makes it , yet.
I also doubt it is application specific.
I will get a little more info in the upcoming week.
The sell the center piece alone for around 10000 jpy.
I think that if we can get a app specific piece
made up, that would be better even if it was a little
more money.
John

[Sky240PWR]

thats around $200, that sucks! I just spent $510 on the Ab-flug carbon fiber one!

[kouki_s14]

this looks like a fully functional diffuser
http://i3.tinypic.com/wvpro6.jpg
it would be way too much work to get it to fit but it gives you somewhat of an idea of how wide some of these zilvians are expecting this thing to be.
also the best looking diffuser i've ever seen with good ground clearance, kinda..

[Slidin240Wayz]

That is PIMP!

[axiomatik]

hellz yeah. i wish my car kicked enough ass to justify something like that.

[tastyratz]

yea agreed that red car really is pretty damn pimp

[j00ni3]

dimension are:

http://192.115.8.73/Images/Nissan/fbea.jpg

http://192.115.8.73/Images/Nissan/3c38.jpg


OOPS... hehehe didn't see the other 2
heheheheh and i like the sizes of the 3... i might buy it and try it myself haha

going to the track soon too hum..... :2f2f:

[90RS13]

Well, haven't posted in a while...been busy. Looks like I'll be moving soon for a new job. That means my project has to end. I want to thank everyone that posted here though, and I'm glad at least one inexpensive diffuser was found during this thread. My whole goal was just to make a inexpensive diffuser, and now I see that there's one out there so I'm satisfied.

Again thanks everyone,
-matt

[Slidin240Wayz]

your quitting the project??? you should keep going at it. the one posted is only available in Japan, we need something in the USA!!!

[JohnC]

your quitting the project??? you should keep going at it. the one posted is only available in Japan, we need something in the USA!!!


+1 for continuing the project.

[kay_arsen]

look what i found

NISSAN 240SX 2DR 89-94 CARBON FIBER BR Under Diffuser

http://www.aerokits.net/cart/images/nissan/cl757.jpg

http://www.aerokits.net/cart/images/nissan/cl757_2.jpg

http://www.aerokits.net/cart/images/nissan/cl757_3.jpg

[90RS13]

Wow, thanks for the support. I will keep working on this and hopefully finish soon. Then when I move I'll just have to figure out where the work on them will happen. I've got most of what I wanted to do with the mounts and all, I've just been real busy. I have my last final friday, and I've had my hands full with my new baby and all,

http://i3.photobucket.com/albums/y77/MatthewWells/Ella5.jpg
(had to show her off)

I'll try to get a prototype done as soon as I can.

-matt

[spdfreek0o]

kay_arsen where did you find that diffuser on their site? I looked in both 89-94 240sx and 89-94 silvia.

[jdm_s14_zenki]

i say keep going until you get it right. thats what performance manufacturers do except that have much more fundage and manpower and still it takes them A LONG ASS TIME to do R&D till they release the final product. You are on the right track, listen to peoples opinions but not the people that are being dickheads...fuck em.

[S14DB]

I got some horrible fitting rear valences from Chaser. Never heard from them after that.

[jdm_s14_zenki]

I got some horrible fitting rear valences from Chaser. Never heard from them after that.
I'd sell you my JDM ones, but not until i sell my car in about 2 months or so. I will also have my JDM Front for sale as well, when the time comes.

BTW, do those rear diffusers actually do their job on, say, a 240sx thats daily driven and tracked sometimes?

[kay_arsen]

kay_arsen where did you find that diffuser on their site? I looked in both 89-94 240sx and 89-94 silvia.

Ebay seller is aero_parts

no reserve $1.00

cant seem to find the exact link

[S14DB]

Ebay seller is aero_parts

no reserve $1.00

cant seem to find the exact link
$85 shipping....

http://cgi.ebay.com/ebaymotors/NISSAN-240SX-2DR-89-94-CARBON-FIBER-BR-Under-Diffuser_W0QQitemZ8060917525QQcategoryZ33656QQrdZ1 QQcmdZViewItem
http://cgi.ebay.com/ebaymotors/NISSAN-99-up-S15-Silvia-CARBON-FIBER-BR-Under-Diffuser_W0QQitemZ8060917521QQcategoryZ33656QQrdZ1 QQcmdZViewItem
http://cgi.ebay.com/ebaymotors/HONDA-CIVIC-92-95-CARBON-FIBER-B-Road-Under-Diffuser_W0QQitemZ8060917507QQcategoryZ33656QQrdZ1 QQcmdZViewItem
Looks like for the front of the car.
I'd sell you my JDM ones, but not until i sell my car in about 2 months or so. I will also have my JDM Front for sale as well, when the time comes.
PM me when your pinking is up.

[DJPimpFlex]

I cant see how that one would work. Someone buy one and post up some pics!

[Toka Motorsports]

check this out... homemade diffuser on a sr20det powered oldschool nissan
its adjustable, its plywood, and no doubt in my mind that it works

http://www.racecar-engineering.com/content/project_05.htm

http://www.racecar-engineering.com/images/projects/25_11_5/images/Caption%202_JPG.jpg
http://www.racecar-engineering.com/images/projects/25_11_5/images/Caption%203_JPG.jpg

[spdfreek0o]

I think I found my new favorite site. Thanks for the link.

[chmercer]

does he have any weights? looks heavy

[HyperTek]

chaser aero is wack, i doubt they even know what that is.. they just sell whatever they can acquire from distributers. thats not even a diffuser, its a freaking skid pad that someone molded and reproduced in cf...

[axiomatik]

does he have any weights? looks heavy

I was thinking the same thing

[tastyratz]

carbon fiber underneath a lowered car is just plain stupid. its lightweight for the 1 week its on unless the car never sees a single speedbump and isnt lowered at all. maybe for a track car but usually track only cars get something better than just a generic flat underbody panel.

I like the idea of the metal pan your making and if you actually build a prototype around what people are seeking in something like this it will be great, you will be one of the few who has actually tried to pay attention and listen at all.. maybe you can produce a usable product in a fairly open area other people dont seem to want to address.

[j00ni3]

+1 for you to continue this project... and congrats on the baby


very cute haha love babies~

[s14slide]

chaser aero is wack, i doubt they even know what that is.. they just sell whatever they can acquire from distributers. thats not even a diffuser, its a freaking skid pad that someone molded and reproduced in cf...

that thing looks more like a front under diffuser, as opposed to a rear one that this thread is centered around. and yes, there are diffusers for the front to keep the air clean under the front of the car. I have a Yashi Factory "Skid Plate" on my 13, and it's aluminum, thick and strong (withstood track curb bashing without letting the oil pan get dented). I've even seen a few Soarer front kits with a piece pretty much the same molded as one piece with the bumper. Goes all the way back to damn near the tranny. Although I know nothing of this company, I thought unjustified company bashing was supposed to be abolished on this forum.

[MrBojangles]

+1 for you to continue the project from me too...

i've been using a Re-Armemia rear diffuser on my FD at track days, and at first i was skeptical about its actual uses, but on after a couple track days at VIR, I was honestly impressed with the increase in high speed stability.

Why not go off of one of theirs and try and replicate it for the rear of a s13/s14? just a thought. best of luck with the new addition to the family and the project :D

[Ghost Dancer]

http://www.firstmolding.com/fm-aero/RPS13_180SX/rd_270_180_04.jpg

http://www.firstmolding.com/firstmolding/rear-diffuser/rear-diffuser-01.html

[Cashizslick]

Those look almost universal fit. . . . . i bet the thread starter could make that.

[EchoOfSilence]

Just drop it.

If anything, he should make something worthwhile. like this:
http://flyinmiata.com/Store/images/13-69920.jpg
http://flyinmiata.com/images/misc_images/IMG_9008.jpg

I'd buy one of these butterfly braces in a SECOND.

[HKsilvia]

not to be offensive to anyone...but if it really works, when will we have the chance to use it? i personally dun think a diffuser will be practicle for a road car like 240, however i think style is another way of approach. Im sure you wont have the budget to really test it precisely, so my suggestion is to make it more stylish, we are not enough to give u any really professional suggestion. but honestly, A+ for your effort.

[yokotas13]

580 bucks for hte FRP one thats [email protected]

[S14LVIA]

Just drop it.

If anything, he should make something worthwhile. like this:
http://flyinmiata.com/Store/images/13-69920.jpg
http://flyinmiata.com/images/misc_images/IMG_9008.jpg

I'd buy one of these butterfly braces in a SECOND.


That is HOT! i'd buy one for sure

[Impact Black]

Hate to bring a thread back from the dead. However I was curious if there were any other diffusers found for the S13 chassis, specific the 180sx chassis.

Friend of mine told me about the Varis one that I guess you just have to custom fit and trim to fit.

[GSXRJJordan]

Hate to bring a thread back from the dead. However I was curious if there were any other diffusers found for the S13 chassis, specific the 180sx chassis.

Friend of mine told me about the Varis one that I guess you just have to custom fit and trim to fit.

That's how most diffusers are. You're going to want to start with an aftermarket fiberglass bumper anyway, because they're lighter, better looking, and easier to cut up (stock bumpers look like dooo doooo with diffusers IMO) - you're going to have to mod it to fit the subframe/diff area, and exhaust. Other than that, bolt that shit in and pretend like you're making appreciable downforce @ 80mph.

[xs240]

id buy the butterfly brace in a second too

[DeadlyZ33]

That's how most diffusers are. You're going to want to start with an aftermarket fiberglass bumper anyway, because they're lighter, better looking, and easier to cut up (stock bumpers look like dooo doooo with diffusers IMO) - you're going to have to mod it to fit the subframe/diff area, and exhaust. Other than that, bolt that shit in and pretend like you're making appreciable downforce @ 80mph.
A diffuser is not a piece of spacelander nasa technology. It is an EXTREMELY simple concept with its primary design made to vacuum air out from under your car, increasing stability at high speeds. It WILL generate downforce however that usually isnt the goal unless it is a very aggresive design. Rear downforce is usually managed with a GT wing...

I've driven behind a Z with one and watch out for those fall days, the thing leaves a roost of leaves in the air behind you. lol

[MongolPup]

Old thread but a pretty good read. The question of producing this stuff always seems to be that most of the world doesn't have a need for it.

[Impact Black]

That's how most diffusers are. You're going to want to start with an aftermarket fiberglass bumper anyway, because they're lighter, better looking, and easier to cut up (stock bumpers look like dooo doooo with diffusers IMO) - you're going to have to mod it to fit the subframe/diff area, and exhaust. Other than that, bolt that shit in and pretend like you're making appreciable downforce @ 80mph.


Well I'll agree that 80% of the poeple wouldn't have a use for it, but seing as I'm constantly tracking the car, and having issues with air flow at speeds of 150+ then yeah I think I'll need it.