KA24DESOneThree

Anyone have any ideas on how to make some noticeable downforce at speeds less than 90mph? Due to limited funds, time, and the fact that I drive my car to track events, I tend to only drive shorter tracks with low average and peak speeds like Horsethief Mile, The Streets, and the East Loop of Buttonwillow. Also, the purpose of the car is my own enjoyment, and thus there are no rules I have to follow. Aesthetics come second to function as well.

I'm thinking big rear wing mounted up high, canards on the front bumper, a vented hood, and a splitter will lead to noticeable downforce even at lower speeds.

However, since the car will be driven to and from the track I would like to make it so I won't have to replace it every time I need to go into a gas station or drive over a speedbump. I can and will make concessions to surface-street friendliness and accept the fact that if I hit something on the freeway I may destroy whatever hard work I have put into the front bumper because that's life.

Should I ignore an undertray up front, or even an adjustable splitter in lieu of some high-quality garden edging for flexibility? Or should I just do my best to choose entrances with favorable angles of entry? I've seen both Jason Rhoades' front splitter setup and DSG's splitter/undertray and I'm not sure if those would be at all streetable.

How about the rear wing? How high is high enough, and was my choice of a low-priced 62" GT-style wing with an 11.5" deck height a poor one? How high a Gurney flap should I run?

I've been trying to find examples of autocross aerodynamics but since most of the cars are limited by class restrictions it's not much help.

Thanks in advance for the help.

S14SwimShark105

Have you seen the undertray that "Sasha" on ziptied has made? it looks really really nice http://www.ziptied.com/forums/index....2;sa=showPosts you might be able to fab up somthing like that for your s13, he wrote a little review on it on how it performed during one of his races.Other than what you have already mentioned I dont know what else you could do, maybe a rear roof spoiler to help with a little downforce or to smooth out the air that will eventually hit the rear spoiler?

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UNITEDMASTER

Hello, I would say yea do the front splitter/bumper undertray, that will help reduce turbulence & smooth out the airflow ( Im working on one for my car). Then you could make a cover to close the trans tunnle. Then depending on what rear bumper you have you can fab up a rear diffuser to help direct exiting airflow. As far as the height of the wing reasearch says levle with the roof or 1-1.5" lower. Then for wicker bills the bigger it is the more drag it creates so youl will have to find the point where too much wicker effects speed on the longest straight. SASHA is a good example of full undercar aero, but its a full track car, so its a matter of how much of it can you live with on the street,!!!

IMO, HTM & the streets require you to find good mechanical grip(alighnment settings &tire). I have not done BW east loop only,I have driven the full course & west loop. But the east loop is the technical part of the course. So again I would say try to acheive more mechanical grip.

Where are you having trouble turn in ,true cornering phase , or corner exit. Finally A interesting topic in the MOTORSPORTS section.

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S14SwimShark105

I've always thought that for low-speed aerodynamics it's more on how the front and rear diffuser, canards, and the rear wing is positioned as in how many degrees it is angled and the height of the object. You should look into some GT wing manufactures, for example some of them would say the wing is tilted at a certain degree and at 90pmh would produced a certain amount of down force and if adjusted to a more aggressive angle it would produce more down force at lower speeds , and then take that info and try to work it into your aerodynamic pieces and stuff.... haha

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UNITEDMASTER

^^^^ that is correct. Then the trade off is how much created drag is optimal VS the effect on your straight line speed.

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KA24DESOneThree

I have good mechanical grip, I just want MORE. I'm not having trouble in any portion of the corners. I seriously just want more cornering speed and I think that 18x10.5 RPF01s wrapped in 285s would be a bit much for my KA with bolt-ons and I don't feel like buying another set of 17s for street wheels and wrapping my Volks in R-comps.

I suppose I could get my hands on some alumalite and make an undertray. How effective it would be at speeds this low, I'm not sure.

The fastest I've ever been in my S13 is 108mph, and that wasn't even on the track. I'll eventually do full aero, but right now the car is strictly a short-track car until I'm out of college and making enough money to swap in an LS1/2/6. I'll probably see Laguna Seca or PIR sometime before then, I hope.

The problem with adjusting angle of attack without being able to test the wing is that I could just be stalling air off it, which does produce a certain amount of downforce but it also produces drag. Same thing with installing canards at too high an angle of attack.

I've been giving this a lot of thought and I'm still deciding whether or not data acquisition or 255/40s could make me faster than well-thought-out aerodynamics.

I'm on a very tight budget.

UNITEDMASTER

Hello, I would say get tha DATA set up.Alot of our customers have it in their cars and it does not lie. It is such a valuble tool to analize with,becausw sometimes in the heat of the moment you will swear you did this or did that & the car is doing this or that but when you look at the data it tellls a whole different story. I really like the one by MSD or that company they bought GPX2 or something like that. It breaks the track down into small segments,givs entry,exit average corner speed, best speed & slowest speed. It will record Gs as well ,I think most systems will do the same stuff,this one is a bit more easy to useand cheaper compared to motec.

As for more corner speed, by the tires you have I would say you got the grip, maybe a bit too much for stock KA?? Maybe try to free it up a lil just a lil dont want to make the car nervous when its not. Or build a tunnle & full lenght side skirts to seal the bottom of the car. Hey if interested check out this site called Mullsanns corner(spelling) its got tons of info on LMP & Group C sports cars. Im sure you will come away with some good ideas . LMK are you going to HTM in NOV?

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McRussellPants

Aero dynamics are gonna be pretty smash and grab if you're trying to get them to work under 90.


Build a 6in+ splitter as close to the ground as you can man up to.

Get the largest properly designed wing you can. Maybe you can luck out and get a legit aerofoil from a GT Vette or something. That Trash on ebay will prolly work if you stall it out but other than that it probably works about as good as a Duck Bill.



I'd probably just put a Kit on it with ducting and a splitter on the front so it doesn't suck as much air under and be done, It will accomplish 90% of what you're gonna get steezin the stock bumper out with a mega splitter and whatever other pretend racecar parts you can get your mitts on.

S14SwimShark105

Data aquisition is invaluable, I've been wanting to get one of those things for A LONG time but it is so damn expensive but I also know it's worth every penny haha. The 255/40/18 R-compounds would probably be the widest all around I'd go with a stock KA with boltons, I have a KA with boltons at the moment also, and I ran the track with 245/40/17 R-compounds in the rear and it would just not let go. Personally I dont even care about aerodynamics at the moment cause I dont think I'm at that point where I would need it as in I dont time my laps, I dont have to improve by 1/100ths of seconds.

Although I would like a full set of aerodynamic stuff later on, my budget and my skills doesn't allow it or need it haha. But goodluck on everything, hopefully more people have more to say about this.

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KA24DESOneThree

I was/am considering getting my hands on a beat-up Silvia bumper (or using the one I have now) and some plywood and trying my hand at making some hideous, huge splitter. I just don't know where to start and was hoping someone on here (aka Wiisass, Mr. FSAE) could point me in the right direction. I just bought a couple books on aerodynamics but they won't be here for a while.

I've kept my eyes open for some serious wings but there have been none in my price range. I'm hoping that my wing'll be somewhat more effective with a Gurney flap. I did see something about a guy running FTDs in a Vette with a sprint car wing up top...

I'm not a big fan of kits. Not because of the look, but because this car is all about paring pounds, and most of the kits out there are too heavy.

As much as I hate the sound of "pretend racecar parts," and as much as it was probably meant as a slight towards me, it's the truth. My budget right now is whatever the proceeds of me selling random parts can get me. Very few people make race car parts for the 240 at the level I want (which is about fifty times my budget), so I make do.

This isn't for time or whatever. This is to fulfill an addiction to g forces I have. I just haven't been willing to switch to R-compounds yet because they forgive too many mistakes.

I can't afford the G2X data acquisition, but I can afford the G-Tech Pro RR, which I can combine with a camera for a sort of half-assed data acquisition. I doubt I'm going to have over $900 to blow for the next couple years, but I already have a camera and the RR is $300. Guess I'll be looking at reviews of it to see if that might be a decent idea...

I'm trying to make it to HTM but who knows if I actually will. I need to get my car running and set up before then. I need one part and maybe a little electrical work to get her running and setup hopefully won't take long. I haven't driven her in 3 months and I'm getting antsy.

20 til 3

you should check out fresh alloy, search j-rho

S14SwimShark105

^^ Honestly I think thats a horrible front splitter haha but then again I dont know much about aerodynamics, I dont get that plate right under the front bumper, why is it flat like that? It seems like while going straight it would just push the car backwards,shouldn't it at least follow the curvature of the front bumper as well as the splitter also? O well I dont know

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AceInHole

It's flat to collect air above the splitter. More air at extremely low velocity on top, with less air at high velocity below creates downforce.



At speeds below around 70mph it's not worth it to add the weight of a splitter/ undertray. Once you're above 70, the worth is pretty much on the fence, but I suppose it doesn't hurt to try.


As for data acquisition, look into the MaxQ GPS. It's around $300 IIRC, and does a decent amount.

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McRussellPants

Waste of time IMO, Kuah's splitter got jacked up every event without off tracking. god knows what a mangled mess it would have been if it actually hit something.

Buy R comps or good coilovers or something if you crave grip.

IIRC you're on KTS which are undersprung/ super mega underdampened.

Weight will make more of a difference.

2871 SR and you'll run down vettes all day long.

More important things to do than try to rice out the outside of your car to make downforce at speeds its barely seeing on the straightaways. The Diveplanes and Wing and such is gonna have to be so huge for you to feel a difference at 90mph if you are still wanting slippery tires to learn to drive.

steve shadows

What is your definition of undersprung?

KTS is ok, but not great.

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McRussellPants

Jhro dropped the ball.

that shit flexes into the ground over 60mph for sure after adding 1lb of anti lift the the front.

its single sheet aluminum, not even alumicore.

a small splitter on the front will make a difference, not at the speeds you want probably. but it won't look retarded, particularly since you don't have gross ass popup front bumper.

McRussellPants

I'd actually probably say in his case its more under dampened than anything.


If He had a big nifty R-Comps, cage ect. I'd probably go with 12/10. Hankook S15 runs 18/18 so I imagine Im being pretty conservative.



Everything is so hypothetical because every setup will be different.

MomentumGT

Had KTS on our race car with a 10/8 combo and it bottomed out quite a bit. It bottomed out exiting a turn at one time or another a while back. That was the sign we needed to ditch them for something better. They're for sale if anyone wants them.

-Jon

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Wiisass

I don't think it's worth it. You could see much better gains in a better suspension setup, dampers, tires, etc. There is still room for improvement with mechanical grip. And at the speeds your talking about, you're going to see a much bigger improvement with an increase in mechanical grip than you would with any aero work. To get any appreciable amount of downforce, you're going to be close to the point of just generating drag. Which, with an underpowered car, is going to kill you on any straight sections and could end up slowing you down more than it would help.

Do you have any estimate on what lateral accelerations you are running at in some of these corners? Also, it's hard to get more grip if you don't know where you need it? If you aren't pushing the car past the limit of the tires than something is left somewhere. So I think there are other things that you need to sort out first. If you could find out in what situations you need more grip, then you could figure out the best way to get it. I mean I'm not talking about if you're spinning or understeering right off the course, but you should be able to feel where you could use more grip.

But if you want to do aero, just to do it, then go for it. For low speeds though, I would find air management a lot more efficient for everything than any attempts at large amounts of downforce. Good ducting to the engine, brakes, etc and good managing of the air after it passes through it's first target. Or just throw a wing on there, run as high an angle of attack as you feel you can get away with before it starts creating too much drag. Get a decent splitter on there with adjustable arms, so you can also give that a little higher angle of attack at the track, but raise it up a little for driving on the street. But that will probably still get ripped apart. And do the whole underbody. Sasha made a good attempt, but you need to do from front bumper lip to the rear bumper lip and then from side skirt to side skirt, use NACA ducts and the like to vent stuff and see where that gets you.

But I don't know, a good, solid aero package is expensive and not the easiest thing to just throw together. I would really do some testing first. I think it was Racecar Engineering that had a couple how to test aero stuff without a wind tunnel articles a couple months back. If you could dig those up somewhere that might be able to help. I'll see if I can find the issues somewhere around here. But forming a good plan of attack or at least a good test method will be the most beneficial at this point.

Tim

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Wiisass

Jon, how much suspension travel were you seeing? I mean 10/8 isn't too stiff for a race car, but it shouldn't allow for that much suspension travel. Unless there was still one of those giant bumpstops hidden in strut. But I would assume that most coilovers are going to have between 4-6 inches of damper travel without a bumpstop. But if you count the bumpstop, I could see losing at least half of that. I have seen some big, like 3", bumpstops on some setups that are eating up more than half of the available damper travel. Oh, and what sway bars and was it bottoming out in the corners or on big bumps?

As for spring rates, I was planning on trying a 600/500 setup, which puts natural frequencies in a good spot for a lighter s13, sub 2500lb with driver, somewhere around 2.5hz for the spring mass. But it might be allowing too much wheel travel for a MacP strut car at too low of a ride height, meaning allowing travel into a worse part of the camber curve, etc. 18/18 sounds like a little too much. I mean I guess it's really not too bad if they have any real aero on the car. Natural frequencies are right around 3hz depending on car weight and that's normal for cars with real aero.

So it really depends on the setup and on the car. There's a lot that should go into picking spring rates, but this is an aero thread.

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KA24DESOneThree

I read all the way through J-Rho's thread a couple days ago and he didn't say anything particularly conclusive about his front splitter/rear wing setup that I saw. It looks mega-cobbled together, definitely not his normal style. He also left the S-chassis world for a Viper 'vert with chrome wheels, so whatev.

MaxQ GPS is exactly around the price that I'm willing to pay at this point and it definitely does enough.

Kuah's car is also undersprung.

I hate my coilovers because I feel like I can outdrive them.

I'll modify this post later because I have more to say but I need to run to class.

MomentumGT

As far as I can remember the kTS's were installed in the car right out of the box. When added the 10/8 the bumpstop was trimmed, but not by much. As far as weight the car was tipping the scales at 2750 with driver and 1/2 tank of gas. The major problems we had with the KTS was the severe oscillation we experienced when coming out of a turn and or hitting a bump/dip on the track especially, even when the suspension didn't bottom out. The 10/8 spring rate was to bandaid the situation for the mean time which helped but not much, bottoming out was a part of the problem but not the true defining problem. As far as swaybars we're running stock's just for the sheer fact that our car has been seeing some darker days at the moment and the Progress bars just collect dust due to attention to other areas. We are currently on MonoFlex's provided by our sponsor with a 12/9 setup and it's considerably better even without corner blancing.

Sticking with the 'Aero' theme of the thread, in our collective opinion we feel that there is still more mechanical grip to be found in our car before we even start tapping into the aero department. We're thinking of modifying the rear subframe to have the lower control arms sit a little bit flatter so we can get more of a squat action exiting a turn at full throttle versus having the rear end step out into a drift. We got the idea from looking at the XS r32 and a fellow NASA SR-Cup driver. Maybe you have some insight on such a fabrication and or other ideas and I would like to hear it.

-Jon

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g6civcx

Typically, if you want more downforce at lower speeds you would need a larger airfoil and a steeper angle of attack.

Be advised that this setup generates a lot of drag as well.

As said above, you may be better served by spending your time on mechanical before tapping into aero. Aero is hit or miss at best though. So it's your call.

KA24DESOneThree

Ok, so now I've found more time while watching The Professional (and I've taken so long writing this post that I'm now watching Robert Byrd show how damn old he is on CSPAN), and I didn't feel like editing the above post because I'm addressing posts that occurred after.

The whole reason I want to focus on aero right now is because it fits my budget. I can fab the whole thing myself out of a variety of materials for a relatively low price. Anything I want that needs to be machined will be done by my friend for essentially cost of materials or through a barter. Hell, if I wanted a foam core for a wing, he could do it for me and then I'd have to skin it myself.

I just can't afford to upgrade my coilovers, at least not now. Maybe over the summer, when I have a full-time job paying $20/hr, I'll be able to upgrade to something similar to Ace's setup: custom housings with GC coilovers, Koni 86s, etc. I'm trying to band-aid my car's shortcomings without making the car overly simple to drive.

I was thinking about drag, but at speeds this low... does it really create that big a problem? Obviously, I'd have to reduce the angle for faster tracks but for speeds under 80mph I'm not well-versed enough in the field to know if it'd be that big a difference. I know that the amount of air currently flowing under the car is flowing over control arms, tension rods, tie rods, sway bars, the crossmember, the oil pan, the transmission, the rear arms, et cetera... not to mention having 245/40s, can't be helping drag as it is, and a splitter would take most of that drag out of the equation by forcing air around and through the bumper. The rear wing, of course, would be pure drag, especially with a Gurney flap, but then again... straight line speed isn't a huge deal to me and I can always change the AoA to something more sane for daily driving/long-tracking. Oh yes, this car will be my daily while I overhaul my VANOS in my daily. Stupid BMWs. I anticipate getting pulled over a lot.

I've read in a couple books that I can use some Scotch tape and some colored wool string to see where air flow goes. I just need to enlist my brother, a friend, and a camera to capture air flow at certain speeds.

Personally, I agree with McRussell's opinion of 12/10. That'd be ~720/600, and I know that's probably about right with some high-quality, properly damped Konis on big ole R-comps.

AceInHole

I'd wonder if you'd want your F/R spring ratio that close. My autox car has 600/450 (11/8) atm, and I'm even planning on upping the fronts another 50# when the turbo goes back on. As it is, the car is pretty neutral (it can get squirrely when braking too deep). If I were to take it to the track, it'd most likely be something like a 14/10 spring setup, and a bit more in proportion with downforce.

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steve shadows

I dont know how horrible the taiwanese peices (valving) are and as a mostly drag/top speed run oriented enthusiast im just starting to learn the nitty gritty on sus tech.

this is funny because so far on Azenis in the past year doing a couple auto-x and canyon runs I dont have this problem at all with KYB and (all the way stiff on all 4 corners) and 400 lb in front 300 lb in rear.

If i was on Hoosiers? maybe it would be different.

I have seen this happen on cars running Teins or even JIC but we later found out the dampening was set too soft on the adjustment for the dampers.

PS. im at 430-440 whp at 18 psi, so the car just squats once I am exiting apex more than half throttle. I did this by dropping the rear sway completely, removing the front strut brace completely, stiffening the front sway, and putting 25 mm spacers on ONLY the frotn wheels with a smaller contact patch (225 in front, 255 in back) no spacers on hubs in back. I just experimented until I liked the way the car felt on initial turn in and then experimented with traction combinations with exit.

Im sure with an R-comp however the car would be more willing to be stiff on the corner dampening and bracing as well. But this is what has allowed the car to put down at least some of the power before full straight orientation out of the exit of the corner. Otherwise in a low speed 2nd gear turn I will get passed waiting for a place to pin the accleration. its a lot of power in an ass happy car.

It gives the car a slight oversteer on corner exit but its much more controllable than understeer, there is hardly any occilation at all unless i hit a pot hole on the street.

Ill have more data once I get out ot WSIR hopefully within the month-or two.

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fantasya98

honestly, unless you really know what you're doing i would not reccomend changing much. My close friend has a masters in motorsports engineering and he specialized in aerodynamics. I can say that after hearing what he told me, its much more complicated than you'd think and downforce added incorrectly can unbalance the car, create too much drag or even vortices of stagnant air that will slow you down over all.

To me, its much more important to have a balanced car than have one with many things that do not function well together. My suggestion is read books and talk to a professional that really knows their stuff.

KA24DESOneThree

I would talk to a professional but frankly most professionals don't give a rip about aerodynamic effects below 100mph. I can't blame them... half a second at 125mph is much more effective than half a second at 65mph.

Most would also say to upgrade mechanical grip before messing with aero, which is the correct thing to do but my limited budget says no. Besides, I do not want to bother busy people with minutae, at least not until I've read both books I ordered from cover to cover.

Steve, you'll find that despite all your horsepower, if you get a few more mph out of the corners your lap times will decrease dramatically. In a car with that much power and such small tires, you should have it tuned for understeer because your right foot can control the oversteer.

Ace, I don't really know what kind of spring rates would be best for my application. I'm kinda spouting random numbers for the spring rates because I think the 240 needs rates that high or higher in the front when cornering on big, wide R-comps. In the rear, it's more a function of balance and traction. I anticipate running 305s all around eventually and with that much grip, who knows.

MomentumGT

Definitely with r compounds more stress is put on the suspenesion. From your description it seems like you softened up the suspension to dial out the oversteer induced by having such high HP #'s, but then again having the throttle pinned with that much power on exit will make anything step out. What we're trying to do is to get the car to squat and also not sacrificing roll stiffness in softening up the springs, sways, etc...What we're conteplating of doing is swapping out the stock subframe with a s15 sub and or fabricating tabs on the stock s13 subframe for the front part of the control arms to sit lower thus dialing out the anti squat. This will help weight transfer to the rear wheels upon exit a lot thus putting more tire into the pavement and giving the driver more ability to give more throttle on exit, assuming camber, etc, etc, is already tuned in. In the end increasing mechanical grip for a not so grip happy s13. A great example would be of the XS r32, which has very similar suspension geometry as the s13. In some corners at BW the r32 looks like its getting up on 3 wheels on acceleration as the weight transfer on corner exit is huge making the car set and squat. If you ever get a chance to see the car up close check the subframe as this is what we're trying to bite...I mean create for our car. When you're able to get your car onto the track and experiment I'd like to hear what kind of answers for more grip you come up with so to possibly maybe mesh theories together.

-Jon

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AceInHole

305's up front is pretty big, and to clear the strut you'll need a low offset, which gives you a larger scrub radius. I'd stick with the 285's up front, since they're easier to find and have the lowest overall diameter of the larger tires.

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