bowflex

i'm making around 350whp on my S13 with an SR-20 engine swap. My car gets to 150mph no problem but then i start loosing control because i don't have enough down force. i don't really want to get a wing because that would ruin my look, and it's expensive. i've thought about getting a splitter, but i only have 3in of ground clearance in the front and don't want to get a splitter only to ruin it. any advice? i'm going to get a boost controller and increase my boost to 12lbs so i should be getting well over 400whp and want to make use of it, but it's super shady taking my car over 150mph the way it is.

cc4usmc

Dude, just put wings on it. Why stay down when you can go up?

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Rayne

How do you know you do not have enough down force? Do you feel the vehicle lifting?
Why are you doing a 150mph?

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Koopa Troopa

400 at .8 bar? WTF turbo you using?

I feel I should lecture you on aerodynamics and how cars without the proper aerodynamics can behave at those speeds but I think it would be alot more interesting if I let you figure that out on your own.

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sidewaysil80

lol, wtf setup do you have to where you are getting 350hp at LESS then 12psi?

damn beat me to it koop troopa

Koopa Troopa

Oh and anything I have to tell you, you won't do because it'll ruin the look of your car so why bother making this thread?

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chibo

That's weird, unless my math is wrong you're going to need at least 440whp just to overcome the air resistance to reach 150mph.
(The S13 has a frontal area of 19.6ft^2)

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Geno750

Downhill ftw?

g6civcx

I have a question. What makes you think the lack of downforce is causing you to lose control?

Perhaps going 150mph would cause any car to start losing control?

g6civcx

You don't calculate terminal velocity with power; you calculate it with thrust.

Rear wheel thrust is calculated based on torque.

Go back to your engineering physics books

chibo

Fawk, my failboat just sank.

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MudRacer

Install rocket jets facing upwards and turn them on after reaching 150mph to keep your car from lifting off the road. It may, may not work. Also your tires might blow up.

'Smash Lab' tried something similar, but retarded. Slowing down a big rig by installing jets that go the opposite direction.

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g6civcx

It's okay. Good try though

coreansurfer

meh, you made an intelligent attempt, which is way more than what can be said for most people on this forum. +fake rep.

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aznpoopy

try this. the grassroots motorsports $2007 challenge car had a fan off an abrams tank mounted under and inside the car so when it was switched on it generated a massive amount of downforce via suction

http://blog.cardomain.com/blog/2007/...halleng-1.html

http://www.vetteweb.com/features/vem..._assembly.html

have fun.

nissan_powa

I say go w/ the Huge GT WING. LOL

coreansurfer

question:

roughly how much whp/torque would you need to break 150mph?

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xkamikazestormx

thats more thane enough clearance

g6civcx

I don't know the number exactly but I can tell you what variables are needed.


Drag (physics) derivations - Wikipedia, the free encyclopedia

To obtain a certain speed, your engine has to overcome drag forces at that speed.

You also have to overcome rolling resistance of the wheels, but that is pretty much constant and is relatively small compared to drag forces.
Rolling resistance - Wikipedia, the free encyclopedia

bshotts

I wouldn’t call it terminal velocity (like a free fall) so much as simply top speed and that happens when the aerodynamic drag force is equal to or greater than your propulsive (thrust) force like g6 said earlier:

Fdrag = Fthrust

Drag force - Fdrag = .5*ρair*V2*A*Cd and Thrust force – Fthrust = P/V

Where ρair (density of air @ sea level) = 1.23 kg/m3
V (car velocity or speed) = 150 miles/hour for your case
A (frontal car area) = 19.6 ft2 (S13 240SX and similar for S14 I assume)
Cd (drag coefficient) = .30 (S13 240SX), .33 (95/96), .34 (97/98)
P (engine power) = unknown

Simplify and isolate P:

P = .5*ρair*V3*A*Cd

Plug and chug:

P = .5*(1.23 kg/m3 *((150 miles/hour)*(.444 m/s) /mile/hour)) 3 *.54 m2)

Now P = 98000 kg* m2/s3 or 98000 Watts where 746 Watts = 1 bhp
So P = 131 bhp

Or in other words taking a roughly 17% drivetrain efficiency loss…….. 110 whp!

So, what this means for you OP is that you must make approximately 110 whp to reach a speed of 150 mph in that bad S13 of yours and that is neglecting rolling resistance (from wider tires or a real janky alignment) and no additional wind forces opposing your motion.

Doesn't seem like alot but it's exponential trust me.
175 mph = 175 whp
200 mph = 265 whp
250 mph = 500 whp
300 mph = 875 whp

cc4usmc

Wow that just gave me a headache.

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bshotts

Come on man....that physics and math crap CAN be useful! At least that's what I convinced myself everytime I thought about jumping off the parking garage ahhaha

coreansurfer

fuck i wish we had rep back, this is def a rep worth post

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ranger240

youre going 150 mph and are complaining about the high cost of a wing? and a ruined look? cheaping out @ that speed is a great way to die

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Silverbullet

good ol fluid mechanics.

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Matman03

When you put a big wing on a car it is going to change its aerodynamics, the less resistance the faster you can go. Why do you think that the bugatti veyron tucks its spoiler down when it goes faster....Either way, its not too smart to go that fast if you are not in control. Plus there is no way you have that much HP at that low of boost. I think you are full of crap. Just me though.

jskateborders

Well Ive been 145ish at 6 grand in 5th when my sr was stock (obviously fuel cut defender)... so 150 isn't that far off. Im pretty positive I would have been able to make if there wasn't some sort of limiter at 6 grand. Im assuming its a rev limiter tied in with a gear sensor, seeing as the ecu was not seeing speed. Now Ive got a shit ton more power, so Im sure 170 is attainable, but whats the point? I guess if your a speed junky, cool, but tickets and probable death arent worth it for me.

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BillyTheKid

I know this thread is kinda old but I would like to add a few words to it, mainly because it popped on google when I looked for the drag coefficient of s13's and while I was going thru it, I saw a little mistake.

First, i believe the 131hp you mentionned are the effective hp ( whp ) and not the bhp as you said. Think about it, would a 50% drivetrain loss mean only 65 whp is required instead of 110 ??

the results would then be as following:

150 mph => 130 whp = 155 bhp
175 mph => 210 whp = 245 bhp
200 mph => 315 whp = 365 bhp
225 mph => 450 whp = 525 bhp
250 mph => 615 whp = 720 bhp
275 mph => 820 whp = 960 bhp
300 mph => 1065 whp = 1245 bhp

and for those who wonder how fast the books says your car is going, you can play with the variables and get:

MaxSpeed = ( WHP * 746 * 2 / ( AirDensity * FrontalArea/10,7 *CoeffDrag ))^(1/3) /0,444

just copy the formula ( from the equal sign ) in excel and replace the variables with these values...

AirDensity = 1,23 ( at 15 degrees Celcius )
FrontalArea = 19,6
CoeffDrag = 0,30 ( FastBack ) or 0,32 ( Coupe )

it become, for me...

MaxSpeed = ( 280 * 746 * 2 / ( 1,23 * 19,6/10,7 *0,32 ))^(1/3) /0,444
MaxSpeed = 187,77 MPH

but this is ONLY if you make max HP at the corresponding RPM... but it's a rough approximate, in my case, considering the engine turns at 7500RPM at 180mph ( in fifth gear with stock tire diameter )

hOngsterr

this guy crashed at 148 mph.

&fs=1" width="644" height="390">http://www.youtube.com/watch?v=<object width="640" height="385"><param name="movie" value="http://www.youtube.com/v/aFxH7Lqvp00&hl=en_US&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/aFxH7Lqvp00&hl=en_US&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="640" height="385"></embed></object>


sooo if you dont have a wing nor a rear diffuser then i dont know what else can keep your car down. if your so much about looks then dont go fast lol.

or be baller and waste your time on installing one trunk with the wing and one w/o so when your DD you can rock the wingless one and track you replace it.

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