Aerodynamics

[Edub1]

Any of you guys who have pushed the speedo up high have probably noticed that our cars turn into hovercrafts at a certain point.

I'm wondering what areodynamic improvements could be made to combat this. Obviously a wing on the back will take care of the back but for the front...

I was considering a "U" shaped piece similar to a skid plate underneath the front end in hopes to create a venturi effect under the car and suck it down against the road. Maybe even one in back too because I don't want a wing on my coup.

Venting the hood might also help because the hood is kind of shaped like an airplane wing which creates a low pressure on top.

Anyway, think it might work? If not, what is your idea?

[Chezedik]

Yes, at about 135mph, the car starts shaking like mad, a little scary. But in all honesty, I probably don't need to be going that fast. Are you trying to create an Enzo style front spoiler? I you can, and make it work the same way, I think it would be neat.

[Edub1]

Never seen one and I want something hidden. I think the under car venturi has potential though.

[Chezedik]

No, I totally agree. If it weren't for you going turbo, I think you could even modify the air dam. I think that a properly designed skid plate, like on the R34, would do a lot too. But I can't decide if louvreing it would make your problem better or worse.

[thekawaii]

does good suspension setup (like lowered stiff coilover) help that problem?

[Chezedik]

Not a lot, in fact, lowering a car can make it worse.

[thekawaii]

then how would you creat low pressure under a car. i was thinking doing that too but i don't have tool to cut,weld, measure properly, etc tools...

all i have is that 10mm socket for my S13

[Chezedik]

As mentioned, the R34 uses a full body skid plate that prevents air from getting trapped in pockets. But it is worth mentioning that it is made of carbon fiber and doing so, even with aluminum, would be heavier than one would care for. Also, as mentioned, using a specialized wing to replicate the venturi effect under the car could do so. But in this instance, the venturi effect is fancy talk for an undercar wing in a tube shape. The more important goal would be to keep the air from entering under the car. One could fashion a special wing, but most drift kits are designed well enough to keep a lot of air out. Also, you could go with what many call the 'Home Depot' body kit. That is a roll of yard separator, screwed in to the front air dam, nearly to the point where it would touch the ground. It is a few bucks and would help a little. The problem with it is that it would also create drag, be too malleable to expect much from, and it looks a little tacky. So, the best idea often comes down to getting a WELL-DESIGNED body kit. Generally, the ones that actually are aerodynamically designed look gaudy and are expensive. As I have said before, maybe we just do not need to go that fast.

[PapaSmurf2k3]

I would think porting the hood would help, as far up as possible. Seems like air would be entering low, exiting high, increasing the overall "wedge" effect of the car.

[Chezedik]

I agree with that also, and provide additional cooling of the air charge. But speaking from experience on my first S13, water in there can spell disaster, not to mention a difficult diagnosis

[Edub1]

I'll be getting a body kit but I'm not counting on it being to aerodynamic.

Also, keeping air from under the car might not be enough. If you look at the hood, its curved shape kind of resembles the shape of an airplane wing and I suspect it acts like one. If I'm right, venting it would be a partial solution but I certainly don't want water in my stuff. However, a drip pan under the vent might solve that problem and still allow the air to be drawn through. Ever see that one guy's write up on his home made vent. Looked damn good I think and looked to be positioned over the fan shroud.

I was wondering how it would look just to cut a cool looking pattern and put mesh in from underneath. You could even form the mash to be flush or even protrude. If you really wanted to get fancy you could get some foam so that they would look like a super rad air cleaner system. These would have to be huge to reduce the vacuum created by the hood but it sure would look sexy anyway.

I think I'm going to make an upside down wing and see if I can fit it up under the car like a skid plate. If air is going to get up under there might as well use it to my advantage.

BTW, for those of you who are wondering. By forcing a volume of air to pass through a smaller area you increase its speed and cause an area of low pressure that can be used in a number of ways. This is what we mean by venturi effect. Contrary to intuition, an airplane wing does not cause air to push up from underneath. Air flowing over the upper curved surface has to speed up and causes an area of low pressure on top that sucks the wing upward from the top. That's why we are discussing a well designed skid plate as an upside down wing, so to speak.

[Chezedik]

BTW, for those of you who are wondering. By forcing a volume of air to pass through a smaller area you increase its speed and cause an area of low pressure that can be used in a number of ways. This is what we mean by venturi effect. Contrary to intuition, an airplane wing does not cause air to push up from underneath. Air flowing over the upper curved surface has to speed up and causes an area of low pressure on top that sucks the wing upward from the top. That's why we are discussing a well designed skid plate as an upside down wing, so to speak.

Well put. I think the hood idea is a good one, but you would need to be careful, because it could easily become rice quickly. You may think of getting the hood louvred by a hot rod shop. It may not look too bad, it would have vents like Z3 fenders.

[Edub1]

Rice? I'd be more worried about ***** the thing up all together the way I do things.

JC Whitney sells louvered pieces but are you telling me they can cut them straight into the hood? How much does something like that cost? I think that would look sweet.

I doubt it would cure the lift (assuming there is any) but for cooling...

[Chezedik]

Yeah, it isn't too bad, and being in Detroit I have to assume you shouldn't have too much trouble finding a hot rod shop in your area. And if you want to know if it causes lift, just take it off. Having driven without it, I promise you that it does.

[Edub1]

Well there you have it.

I just might do that with my hood. I just can't tell them it's from a "jap" car or they will throw their tools at me.

[Chezedik]

Nope, not if your money is green.

[HolyShiznit]

Ok, my 240 with the new tune was low 400 wheel horsepower with out nitrous. I could easily get up to 142 which is where I would have to shift into 5th gear. Why would you want to modify your car so that it would feel more comfortable past that? Why would you need/want to push your car in 5th gear? It's an overdrive gear....not the best thing to be doing to your car. Obviously no one on this board *yet* has needed to worry about aerodynamics like that in the 1/4 mile.

Seems to me like it's a waste of your money to alter the car for something that is entirely useless. The car simply runs out of gearing past that point anyways.

[jollygreen]

with the various engine swaps for the 240 and people who think about racing outside of the 1/4 mile, for instance roll-ons, speeds in excess of 150mph are quite concievable. personally i'd like my 240 to be able to reach 200mph.

[Chezedik]

For 200 MPH it better be built like a Le Mans car.

[Ichi-Go]

For 200 MPH it better be built like a Le Mans car.

Correction... It better be a Le Mans car.

[TravBear2]

Good Luck with this... Keep us updated on what you find out... I like you like to do high speed runs... 1/4 miles get old fast... You never know where a COP is when you are going down the freeway... Thats a little more fun... Or autocross for the legal stuff of course.

[nismofly]

actually one of the ideas ive had for my hatch, since i dont want to run this one wheel to wheel, would be the silver state classic...this would be a great venue to work on high speed aero for the s chassis

[jollygreen]

which model do you guys think would be the most aerodynamic? the s13 or s14? i've seen vid of a s14 doin 200mph. also i was thinking about making a undertray out of fiberglass or some kind of plastic sheeting, any thoughts?

[HolyShiznit]

with the various engine swaps for the 240 and people who think about racing outside of the 1/4 mile, for instance roll-ons, speeds in excess of 150mph are quite concievable. personally i'd like my 240 to be able to reach 200mph.

Ok once again you have failed to tell me how you are going to gear it. All the available trannies are 5 speed. Which means you still have an overdrive gear to deal with. To reach 200mph in an S chassis would require an INCREDIBLE amount of wheel/tire/suspension/power/transmission upgrades. And I have raced in roll ons, and going past 150 mph is insane. If you can't pull a car by 130 then in an S chassis you aren't going to beat it. I have a 2000 Corvette with a 150 wet shot. I am telling you going past 4th gear in an S chassis is stupid. I haven't even gone that high in the Vette.

The only slightly conceivable way I can see this happening is a 6 speed transmission swap with a **** load of power and some insane aero work.

[Edub1]

It isn't the point of this thread to debate why we want our cars more stable at high speeds. I'm after an all around sports car, not a strip car. Our "sports cars" could use these improvements at a good 85MPH freeway clip which is normal freeway speed in Detroit. A sports car ought to have some respectable top end.

Remember, most people think it's pointless to modify a car at all.

So, for those of us who want a little more top end, lets please get back to aerodynamics.________________________________________________

I liked the idea of the fibergalss underbelly but why not aluminium? The idea is to make a shape that forces the passing air into a smaller space. You're not going to want funky shapes.

[nismofly]

i hate drag racing with a passion, there i said it, therefore im not worried about acceleration nearly as much, and i can afford to gear it for top end a little more...if im competing silver state classic, i would probably start lower in class of course but eventually move up to 125mph class and probably 150 with enough power, sustaining and turning at speeds like that, you can feel a little squirreliness

also, the stock s13 hits 5k in 5th at around 132, i havent personally done so but ive heard from several people that with a *stock* ka you can hit and sustain that range of speed at faster tracks like watkins glen, where it would help even more to have your platform as stable as possible

[Edub1]

140MPH and stable is respectable for a sports car. I'll be interested to see what my body kit does.