Ok, so this past weekend, the gears were turning in my head, and I got to thinking about the aerodynamics aspect of our cars. I want to do some open road racing in the future, and I was thinking of ways to clean up my car and keep the front end planted at high (150+) speeds.

The one and only time I did a top speed run in my car (reached a calculated 155 mph) the front end was very twitchy and loose.

So far, I've come up with lower front and side skirts, belly pans, and air extractors on the hood similar to the Japanese hood to allow cooling air to excape from under the car, permanent headlight covers made of plexiglass, and a seal along the front edge of the hood.

I've been looking for books that I can read up on that concern the design of things like this, but haven't had much luck so far. Does anyone have any experience with stuff like this?

 

agreed i know a couple times i have maxed my car out the front end doesnt feel dafe at all like its floating on air at those speeds.. i agree there needs to be a fix to keep the front end more planted to the ground at those speeds.

 

consult the ricers, but put one on the front too

http://www.jcwhitney.com/autoparts/P...-10102/s-10101

* Fully adjustable to create just the right downforce for better traction, easier handling and more stability

but seriously, what kinda strut are you using? if you get ones that have less bound or rebound, i dont remember which it is, whatever that makes them extend slower/harder would help

 

***







j/k I'm not even concerned with suspension at this point, just thinking about the aerodynamics. You can believe if I'm going to put the work into the aero design, the suspension will be up to par.

 

you could go as far as doing the whole bit, front splitter, belly-pan, rear diffuser, etc. but rember you have to keep the tranny and rear-end cool too. for most of those parts to really be effective, you have to have the car LOW to the ground, and the diffuser/splitter need to be well designed, if they are going to create any real ammount of downforce.

 

Which is my whole reason for creating this post, as I'm trying to learn just how to do this. Is pretty much the only good way trial and error? I mean I've got some ideas, but I don't exactly have a 5 mile closed course anywhere near me

 

well, the key to both is obviosly the creation of a high pressure zone above the 'ledge' on the splitter, and a low pressure zone in the back of the car, under the diffuser.

I don't claim to know how to design one, but I do understand it all works.

you might try to dig up a copy of a few books on race car areodynamics, i am sure they will touch on what makes a good design.

These might be some good ones to start with......
-----------------------------
Aerodynamics for Racing and Performance Cars -- Forbes Aird
How to Make Your Car Handle -- Fred Puhn
Race Car Vehicle Dynamics (R146) -- William & Douglas Milliken
Fundamentals of Vehicle Dynamics (R114) -- Thomas D. Gillespie

 

there was a 200mph 3rd gen in car craft awhile back, like a year or 2.....try looking that up

 

it was a bird, and didn't it weigh like 5000 pounds?

 

Thanks for the titles, I'll see what I can dig up with those. I found some good photos on some of the open road racing sites, but I'd rather know what I was doing and why instead of just slapping something onto the car and hoping it helped.

 

yeah I just talked to my brother and he said he's got it at home, but I'll have to wait till Thanksgiving break to get it. hopefully that will have some useful information. right now I'm just kind of basing my ideas off of photos of cars at competitions.

 

ya im pretty sure they went into detail as to how the car was setup for high speeds

 

sweet deal, I'll definitely check that out then. thanks for the info

 

I am actually building low pressure areodynamics into a vintage Mini cooper I bought. The beauty of this car is FWD. The rear section underneath is wide open so I canraise the floor cavity under and behind my seated position and get the nose as low to the ground with an airdam (short wheelbase, and short nose extention in front of the wheels make the car drivable on surface streets still with very low dam and skirts.)

The other thing I am building into the design is a rear radiator. I plan to put a very large (compared to the stock mini rad) Scirroco dual core alum rad just above the bellypan in the rear and will be vented out through to the rear boot lid and run full time off of dual fans. This setup will help assist the vacuum pull underneath the car to further create a low pressure zone underneath the car and draw it down at high speed. It gonna be the snitchz

 

There's a big difference between stability and downforce at speed. Stability is gained through not letting air lift the car off the pavement. Downforce is the addition of air-induced weight without the mass to produce the effect. Lazy top-speed racers cheat by adding a lot of weight into a car - which can overload tires to failure very easily.

All you really need to do is vent all underhood air (from the radiator) over the top of the car and minimize the amount of air getting under the car - using a lower front spoiler. Diffusers are not really necessary as they will increase downforce and therefore drag. Rear spoilers are also not really necessary as the body shape of a thirdgen is suited to keeping the *** planted with a factory rear spoiler.

The books that TexasLT1 mentioned are good - I have most of them.

 

paul,

the idea of the diffuser and a good areo package, is to keep the drag minimual while creating downforce. obviously the goal is not to lift, but the increased traction from the downforce is a plus.

 

if you run the stock rear SPOILER and not the "aero" wing, and the car is slightly lowered.... its aerodynamicly great already. it wont try to lift anything except the hood.. (because of the headlights.)

you just need a good suspension. for control... ive driven 3rdgens and 4thgens over 160 before.... with good suspension, the 3rdgen is great. not scary at all..... but with worn parts, it can be a nightmare at just 90.. lol

when i first got my 82, it was scary going 85 in it.

the 91 vert has only been topped out to 121 (according to GPS datalog) and it felt fine. actually, it felt great.


paul_huryk:
air induced downforce also loads the tires and can cause overload. so how they gain the extra weight is irrlevent. they need better tires to begin with.

 

i've been upwards of 170mph in my car, and i can tell you that it used to really really scary.....now with the koni adjustable shocks, all new front end parts, and better springs.....it rides nice and smooth all the way up

 

FAST

 

Nice PHOTOSHOP work :rockon: .

 

I can tell you right now just looking at that picture above that the hood is producing more lift than downforce. Notice how the back of the hood where the windshield meets is relatively low. Well at high speeds a low pressure zone is created and it doesn't help that we have relatively wide hoods . Hence the lifting. Rake the car slightly and do everything that NASCAR does and you'll have a stable high speed car . Seriously though, look at how they push down the nose as much as possible. Our option is to go with a cowl hood with considerable slope and/or offset the difference with some downforce. The downofroce could come from venting the radiator air above the engine and through a cowl hood, ducting, belly pans, and spoilers. You know, the spoilers that spoil the air flow (friend told me that joke).

 

Exactly, I've been to 155 in mine and I'm not about to do it again until I: upgrade the brakes, rebuild the front suspension, do something to take the air off the front.


Paul, thanks for the info. I was thinking if I switched to a small cowl hood (like 1 1/2", maybe 2"), as well as take the rear hood seal out, then drop the nose a little more and add a skirt, and add some smoothed headlight covers, that would probably take care of the front lifting problem. That is my main concern first is keep the front planted. Once I can figure that out, I would think you would definitely want some, even if its just a little, downforce to help keep the car planted when you're taking turns at 150+.

 

On another note, anyone have any urethane experience? I got to thinking about making a lower front "spoiler" out of urethane like ME Leigh's photoshop or something relatively soft like it to have some give. I thought about fiberglass at first, but that would just crack and break I would think on a rough road.

 

It has nothing to do with better tires - it has to do with the load rating the tires have. To be really safe in high speed driving (over 175mph), you need to have close to 2x the load capabilities as the car's weight (i.e. a 3500lb car would need 7000lbs of safe tire load limit). That is why you will see a lot of high powered heavy cars (like AMG Mercedes) limited to a certain speed - they would overload the tires well before top speed occured - which could result in a fatal crash.

The two things you need to do in order to make a car stable at speed is limit the amount of air going under a car (though spoilers and hood venting) and keeping the air that has no choice but to go underneath free of obstruction (and thirdgens have plenty of them).

What would be ideal would be to have a front vented hood (like the old Ford GT40 race cars) and a front spoiler that comes down low (and doesn't increase scraping on the ground) - something like the new Audi A4 nose (but lower). Side skirts would keep air from getting back under the car by the doors. The tough part would be making belly pans that actually worked with the tricky exhaust and rearend placement.

 

I'm working on a drawing of something like what you're talking about. Once I get it finished and scanned in I'll post it up and see what y'all think.

 

Guys... I think you all have different ideas and concepts regarding the "aero" treatment of our cars.

I would recommend (because there's not enough space here to properly deal with it all) that you read a book on aerodynamics, for example "race car aerodynamics", you can get it at www.motorbooks.com . That will show you, not just how a single piece works, but gives you an idea on the whole package.

Check out some cars that run for example at the Silver State Classic, or Bonneville (Several F-bodies have made record runs there); Andy Granatelli even ran back in '85 or so a third gen with turbos that went upwards of 200mph at El Mirage.

A lower front like the one on the photoshop (with a flexible dam nearly touching the ground, like the Cheverra Camaro that ran at Daytona back in '81 or so), light covers the air is not trapped in the pockets, a lowered ride height and stiffer suspension, appropiately ducted panels behind the grille, a means of evacuating the underhood air, side skirts to prevent air from getting under the car from the sides, and ALSO, something like a bigger rear spoiler out in the back to balance the car. If you create too much front downforce, the car will oversteer and be very dangerous. Hope you are mounting a complete rollcage and safety harnesses too, and a remote fire extinguisher.

And for somebody who said something about tire loads and speed limited cars... not so. The tires have "speed ratings" (you all know about that) and those speed ratings are taken at 10 minutes constant speed. I would use nothing less than ZR rated tires for running at those speeds. Germay has imposed speed limits on most of their cars even though you can run as fast as you dare on their Autobahns. Same with motorcycles, which are "supposedly" limited to 100hp.

Play it safe.

 

FASTER

 

 

You guys are getting rediculous with a street car. If this car sees any street time at all your wasting your time.

 

This is what the nose of a 200mph car should look like. Don't try this with your Camaro boys and girls, you're fooling with mother nature.

Thunderboy, your high if you think vehicle load wreight doesn't play a part in tire delamination. It not only plays a part- its one of two determining factors (heat being the other). Put a Y rated (186+mph rating) tire on a 5000lb car at 140mph across a hot asphalt road for 30 minutes and I'll be reading your obituary.

 

I'd like to further explain some things about the car I pictured above. This car is wind tunnel tested to the speed it runs (this car ran Le Mans) and the apropriate spring rate is detremined to the average and top speeds it will be running at the particular event. (Charts saved form testing & racing back in the late 60's are now the determining factor of this Vintage car)

The front end in the picture looks like a 4x4 sitting still. The cars overall weight is about 2300 lbs. With the right spring rate- at 140 mph the car will squat down 2". Also with the proper spring rate, at 230mph the car will squat down 2". The spring rate is determined by the speed it is intended to run. At 230 mph, this car produces about 4500 lbs downforce and runs a harder compound tire than it would on a track that has a max speed of 140 mph.

Have I sat in it? Yes

Have I driven it? Only in my dreams.

 

Hears a shot of some of the fastest production "street" raececars in the world currently. This is a recent TCRA event at Calif Speedway. Wings aren't just for imports anymore. The second from the end is one of the entended body production Vipers suited for LeMans.

 

Who said this was going to be a street car?


Initially, yes that was the intention, but as the discussion progressed, some of the ideas brought up I would only do on a purpose built car.

 

I was just thinking of what would be a good idea - how about a 2 piece front spoiler that can be either stock clearance or ultra-low clearance (like the photoshop pic). So that way you can run it on the street and still add the spoiler on for top speed/track duty.

 

Thats exactly what I was thinking about, I was just trying to come up with a way to mount the high speed spoiler on securely. The side skirts would be no problem, and if one still wanted to do belly pans, they could easily be secured with Clecos. hmm....


The other idea I had, was just make an entirely new front spoiler that would be put on for the races, then taken off for street driving. It would take a little more work, but its not that hard to take off the front spoiler anyway, and this way you could keep the car looking totally stock.

And finally, to go along with my idea that I'm still drawing up, how much radiator surface do you think you would need at 160+ mph to keep the engine relatively cool (190-210)? I think with that much air coming through the front, you wouldn't need the full size that our cars need for street use. *Edit* Keep in mind, I'm thinking with adequate ducting, not the stock setup

 

THEN
I think you just answered your own stupid question- And you roll your eyes at me?

 

Yes, two totally different ideas for two totally different cars.


I think it is pretty obvious some of this stuff would be totally rediculous for a street car, but no one ever said thats what we were discussing. Its called throwing out ideas.

 

Hmm.... street car aerodynamics for everybody; no downforce, no lift.
That being said and the problems with f-body's getting nose heavy at high speed it would appear there needs to be a way of decreasing the lift with either corrections or downforce. Added downforce is ugly, just fix the reasons why it lifts. Bellypan the front level to the ground and do something with the hood to remove engine bay heat. Wrapping headers is a good way to keep the heat out of the engine bay. Removing the weather stripping also works very well. If I were to do what I just suggested and I had a stock hood (I have cowl) then I'd also jack up the rear of the hood a tad. That's where I would start so take it or leave it.
Downforce; lower the front as much as possible keeping the rear as high as possible (roll centers need to be considered). Installing a spoiler in the front could help along with a very low front valence. Only troubles with that is getting air to through the radiator!

 

Now you own two different cars? Lets see photos?
Look partner, You came in here asking if anyone has any experience with stuff like this- Many are giving suggestions but have never done it- I happen to have very much experience with racecars and driving (and to throw sh*t into the wind, I've been calculated at 186 in a car and 152 on a bike), And am also currently working on a project car right now doing this very subject. If you don't want imput from someone experienced in this area, the next time don't ask. You have alot to learn still hotshot, and need to learn to treat those in the know with respect- Dry your ears.

The thing everyone here is neglecting to realise (and I stated above already) is you can't just add an airdam and go 150mph. You need to taylor the spring rate and suspension settings to compensate for the higher forces of bump impact.

What is happiening to you at the so called 150mph is the nose end is too soft and compressing then on rebound lift raising the car unstable. Work with the suspension alone will cure this problem. Areodynamics will make the car cut through the air to attain a higher speed at a quicker rate, and is not entirely designed to just make the car stable. The speeds you are dealing with are not that critical yet for the car "taking off". This begins at about 170mph headwind.

PS- I have a brick ('89 1/2ton truck) that runs completely stable @ 138mph due to an adequate suspension and abosolutely no aerodynamics- completely stable.

 

Maybe I need to "dry my ears" but you need to clean your glasses. When did I ever say, "I am going to do this to my own personal street car and drive it everyday on the road like I'm at the Silver State Classic"? Did I say, "I want input from everyone except vsixtoy"? No. I came here looking for info solely on the aerodynamics of our cars. I know full well it takes more than just aero work to get our cars to go this fast safely. In this post, thats all I'm worried about though is the aerodynamics.

Initially, my intention was to get ideas for minor modifications I could do to my own car to run in some of the open road races next year. But as the post progressed and more radical ideas were thrown out, I thought it became obvious we were talking about stuff someone would only do to a purpose built car, like you mention you are building, and like I would like to build in the future. That is why I kept going about race car modifications and not street-friendly things. In fact, as my senior engineering project, I plan to do extensive aerodynamics testing using my car and one of the runways here at the Academy. My plan right now is to use load cells mounted in the front and rear suspension to get baseline lift/downforce readings, then make incremental aerodynamic modifications and take further readings.

Now, I meant no disrespect after you said we were getting rediculous for a street car, I thought it was clear we weren't necessarily talking about a street car. Obviously I was mistaken and shouldn't have assumed. I apologize for getting testy, and would indeed like to hear from as many people as possible, such as yourself, who have experience in this area.

 

ok, here is the drawing I spoke of in an earlier post. the main thing I wanted to draw up was the radiator idea. seem feasible? water from the engine would go to the rear radiator first, then to the front one so as not to heat the air as much between the two.

and yes vsixtoy, this is for a race only car




I forgot to label the pre-'91 GFX and the custom fender flares front and rear to deflect the air around the tires and cut down on drag there.


Obviously the placement of the cooling ducting is just arbitrary for this drawing, I drew it in like that just to give you an idea of what I was going for. If I had my car in front of me to look at, I could have drawn a more realistic routing.

 

The drawings look good. The only issue is the cooling system. You shouldn't double up the heat exchangers, that's just not optimal. Cold air has the ability to obsorb more energy (heat) than warm/hot air. So you don't want the hot air coming from the first heat exchanger going into the next.
A cooling systems design has a LOT of components but some general rules. The one I just talked about is one of them.
The troubles with cooling systems is there effect on aero. Obviously you need air flow but too much and it slows down a car, this is where my reply starts going off topic so I'm going to get back on subject .

Spring rates aren't important at high speeds if the vehicle has no lift and no downforces. The dampers are what's important! Valving a damper depends on (again) a LOT of variables including speed. A perfect example is the inertia sensing dampers. These dampers sence the inertia of the wheel assembly which is effected by vehicle speed. The higher the inertia (faster moving wheel asembly) the stiffer the damper. Vice versa for a lower inertia (like hitting a speed bump at 5mph vs 30mph).
A spring on the other hand needs to be setup for speed ONLY if the car is producing lift or downforce. If it produces neither then the springs should be setup for the natural frequency and pre-loaded for the rest of the course. Compromises must be made to prevent the vehicle from nose diving into the road.

Oh, and another thing, that chin spoiler followed by the belly pan should be more level with each other for stability. If you were going for downforce then it's fine. A good way to create "free" downforce at the expense of aero drag is to put the under-tray (belly-pan) as low to the ground as possible without scraping. A good way to do this is to attach the under-tray to the front LCA and rear LCAs. This way if you're taking a hard left the undertray doesn't scrape from body roll. That's probably WAY out of perspective here but it could be a problem in a racecar.
Last "note" so to speak; Aero drag isn't just the a coefficient, it's also frontal surface area. If you have downforce and wide tires the vehicle will squat and reduce the frontal surface area (tires).

 

Sounds interesting. If you want the wheel to tuck like it is in the bottom picture then guarantee you'll need to pull the inner fenderwell. I just got done installing drop spindles and short springs + weight jacks and I have about the same stance. There is about an inch of travel before the tires contact the fenderwell at my current setting, still goofing around with it. At full lock down the fenderwells rest on the tires (this is 245/40/18).

 

thats one of the reasons alot of all out drag cars mount bars between the "frame rail" and firewall, and connect the strut to that.

then they cutout the fenderwell..


the other reason is access... once the fenderwell is out, you can sit on the tire and do anything underhood.. lol.

 

Thanks for the replies. That's why I drew up that drawing, just to be able to visualize the ideas instead of just trying to explain them. The cooling system was purely an idea I had that I wanted to run past y'all, wansn't real sure if it could actually work or not. I was thinking of something like the GT or the Shelby 1, with dedicated cooling ducts. Obviously there is much more involved with that than just "it looks" good, I just drew up something arbitrary for the sake of discussion.

JPrevost, thanks for the post, very informative. I'll definitely keep the belly pan tips in mind when I try those out.

CrazyHawaiian, one thing I was considering if I ever built an all out race car was to build a tube frame front end that would suppliment the factory frame rails and tie into a full cage. I would use these to reinforce the factory strut mounts, or relocate them higher up to drop the car more.

 

OR.

you could just skip everything, pin the hood down, slap on some good tires and shocks, and drive it really really fast.

and do nothing else.

 

Your basic ideas are correct, however the twin 24" x10" cores will not supply enough cooling. Better to go with a standard sized Aluminium Racing radiator such as a Griffin or C&C cooling.

Box in the radiator inlet on all four sides and I think that you will find that the nose openings will be sufficient.

Be carefull about running the front air dam too close to the ground. Getting it too close can actually make the car too sensitive to " Pitch" . Can stall the air and create " Porpoising" , especailly if you decide to run a diffuser under the front.

A front " splitter" will add a tremendous amount of downforce to the front with no drag penalty. It must be strong though. People generally underestimate the ampunt of downforce a front splitter can make. The result is that the splitter will often bend or break.

When you start building downforce you will have to increase the spring rates.....particularily on the front Keep that in mind ( we're talking Race cars hear folks ).

Also the poster who stated that you don't have to increase spring rates at higher speeds....only dampner rates...has it all wrong. As speeds increase the " Natural frequency" rate of the spring has to increase. The only way to do this is to increase the stifness of the spring. Shocks ( more correctly dampners. " Shock" absorbers are an incorrect North American term) are designed to dampen the action of suspension movement. They ar NOT designed to support the car Nor to absorb " Shocks" .

A regular car has a natural frequency rate of around 1.0 to 1.25 cycles per second. An Autocross car should be from around 1.5 to 2 cps. A race car can be anywhere from 2.5cps up to 5cps ( F1 car ).

Got off topic there but spring rates do have to go up as speed goes up.

Back to aero stuff. One of the absolute best books on aerodynamics is a book called " Competition Car Downforce " by Simon McBeath. ISBN 0-85429-977-7. particularily interesting as it goes into great detail on aero work on British and Australian Touring Cars....very similiar to what we run. Lots of info on Airdams, splitters and front diffusers.

If you choose to run a front diffuser ( recommended ) be aware that you have just changed the complete aero concept. With a diffuser, air MUST be allowed to flow under the car. You are now utilising ground effects and CONTROLLED airflow under the car is how it works. An airdam builds downforce by blocking airflow under the car, thus creating a low pressure zone. But a diffuser setup can make much more downforce by letting some of the air flow under the car and generate a low pressure area under the inverted wing profile. McBeath's book shows in detail how BTCC cars solved the "pitch" sensitivity problems associated with runners splitters and diffisers too close to the ground.

And yes folks...alll this stuff does work. And at surprisingly low speeds( we're talking significant effects from 50mph up ) if done correctly. I knocked 1.5 seconds off my own Hillclimb record this year...all with some fairly simple aero work ( mainly on the front )

That's all I'm going to say on the matter. I don't want to give away all of my secrets

PS: I'll try and scan some pics of my car and some of the front aero stuff that worked for Hillclimbs. May take a couple of days though. BTW....it's 5.00AM here....have insomnia

 

Here's a third gen firebird that went over 300 with a stock spoilerhttp://www.popularmechanics.com/auto...le_salt_flats/

 

Chickenman, I'm going to have to look around for the book, Amazon.com doesn't even show it as available.

 

Yes...but read the whole article. As stated before...Salt runners heavily weight the cars to hold the nose down. This is the only form of Motorsort ( other than Tractor pulling LOL ) that weight is added. Weight is normally a deadly sin.

Throw in some corners, bumps and braking area's and the limitations of a Bonneville design become apparent. You also usually don't have several miles to accelerate all that weight.

And I take it that TexasLT1 is designing a car for Road Racing...so adding 300 pounds or so to the front may not be in his best interests.