Ground Effects anyone?

[Porschekid962]

I know Tyson rigged up a flat bottom for Jack's car but I was wondering, with all the crazy 911's out there, Otto's tube frame racer and the like, why has no one gone to the extent of capitalizing on full ground effects. If so much work is thrown into a tube frame mid engine 911, wild twin turbo engines, chopped roofs on track cars and the like I have yet to see or hear of a ground effects 911. Is it because most of us lack the technical knowledge, wind tunnel acces or ability to create a true ground effects car that is has not been done? Do class racing rules disallow it? I thought POC rules and PCA rules did not allow flat bottoms cars. although a ground effects car wouldnt not be a real flat bottom......

Just wondering, ranting, wishing I had a car to try it on, yes it would require quite a bit more work but the results if done right would be stunning. Just think about being able to run without a rear wing, less drag=higher speeds.

So has anyone done anything besides a flat bottom? Enclosed lower engine area with splitters? Front underwing? Real skirts?

[ttweed]

Originally posted by Porschekid962
Do class racing rules disallow it?

Both PCA and POC club racing rules prohibit aerodynamic aids of the type you are proposing, plus the investment in developing them would be cost-prohibitive for most amateur racing enterprises. A true ground effects car requires body tunnels and a very low, stiff suspension to deal with the downforce and sealing issues, which is more applicable to the center-seater formula and prototype classes, not production Porsches.

Even most pro racing has placed limitations on aero aids ever since Jim Hall's Chaparral in 1966, in the name of safety. A car developing a large amount of downforce becomes an unguided missile when something unexpectedly interrupts the massive grip the driver is depending on to keep him glued to the track.

TT

[Zeke]

All that said, Tom, I believe in air control. Diffusers such as the barge boards on F1 cars could be subtley used under the car in the name of "brake cooling aids."

The air under a production car is quite 'dirty.' 914s had a flap at the bottom of the rear bulkhead to help the air flow down from the underside of the motor where the cooling air was exiting the cylinder fins.

I think the kid is on to something for a discussion.

[JNadal]

a rear diffuser that covers the trans and engine bay would be simple to design and fab up. Using a little logic, you can get 80%-90% of the functionality of a wind tunnel tested one. The only problem is the weight added.

[sammyg2]

I put ground effects on my first 914, oh ....about 25 years ago. It consisted of a front air dam with hard rubber skirt hanging down to about 1" off the ground, rubber skirts just inside the front fenderwells, and reinforced rubber skirts running the entire length of the rockers. It actually helped keep the engine cooler from the negative pressure under the car at speed.
Onliest problem was, it only made a difference at higher speeds. If i had a large sweeper like a freeway overpass I could stick it like glue but that's about the only time it was and good.
Back then I didn't do track time so no telling if it would help there.
it did slow the top speed down noticeably but it was only a 1.7 liter so it didn't have much top end to begin with.

I used to chalk the front air dam to see if it would drag. At anything above 85 mph it would touch the ground according to the chalk.

[911pcars]

Unless you copy something from a proven race car, any ground effects additions w/o the benefit of a wind tunnel or other aero testing is probably equivalent to the ground effects found on most sport compact Hondas and Toyotas skimming our neighborhood streets.

Sherwood

[Randy Webb]

First, I don't know why....

Second, it might not be worth it, considering the characteristics of the "top" body -- the car was good in its day. But, it's day was before numerical modelling techniques were used to crack some solutions in the equations that govern ari flow (these eqns. have never been solved BTW).

Third, it won't be that easy to do anything with the hot engine/exhaust hanging out at the rear....

Fourth, if you try something, how are you gonna test it??

Fifith, don't let me stop you from trying something.

[JNadal]

Originally posted by Randy Webb
Third, it won't be that easy to do anything with the hot engine/exhaust hanging out at the rear....

This is the only physical obstacle. The exhaust would definitely need to be modified.
Once I get my car ready and rolling I am going to make an aluminum or plexiglass rear diffuser and front diffuser. The exhaust I will be running will be heat exchangers with tin cut off and a pipe bolted to each instead of a muffler. If its too loud for me, then I might buy some cheap glasspacks...

Grund effects are a pain in the as to design and make, but a functional rear diffuser on a 911 is simple and could be really effective.

[911pcars]

Not an expert, but for any rear air diffuser to be effective you need a large supply of airflow under the car. The exhaust isn't enough, IMO. That'll require some major surgery to the chassis to accomplish this. Otherwise, you don't want a lot of air under the car. This produces prodigious amounts of sweat on the palms at high speed.

Not that it can't be done, but do you see any path for a couple of tunnels running along the length of a 911?

Sherwood

[ttweed]

Originally posted by Zeke
All that said, Tom, I believe in air control.

OK, I'm with ya on that, Zeke. Air flow management is good. Cleaning up your drag is great to make the car more slippery. Channeling cooling air is a good idea for brakes, engines, etc. Spoilers and splitters to decrease lift is a proven technique for Porsches and many production cars. Leading edge wings in the rear do develop appreciable downforce that will help keep the rear planted in high speed turns and are widely used.

But to me, "ground effects" mean BIG downforce, and that requires tunnels, with inlets, side skirts and rear diffusers channelling huge amounts of air thru a negative airfoil shape in the central portion of the body, where downforce is easiest to control and balance. This would be impractical for a unibody car like the Porsche without tube-framing it and changing to a center-seating position so that the pan could be cut up for the tunnels, and you would still have to deal with that wide-ass flat six in the rear, blocking the exit. The design and development costs alone would empty the deepest pockets, I think, and you wouldn't have a car that would be legal to run anywhere when you were done.

Better to take a little D-Sportsracer and graft some Formula Atlantic tunnels into it if you want to tinker with the idea. Believe it or not, there are some guys here who are doing exactly that, and totally on the cheap (amateur SCCA racers).

TT

[Jack Olsen]

The $29 plastic panel we put on the bottom of my car made it 1.5 seconds faster at Willow Springs. Nothing fancy -- just smoothing out the airflow on a car with an underbelly condenser mucking things up.

I think a diffuser on the rear of a 911 would be a nightmare to work out.

[A Quiet Boom]

Correct me if I'm wrong but doesn't the 2 seater mid engine Carrera GT had a carbon fiber underside containing tunnels? If I remember right it's tunnel have cutouts for the halfshafts to pass through. I'd bet this could be done on a 911 without cutting up the floor since most tunnels I've seen are very shallow in the front to middle of the car. The upward curve could start where the floor ends and the rear seats begin, let the shafts pass through and out the back just outside the valve covers. I'll have to ask my father, a former NASA engineer how to compute where max downforce would be etc. This would be a neat project to say the least.

[JNadal]

Originally posted by 911pcars
Not an expert, but for any rear air diffuser to be effective you need a large supply of airflow under the car. The exhaust isn't enough,

The exhaust needs to be redone to allow room for the diffuser not to add airflow. I think by modifying the rear bumper or removing it, the diffuser would have enough room.

As far as a full on ground effects package goes, no, it would not be possible unless someone wanted to cut the floorpans and make new custom ones with channels bent inward to direct air under the car. It can be done, but who wants to be first!

[Porschekid962]

Thanks guys. I have a few ideas for the rear diffuser and front underwing along with some central tunnels that wouldnt be "TOO" tough to do. The idea of cutting up the car into sections and tube framing some of them is rather interesting but I would be afraid the geometry and the soundness of the structure would be lacking. Unless of course I had access to a 10x20ft steel table jig base and was able to replicate the geometry exactly. I have quite a few drawings of my ideas and cut up some old plastic models and mocked up with card paper the aero package. So where can I find a roller, 69-75, cheap????? Im a college kid with what, no budget hahahaha.

Thanks for all the input, this is why I like this board so much.

[Randy Webb]

college... pasadena... which one? maybe you have access to some engineering assets? think: class prject. ... and it will be a lot easier to do a scale model. you need to alter speed and fluid type (viscosity) to get equal Reynolds numbers and then the model will be as good as the surface details on it....

[Porschekid962]

think art center college of design in pasadena and i am allowed to take classes at that place they call caltech. yes this is actually going to be part of my senior show as well as a tube frame cafe racer with a modern drivetrain to be sold as a kit. oh the ideas. so im hoping to get some funding from porsche since i might get a scholarship from them and move forward on this project with haste. who knows, i wont hear back from them until early 05

[cab83_750]

Originally posted by JackOlsen
The $29 plastic panel we put on the bottom of my car made it 1.5 seconds faster at Willow Springs. Nothing fancy -- just smoothing out the airflow on a car with an underbelly condenser mucking things up.

I think a diffuser on the rear of a 911 would be a nightmare to work out.

Funny!

I reminded me of an article years ago in one of the car magazines. By placing a 'duct tape' over the hood/bumper/spoiler section of a car, the max MPH increased drastically. I also recall it being on a Viper! They titled it something like "the $1.00 performance mod!."

[5axis]

How far could this have gone if it were allowed to continue?
I am sure it was a test of driver faith to believe in the areo traction gods.

david 89 turbo cab

[Jack Olsen]

Originally posted by cab83_750
Funny!

I reminded me of an article years ago in one of the car magazines. By placing a 'duct tape' over the hood/bumper/spoiler section of a car, the max MPH increased drastically. I also recall it being on a Viper! They titled it something like "the $1.00 performance mod!."

We did that, too. Passenger rear view mirror was folded back. Windows were each raised up an inch above the sill. Tape over one of the bumper cooler inlets, the hood duct, and on other irregularities and seams.

[Porschekid962]

probably to the point in which wings were no longer necessary. jim hall told me at long beach he though they were useless at some tracks, he said they mainly calmed drivers nerves and that most of the air at the rear of a CART car was so dirty it really didnt do that much. whether he was giving me a load of bs since i was rather young i wont know until i get into a wind tunnel with a moving floor hehe.

jack good point, it always amazes me at how crude the fit and finish is on most all track cars, pros as well at times. the last poc event at fontana looking at the cars up close they almost appear slapped together the night before.

i revisited an old adrian newey concept about "activated" rear diffusers which would make dealing with a porsches exhaust much easier. i really need a scanner or digcam so i can show you guys where im headed with this. ok its late, time for bed.