Mike A.

The track season is over for me. I drive a track dedicated '89 951. During the coming weeks my motor will be torn down and refurbished. At this time I will add enhancements to significantly increase horse power. I believe I will then need to increase downforce for better handling.
At the present the car weighs just under 2600# with 1/4 tank of fuel. It is lowered about 1/2" below stock and has a full race suspension with coilovers on all four. I use 18" Hoosier's, 245/35 up front and 275/35 in the rear. The downforce I have now comes from the stock spoiler in the back and an A.I.R. front splitter and slightly lowered side rocker covers. I am interested in adding a rear wing.
My concerns are:
1. What shape (straight vs banana) and size (60" vs 70").
2. When adding a wing, should the rear spoiler be removed?
3. Will I need additional downforce in the front if I use a rear wing?
4. Does the rear valance serve a real purpose?Should it be removed?
A forum search on downforce yielded very little info. Anyone have experience with this topic?

Huntley Racing

The wing design is an easy one to answer. The ONLY reason to use a 'banana' wing is if you have a max length limit. Banana wings have the effect of being larger than there length would normaly be. However a strait wing is far more efficient in a lift/drag issue. Don't buy a 'ricer' wing, they are not true airfoils and have very bad lift/drag. A 'real' wing from AIR or GT Racing is the ticket. I have used many fifferent NASA airfoils and found that the GT wing is the most efficient single stage wing us mortals can afford. At zero deg angle of attack the wing makes 300# downforce at 140 MPH! 944 cars like the wing aft of the stock spoiler a few inches and at roof line hight. Either keep the stock spoiler or go with the 'Le Mans' spoiler from GT. The 'Le Mans' has a very good L/D though it looks like it would not. The long front extentions should be removed and the spoiler trimmed a bit on the front section. Deep side rockers are a big help on those fast sweepers. The best I have seen that are not custom made are from AIR.

The lower valence issue is a bit more complex. The 'ideal' is to completely cut the rear trunk out and build tunnels under the car from the front to the back, exiting at the top of where the plate used to be! If you do this then the car can make 2X-3X the downforce of a spoiler/wing combo with littel to no increase in drag! The rear wing must be mounted a bit lower and further back to help scavange air from the tunnels.

I recommend picking up a book or two on automotive aerodynamics before you start cutting!! Good luck.

Mike A.

[quote]The long front extentions should be removed and the spoiler trimmed a bit on the front section.<hr></blockquote>
Derrek,
What are you refering to as "the long front extensions?"
Also what do you mean by "trimming the spoiler"?
I see that GT Racing has two straight wings. They look the same to me. How long is yours? Do you keep it at a zero degree of inclination or do you incline it for more downforce for cornering?
I logged onto the AIR web page...no info on side skirts unfortunately.
I have read up on the issue of aerodynamics. Amoung others, I read "Competition Car Downforce" by Simon McBeath. It helped that I had a year of physics in college.
Although installing tunnels to facilitate ground effect downforce is the ultimate, I'm not prepared for such a large and costly project.

Tim Comeau

Mike, If I can add to Derrek's generous advice........
Keep in mind that if you run with the Porsche Owner's Club on the East Coast or West Coast, the rear under chassis tunnels(diffusers) are specifically disallowed in everything but the Z classes according to the 2003 rules.
<img src="graemlins/nono.gif" border="0" alt="[nono]" /> Paragraph 26.4.2 says word for word, "Any aerodynamic modification NOT LISTED in appendix C (V performance mods)is not allowed. They only talk about rear wings ,spoilers, and front splitters.
Further, it states, "Chassis diffusers and or aerodynamic modifications to undercarriage are not allowed." I hope I didn't burst your dream bubble, but better you know now than find out later after you've torn the car up! TC

Alan Herod

Hi Mike, I guess that means that you won't be down next weekend. If you would have just dropped your car off with Ivan or RPM they would have done all that for you. Your car is GT2?

Mike A.

Tim,
Thanks for the info. I wasn't planning on cutting up the car. Maybe in my next life.

Alan,
Yeah, I won't be there next week , I'm done for the season. I had clutch trouble at Watkins acouple of weeks ago. Throw out bearing and afew other bits and pieces self destructed. So instead of dropping the gear box, torque tube, etc., the motor is out of the car and is at Bodymotion getting "freshened up". David Raines at Powerhaus is honoring the three year warranty he gave me on the clutch kit (warranty ends next week), and will replace the broken parts.
<img src="graemlins/jumper.gif" border="0" alt="[jumper]" />
See you next year Alan.

P.S. Car is GT3.

Huntley Racing

The GT spoiler has long side extentions which are a hindrance to clean flow. You would have to see one to know what I'm talking about. The AIR rockers look like this one our 'HR Red Car'. By the way this car just broke into the 1:32's at WSIR this weekend at 60% boost level (new motor). With another 40-50 HP at full boost and new stickers she should be gettin close to sub 30's.

Neil getting back on after a little sight seeing off track at Buttonwillow



Here is a closer view but cut off a bit, sorry. Thats me squeezing in