miky360

I understand that everything is about balance but I don't have the funds to do all the aero at once. Where do you feel I should focus on? Rear downforce or front end downforce? I feel now with my GT3 bumper that I may be too front end biased and oversteer on certain corner where i never used to.

Jean

I am not sure which front bumper you are using, but the 991GT3 has less front downforce than the 991TT in performance mode...

991.1GT3 Downforce@200 kph: Front 14Kg, Rear 29 KG--
991.2 GT3 @ 200KPh: Front 19Kgs, Rear 42Kg with wing at 5 degrees position
991.2 GT3 @ 200KPh: Front 16Kgs, Rear 53Kg with wing at 9 degrees position

991TT @ 200KPh: Front 20Kgs, Rear 40Kg in performance mode
GT3 has better drag coefficients however.

miky360

Oh interesting! Im using the .1 GT3.

Are the RS models producing more front end downforce due to the louvers and flaps?

Pdtp#16

Jean,

your a madman!! Love this data.

Do you know what the 991.2 Cup front bumper with Porsche Motorsport canards generates in downforce. Are you modeling these or you have the data?

been looking all over. Trying to figure out delta between this setup and 2RS setup with the two small canards.

Jean

It is mainly the louvers, according to Porsche they double the front downforce. The dive plains are mostly used to balance the front, they do increase downforce somewhat but also drag, not as efficient as the louvers or the diffuser.

Jean

Racing cars downforce data is not usually shared by Porsche. The canards direct the airflow around the body of the car but are not efficient devices..

It is difficult to dissociate elements, on the GT3R, the mix of front fender louvers, large splitter, canards, air exit through front trunk and addition of a guerney in the front wheel well nearly doubles the front downforce vs. the Cup car from what I have been told by a very trusted source.

The rear diffuser and flat bottom are the most efficient aerodynamic parts, i.e. maximizing downforce with very limited impact on drag.

2fcknfst

I had always been curious as to what the impact of the aero was. Thanks Jean, very informative.

GT2Driver

Many thanks Jean, very informative😊

Jean

2fcknfst, Gt2driver

pfl

Wonderful post! Thank you for posting the data!

I’d be interested to see how large of an increase the 991 TT/TTS factory offered Aero Kit offers.

Jean

Some additional data that could be of interest to some..

So I mentioned that the GT2RS has a total Cl of ~ -0.35 which gives a total downforce of 49/93 KGs= 140Kgs ( ~310lbs) at 200kph.

The Manthey high downforce kit has increased the downforce to 70/200 Kgs= 270KGs (594 lbs) at 200 kph reaching a coefficient of Cl = -0.68

At max speed that's a downforce of 1700lbs for the GT2RS MR vs 900lbs for the GT2RS
Downforce GT2RS MR vs. GT2RS = +93%

Changes were a different front splitter with Cup car flat floor, 2 small front canards each side, the rear uprights were modified 2" higher and seems they did a subtle change to them to be further leaning rearward. The rear wing span was increased slightly (I suspect to 300mm instead of 280mm), end plates larger, and they fitted a larger diffuser ( I read somewhere it was the 911R diffuser modified). I am not 100% sure about how precise this info is, but pretty close.

I am moving in that direction, GT2RS front bumper and rear decklid being fittedbut I am changing the GT2RS wing for a larger one and customizing the uprights to my requested sizes. The new rear wing provides a downforce up to 200Kgs @ 200kph depending on its setup, also adding a custom sized rear CF diffuser. Upfront, a front splitter extending about 4" ahead of the GT2RS front lip and a pair of 991.2 Cup canards. It should all be fitted and tested in time attack mid February. Hoping it will not be a fiasco!

onfireTTS

The above makes me question the accuracy of the Saleen S7 claim of 2850lbs of down force at 160mph. That seems excessive without a rear wing.

Bruce H.

Very exciting, Jean...hope it all works out and takes you to the next level!

onfireTTS

For comparison, the 2019 ZR1 Corvette Big Wing Model was rated at 900-1000 lbs of down force at top speed. 200ish mph.

2fcknfst

Hopefully Jean, when this is all built and sorted, you can post a couple of pics of it. Very impressive, thank you.