Geoffrey

I don't know about Jean, but I have flush mounted side windows with a sliding window, so not much air goes into the cabin.

Jean

Although there is in most cases a relationship between drag and downforce, it is not always the case. if you drive with the two doors open you will create huge drag but no downforce. If you increase the angle of your rear aerofoil, you will experience both drag increase and downforce increase. If you remove the undertray, you will increase drag but also lift (air coming from under the car moves upwards through the engine bay, creating upward pressure on the inside of the engine lid, hence lifting the car), whereas if you work smartly on underbody aerodynamics you will be increasing downforce but not drag.. This is one of the key F1 developments to keep the car glued to the track at high speeds because of downforce, while limiting drag to a minimum.

Longer distance over the car seems to improve drag not deteriorate it, at least this is what many of the old race cars, Manthey and Alzen use on their race cars, but also to improve stability with lateral winds, please don't ask why, but it's true

I never have the windows opened when I am driving at high speeds. The rear lexan does bend inwards at highish speeds, I have it flush mounted. My only guess is that the roof flying on MOD's car is as a result of pressure on the cabin by the wind (sideways from lateral wind and frontal from the direction of movement at speed) which expanded the air inside the cabin upwards or sth like that. Poor fitment also most likely.

Felix

I noticed the sunroof lifting on all 3 993tts I looked at at Vmax on 11.11, including mine. They could be pushed back into place between runs. I even joked to Mod500 that he needed to do somthing as he was clearly losing top speed. Little did I know what he was going to do!

Next Vmax I'll log cabin pressure via the DL1 to see what happens as speed increases.

bb993tt

I was one of the three. Took a piece of advice from Alan McKee (formerly known as Weltmeister) and duct-tape closed the air intake at the back edge of the hood and also taped the leading edge of the sunroof. Don't know if that's why my sunroof didn't suffer the same fate at MOD500's but it did give some piece of mind for the rest of the day.

Felix

I checked the air pressure inside the car today; between at rest and at 175 mph there's a drop in air pressure of about 8 millibar.

So sunroofs are getting pulled out by low pressure from outside of the car, presumably coming off the windscreen?

911/Q45

Is that with the windows up or down? (Most tracks require the windows down for safety reasons)

sweanders

In Europe most track meet organizers require the windows to be up for safety reasons.

Open windows screw up all the aero work done.

Felix

Windows up; at 175 mph I prefer them that way!

Stummel

Phelix, care to share any performance results?

Stefan

Felix

Hi Stefan, nothing much new to share. Vmax was 177mph; backing the wastegates off didn't result in any significant change. I'll post some graphs later. Best 60-130 to date is 9.6 seconds.

Stummel

Thanks Felix!

100-200kph is around 8.5?

Felix

8.45!

but I must confess those numbers are from running with a light fuel load and no spare and no passenger seat (so about 50 kg lighter than normal lightest road trim)

Stummel

I am really sorry, no intention to make it look slow

What was the best 100-200kph with the rebuild stock engine?

Jussi

My rebuilt "almost stock" 3.8TS's best 100-200kph time with one gear change was 5.20s

Felix

No worries!

Probably 10.4 seconds but with a full 90 litre tank and slowish shifts (0.6-0.7 seconds). That's with a factory 430 ECU. I now manage them in about 0.4-0.5 seconds without speed shifting or anything of that sort.