Jon Darlington
New member
I had a chance to take some high level wind tunnel data on my car (SWB 912) the other day. With the main aim to baseline the car for lift and drag and also to get some undertstanding of small things that could be changed which may effect both. In summary opening holes on the front of the car (fog lamp covers or horn grilles) increases drag and front lift, although reduces rear lift. With the fog lamp covers open there is an increase in flow to the brakes so this also needs to be considered. Changing the front number plate angle to vertical (it is currently at the same angle as the bumper skin) gives a significant reduction in front lift without increasing drag but does increase rear lift.
The other thing we tested was yaw stability which doesn't seem to be to bad the lift figures do change but at fairly progressive rates so shouldn't have a Audi TT issue in a cross wind at high speed!
This trip was made even more interesting as the tunnel had measure and standard 1968 2.0L SWB 911 in 1969 which gave the below figures:
1968 911 measured in the same tunnel (on the same balance)
CD = 0.329
Combined front and rear lift = 0.275 (96.3 kg @ 130 mph)
My car Baseline:
CD 0.323
Front lift = 0.028 (10.7 kg @ 130 mph)
Rear lift = 0.246 (85.6 kg @ 130 mph)
Combined fronta nd rear lift = 0.275 (96.3 kg @ 130 mph)
Setups tested:
Best drag (Le Mans set-up!): fog lamp covers in place, horn grilles cover, bumper plate angle/height (5mm reduction in Z) change.
CD 0.320 - this is a 9 count improvement over the measure in 1969 (equivalent of 1.93 bhp)
Front lift = 0.005 (2.5 kg @ 130 mph)
Rear lift = 0.252 (87.7 kg @ 130 mph)
Best lift:
CD 0.329
Front lift = 0.005 (2.5 kg @ 130 mph)
Rear lift = 0.238 (82.7 kg @ 130 mph)
So setup (what I am going to run?) - I think best lift as the extra brake cooling is a good thing for road rallies and track work, also long runs at v.max are unlikely!
The other thing we tested was yaw stability which doesn't seem to be to bad the lift figures do change but at fairly progressive rates so shouldn't have a Audi TT issue in a cross wind at high speed!
This trip was made even more interesting as the tunnel had measure and standard 1968 2.0L SWB 911 in 1969 which gave the below figures:
1968 911 measured in the same tunnel (on the same balance)
CD = 0.329
Combined front and rear lift = 0.275 (96.3 kg @ 130 mph)
My car Baseline:
CD 0.323
Front lift = 0.028 (10.7 kg @ 130 mph)
Rear lift = 0.246 (85.6 kg @ 130 mph)
Combined fronta nd rear lift = 0.275 (96.3 kg @ 130 mph)
Setups tested:
Best drag (Le Mans set-up!): fog lamp covers in place, horn grilles cover, bumper plate angle/height (5mm reduction in Z) change.
CD 0.320 - this is a 9 count improvement over the measure in 1969 (equivalent of 1.93 bhp)
Front lift = 0.005 (2.5 kg @ 130 mph)
Rear lift = 0.252 (87.7 kg @ 130 mph)
Best lift:
CD 0.329
Front lift = 0.005 (2.5 kg @ 130 mph)
Rear lift = 0.238 (82.7 kg @ 130 mph)
So setup (what I am going to run?) - I think best lift as the extra brake cooling is a good thing for road rallies and track work, also long runs at v.max are unlikely!
