Sigh ..

1 : ian : you can put air under the car .
2 : Scott : it can’t be done !!
3 : ian : it can be done and is done .
4 : Scott : ok , it can be done . But I’m still right . Because race car !!

Race car, production based race car. It can't even be discussed without knowing what the regulations are. Under body down force is usually controlled pretty strict.

Unless you sit on a million dollar wind tunnel, keep the air from entering under the car.... especially a 911 is very unsuited for ground effect due to the engine placement.
Sure, a small diffuser can be fitted, but it must be able to "suck away" more air than enters at the front, I'm guessing the air between the ground and splitter is plenty.

This thread is now quite off its topic.

Off topic enough that you needed to reply with things already discussed ?
Op isn’t asking about a production based race car anyway , merely a Sunday driver . Unlikely to even see any classic lemans 2.8 Rsr type action etc :D:D:D

Magnus - same car about 10 years later, with wing in rear, a 1 added to the number because I tended to register late and someone else got the 99, new front bodywork due to a crash, improving things a bit second time around. I'm obviously not the craftsman Scott and a lot of others are, but when I did string testing and videoed it, the strings looked like they mostly were nice and straight and parallel where you would expect, and whirled around where there was turbulence no little tweaks could reduce in any obvious way - like around the roll cage members.

I had considered race engineer Caroll Smith's advice - the front spoiler opening is X square units, the ducted radiators are a percentage larger than X, and the exit over the hood is a bit larger than the X square units of the intake, but smaller than the radiator(s) - this slows the air passing through the radiator, improving the heat transfer. I've seen guys put a Gurney on the front edge of the hood cutout/exit to further help the air out.

http://forums.pelicanparts.com/uploa...1631778651.JPG
http://forums.pelicanparts.com/uploa...1631778651.JPG

As to the rear tea tray spoiler vs the wing, I can't say I noticed a difference, but it looks racier. A friend once mounted his wing with quick pull pins, ran a couple of laps, then pitted, friends removed the wing, and back he went for a couple more laps. He said he couldn't notice a difference, though this was at Arroyo Secco, a short and rather low speed track in the New Mexico desert.

If I had shock potentiometers, I could quantify downforce, and measure things like what wing angle is best (though cut and try can work there if it is adjustable), and which spoiler or wing is better than which other piece. But I don't have those nice items.

On the off topic subject of air under the car, some race cars have side skirts to try to keep the air which gets under the car to stay there until it exits out the back. Clever ones are some kind of stiff and flexible material which can abrade on the track surface to where it no longer rubs. I think the idea is that air escaping out the sides behind the front wheels is turbulent, and disrupts the much larger flow along the sides of the car, inducing more drag than otherwise would be the case.

Yeah, you probably need some higher speed corners to note any difference. I don't run on many tracks with 60+ mph corners.