Porsche Enthusiasts Club Forum

Hi

I was wondering what people knew of the aerodynamic benefits of the side sill trims on the S2? I know Porsche have always been pretty clever with their aerodynamics - I am mindful of something Jon said a while back about the great difference he experienced when running a 944 Turbo without the third section of undertray....

Do you reckon these side trims add any ground holding downforce. Trouble is I hate the way the front bits collect all the crap this time of year on the wing bottoms and quite like the clean look of those cars running without them

Jon said they do. But I would think where talking lap time differnces. You could bond them on, seal the eage between bottom off sill and top off trim. Should help with rust last lip for drip would be plastic.

Just make sure it keeps the drain hole open

You don't get the drastic difference in driving above 100 mph that you do if the undertrays are missing and I have never done a back to back comparison like I have had to many times on 944's missing undertrays (looking for leaks etc)..

However, the important thing to remember, is if they tidy up the air, not even be air tight, but just tidying up the air under the car, stopping spillage of air between the underbody and the turbulant air rushing past the outside at 100+ mph, then it may make a difference.. it could be quite a big one.

But then you also get into ground effect as well, which plays a big part in things.

You might imagine that these would have to be airtight and seriously strong to make a difference, but its important to remember that there are a lot of square inches under a 944, and even if these trims just make a 0.5psi difference, but multiply that difference by the square inches of real estate under the car, that is a reasonable, free of charge, difference in downforce, which on the straights might make the car more stable, and in cornering will help no end.

The golden rule is that downforce is pressure on the tyres for free... weight is pressure on the tyres which wants to remain in motion in a steady state.... a 20kg lighter car, versus the same lighter car with 20kg in extra downforce, the second car will be faster in every way, especially if the downforce is caused by ground effect or a reduction in pressure under the body, rather than by the use of a big spoiler.

Thanks, so I conclude that on the basis that 'every little helps' especially on those over 100 occasions *cough*cough* I shouldn't be thinking of getting rid of them - in fact I ought to be looking for a third undertray section too, as I remember Jon saying that the higher the speed the more planted it makes the 944 feel... My S2 was never fitted with one.

I hate the way my current set up can make things feel a bit vague at speed

Cheers

It all seems to help, as I said, I have not really tested a car back to back, with and without the side trims, but I have with the under trays on a regular basis over the last 20 odd years, usually as post work test to check out for engine leaks, and the difference is very noticable, especially as I said, over 100 mph when the difference becomes quite dramatic, even in a straight line... normally what is noticed is that the front end lifts more and if you look down the drivers side bonnet edge, you can even see the bonnet lifting in the middle.. quite worrying really!