pete95zhn

I've searched, but couldn't find a definitive answer. So, does any of you have answer to this question, preferably with pics too:

Is there an under- or overpressure in front and rear wheel wells? The car in question is a 911 ( 996 ).

multi21

I think Mark Kobort had some drawings a few years ago re aero and pressures. Have you tried searching?

claykos

In the wheel well, especially in front of the tire will generally be high pressure. That's why you see cars run louvers in the front fenders to let the air out of the wheel well.

mark kibort

I cant remember, but the wheel well, if not fed via the front of the car is slightly high pressure, but mostly ambient. (certainly the front of the tires i high presure ) the thing about fender vents, is that they are in an area of very low pressure, so it flows air up out of the wheel well, that is fed from under the car, which adds downforce.

JackOlsen

Old tub:

mark kibort

what are we looking at here. air speed across the surfaces areas?

pete95zhn

Thanks for replys!

bobt993

Pete,

My experience with the 993 was to get air in and out. I recently changed front bumpers to an GT2 EVO bumper versus stock/RS splitter setup. In doing so I spent the time to fabricate diverters out of sheet metal that collect the air and exit it out the side of the front nose. The effect was enormous on high speed sweepers. The car could actually be driven WOT in a kink that normally required a good lift or left foot braking. Apex speed on two very fast corners improved 5mph by removing the dirty air. The track I tested on produced consistent times 2 secs under the track record for my class and that was confirmed when I secured the track record in a race the following week. The 996 has better stock aero. If you removed the fender liners to make tire room then you should look at getting that put back in somehow. Aero is a dark art at best. A lot of testing and data will yield results.

pete95zhn

My main issue is to know if the pressure in aft upper part of the rear wheel well is higher than at lower aft corners of rear bumper. So far it seems to be so. Increasing rear downforce by venting to that direction is just a happy by-product...

mark kibort

Its hard to say. a lot of things are going on at the rear of the car, and in the wheel wells.

chris walrod

Essentially a CFD problem solved by software showing the pressure differentials as denoted by color.

Here are similar plots with airflow sim's

mark kibort

so , as you can see, the pressure around the wheel is fairly low ambient pressure, would be flowing out from the bottom of the car, through the wheel, front and rear. obviously, the front of the tire, facing the air flow, is high pressure, like you would see at the nose of the car. in the wheel well, there is a high pressure build up, do to the rear of the wheel well acting like a parachute. this is why venting the rear of the car is beneficial. it releases this stagnant air to the rear of the car to reduce drag.