jorj7

I don't think this is very accurate. It looks like they got the numbers for
the S4 and used that for all models...

heinrich

I think one of the best improvements (and after pulling my rear bumper cover, I believe it is TOTALLY feasible) is a Kamm Tail, because there is actually enough space under the rear cover to hide a bull. Another immense improvement, well within our reach, is a full bellypan with Vette-style outlet fins at the rear. I do not believe that exhausting hot air from the engine bay under the car, is a good idea. Exhausting it to the windshield is probably not a great solution either because it will lead to filth being deposited over the windshield and roof and rear on an ongoing basis.

I do agree, venting the under-hood high pressure stuff upwards or sideways, is the best solution.

jorj7

For my car I've been using .32 Cd and 20 sqft, that taking into account lowering, front air dam, no
mirrors, modified wing angle, different body angle, covering lights, taping, and only slightly wider tires...
Not really exact, but it seems to fit my calculations so far.

mark kibort

I see no increase of material, or stuff, on the windshield vs no hood vent. I have done the tufts test and they point up out of the vent at 100mph, kind of interesting. You cant vent at the base of the windshield as it is a high pressure zone, only slightly lower than the nose of the car area.

Hood vents work well, and they look cool if done right.

mk

jorj7

I also think a Kamm Tail would help a lot, as well as a full belly pan. I've been thinking
about extending the belly pan on my car, but the Tail is a little beyond my resouces
at this time. Maybe someone can make a rear bumper replacement that would
incorporate this.

Also, so far the hood vents haven't added debris onto the windshield.

LightStriker

Question like that... I understand the lower the pressure under the car, the better it stick to the road.

So, why people aren't using wheels as turbine to suck air out of under the car?

atb

My father-in-law's thinking was that the low pressure area at the rear of the roof is double that of the low pressure area on the hood, maybe he was surmising that extra vaccuum would compensate for the extra distance to get there?. He also felt that releasing the pressure at this point would help maintain the laminar flow over the hatch. We're talking points 23-24.

IcemanG17

I want to say the true S4 frontal area is 21.28sqft..but the GTS should be "slightly" more due to its wider stance in the rear...

atb

It would be nice to see a well designed rear diffuser for our cars. I think any full belly pan should be vented and ported out the top or side of the car to release any high pressure spikes, you don't want this happening to you.

RKD in OKC

The full underbody pan rule is why Porsche quit racing the GT1 cars. Before the rule they didn't have pans in the rear under the engine.

RKD in OKC

How about port holes on the side of the fenders like a buick? or maybe those modern aero kit side skirts that pull air from under the car.

Louie928

Hey Adam. Just open the sunroof. Lots of negative pressure there. Cut a big hole in the firewall to vent the engine compartment into the passenger compartment and there you go. Hot air right out the top. Just wear a cool suit and you'll be fine.

atb

I know I left that propeller beanie around here somewhere....

RKD in OKC

Don't need to cut a hole in the firewall for the open sun roof vent thing, just remove shifter boot and insulation.

heinrich

Looks to me (correct me?) like the pressure at the roof and down rearward are significantly higher than anywhere on the hood, till it gets down way back to the base of the rear window?