Poor Man's Ground Effects -- I need some input

[Bill Verburg]

None of the 964 or 993 Cup cars use the tray. They all look like this

[Mike Feinstein]

I have heard that the 964/993 tray was used to meet a European (Swedish I think) sound requirement. I don't believe that Porsche ever intended it to provide an aerodynamic benefit. Has anyone else heard this?

[Craig 930 RS]

That is exactly what the truth is, Mike.

Again, I just don't see the benefit of the tray with the way a 911 is designed; air coming down off the engine, etc

Concentrate on the sides and esp up front for the greatest benefit.

[Jack Olsen]

All right. Tyson's going to disown me when he sees it, but I'm putting together a bolt-on aero kit today. It will not be streetable, but will get put on at the track.

Pictures to follow. Be warned. I come from the hammer-and-spray-can school of fabrication.

[Craig 930 RS]

Hmmmmm I smell a LOW front splitter........

[Randy Webb]

I smell a bunch of GQ jokes coming this way....

[Jack Olsen]

What's worse, I only had a can of red paint on the shelf.

Here's iteration 1. The side skirts are tacked up, loosely. I expect they need to be fairly stiff?



Front splitter has 3.75 inches of clearance. Lowest point of side skirt is 3 inches above ground.

[Bill Verburg]

I like the front(lower would be better)

Take a hint from the factory, the sides need to come out a lot more

[Jack Olsen]

Hmm. Okay. Next up: boxed rockers.

[Tyson Schmidt]

Jack Olsen?

Nope, never heard of him.

[rcwaldo]

Originally posted by project935
Hmmmm ... I used to have a 911 stereolithography model file somewhere I could use to set up a CFD analysis. Just need to find out where I put my CFD software ...

That would be great if you could find your 911 CFD model. We do racecar CFD and might be able to get some work done on it. Although it is really time consuming.

As an example, our CFD guy did some work on the Subaru 2.5RS. This is the front page of his website, but can be used as an example: http://aerosim-research.com/

Smoothing out a (already pretty much flat bottom) car will help in reducing the draggy nature of road cars, but wont do much by way of creating negative pressure (downforce). Like many others have said, aero cars really need to be low, or on the ground to be effective and MUST maintain steady (as possible) attitude to minimize pitch sensitivity. Flat bottom cars without tunnels tend to be really pitch sensitive, which magnifies the need to control pitch, roll and yaw. Hence the need for uber-high spring rates with excellent damping control to minimize these moments.

The pics of your side skirts look great, and should compliment your front air dam. Some turn-outs towards the rear of your fab'd side skirts can help evacuate and lower positive air pressure.

Great project you are embarking on Jack! Now you need to maximize your G-sums (just kidding about the g-sum comment, kind of an inside rennlist joke)

Chris Walrod

[Jack Olsen]

This BBS is a 'no-G-sum zone,' Chris.

Tomorrow's project is boxed rockers.

[PorscheGuy79]

I am new to the forums with no real useful input to this thread but i think it is safe to say that that is one of the meanest 911s ive seen.

[Bill Verburg]

Here's what the road sees of a 964 Cup

[Yellowbird RS]

Did you tested alredy?
Probably a great DIY track setup.

boxed rocker close-up:

[Jack Olsen]

Here's the boxed version, not painted.

Does anyone think it's important (aside from aesthetics) to continue it on a curve, in front of the rear wheel, pushing the air out from in front of the rubber? I like the simplicity of the current straight version. It only required a single 1/8 inch hole; the other mounting points already existed.

[Wayne 962]

You might want to look at the big green RS book - there's info on the original Porsche wind tunnel RS testing in there...

-Wayne

[Bill Verburg]

Here are a couple of shots I took today at the LRP Club races
w/ this thread in mind






Yes, it is important to continue the skirts to both f/r wheel wells

[Bill Verburg]

#99 was a nicely turned out car, It was gridded in first but it seemed to be at a big disadvantage to Spencer Cox and Co. during the race.

Spencer had a great dual w/ a blazing fast 944t, literally the 944 burst into flames just before crossing the finish line for the win. Very spectacular.

[Mark sP]

Do skirts and splitters actually have anything to do with 'ground effects'?

I have no knowledge or experience BTW, but would have thought that there purpose is more related to reducing the amount of air that gets under the car. I suppose that would in itself reduce lift and drag, but isn't technically ground effect?