Car is slammed track style.

 

LOL! Then you'll have some problem like me!

 

A few of my friends that race 997's in PCA and PBOC use the Vorsteiner wing and the other use the GT3 like aero kit wing.

 

I do like the vorsteiner unit. So it's adjustable? Any ideas on fittment?

 

Fitment should be better than most after market brands...

 

Vorstiener is adjustabkle and fitment is great...it is a quality piece.

 

I do not beleive this to be ture. At all. The rear wing (located behind the rear axle) will affect the front end. Think of it as an heave effect. Place a pen on two supporting points each ~1/4 in from each end of the pen. Then press one end down. What happens to the other? Well, it goes up. English is not my native, but maybe you get the idea.

These cars are obviously very light in the front vs front engined cars. As you all probably know previous generations could be quite an interesting drive on autobahn or fast tracks such as the Ring. Latest iteration is much improved. Porsche themselves and others, teams closely connected to Porsche such as Manthey etc, still strongly advices against adding/increasing rear wing only. For a good reason.
I know there is a racing series in the Us where they only user the rear wing, but I'd not take that as any proof of what's actually a good way to go. (Someone said this was due to regulations anyway.)

You could get an indication of what actually happens when rear downforce is increased by looking at the numbers published by the Nurburgring experts at the german mag SportAuto. These guys use the very same vind tunnel as Porsche used before they built theire own. I beleive it belongs to the Unuiversity of Munich. These figures are for various generations of GT3's at 200 km/h (~124 mph):
http://www.sportauto-online.de/super...3-1345012.html

As you can see the 997.1 GT3 RS are a little bit worse in the front vs regular GT3, -2 kg vs 0 kg. The front ends are virtually identical, the rear being the difference.

Regarding the front bumper there is a small, but significant differences between Aero and stock GT3 bumber; the small vent right in front of the hood wich lets air coming through the center radiator of the GT3 flow upwards above the car => reduced lift. The stock 997 and 997 Aero bumper doesn't have that feature.

 

Unfortunately I'm not a physicist so I can't prove/disprove your hypothesis.

Consider that the assumptions you are making would imply that the downforce applied at the tail result in a change in ride height at the front and this (according to your assumption) results in more lift.

In order for the pencil example to be accurate, you'd need to factor in the two suspended levers and also assume the minute changes in ride height affect aerodynamics. By this logic, different weight drivers would affect downforce as well.

Any scientists here?

 

There was a pretty good article in Grassroots Motorsports a couple of issues back (May?) that discussed aero treatments and they made the same point about balance front-to-rear.

In my earlier post I said more rear wing might create more front lift. This is probably technically incorrect, but I think it is how the car would feel - lighter in the front - and perform - less front grip as speed increases.

The geometry is certainly more complex than the simplified pencil example, but I think the net effect is well described. Basically you have to either have a wind tunnel or go out and test-and-measure each mod to see its impact on downforce and drag. The GRM article gives some tips for doing this without expensive gear.

 

Here is a link for the GRM issue:
http://grassrootsmotorsports.com/iss...=480&width=700

I didn't find the article on-line but I also didn't look real hard.

 

Fasciting! I love this stuff. It's probably more and any of is would ever find useful but I enjoy the discussion none the less.

I think I'm going to use the aero or vorsteiner option. I suppose a cup setup would work well but those cars have slot more power to counter the added drag.

 

this looks like a good article on aero:

http://www.modified.com/tech/0610scc...t_2/index.html

Here's an excerpt:

"To improve high-speed handling, we would normally add downforce in proportion to the car's lengthwise weight distribution. In many front-wheel-drive cars, which have about a 60/40 split, adding downforce in the same percentages to the front and rear retains a balanced handling feel.

If a wing is added to an already 'balanced' car, then the tendency will be to increase understeer because of the slight front-end lift. Since most production-based cars are designed to understeer, the addition of a wing will make this tendency even worse at higher speeds. To correct understeer, the easy fix is to add downforce to the front. A properly designed air dam - with or without a splitter - will add some much-needed downforce."

 

That was Part 2; here's part 1:

http://www.modified.com/tech/0607_sc...t_1/index.html

 

I would not be so sure of that. Even really small differences in angles, radius's etc might have a greate/meassurable effect at speed.

One aspect that often is forgotten is the relationship between lift/downforce and drag. Porsche's achivements with eliminating lift and not, at the same time, increase drag for the 997.1 GT3 are simply phenomenal. Gen2 is even better. I think it was Mr W. Rohrl that in one article said that the steepest setting of the 997.1 rear wing was rarely needed because it mostly increased drag without adding any extra force. Quite a complex field of engineering.

If performance is of most importance, then Porsche OEM is the way to go. If for looks mostly and never driven at speed, your choice might not be that critical.
One can argue that normaly skilled drivers won't feel the difference. Probably true. But, on those (few) occasions the car is driven at speed, it might be less predictable or more difficult to handle at the limit. Interesting or dangerous depends on your personality

Since this is the 997 forum, here are the 997 Carrera figures from SportAuto:
http://www.sportauto-online.de/super...e-1347921.html

Even though the regular Carrera is worse then the GT3, these numbers are actually quite good compared to other performance cars.


A few numbers for GT2 and TT as well:

GT2: http://www.sportauto-online.de/super...2-1354984.html

TT: http://www.sportauto-online.de/super...o-1357306.html

 

Last months Grassroots Magazine (awesome mag BTW) did a feature on aerodynamics. They covered adding a wing to the rear of the car.

Adding a rear wign does NOT product front lift. I have also read about this in Race Car Engineering and Auto Sport.