bronson7

Does anyone know the actual weight of down force these GT cars provide? We know the Formula 1 cars can produce between 2000 - 3000 lbs of down force and could literally drive upside down. Very interesting topic.

qbix

I would say not much (regular GT3) and it depends what speed we are talking about.

These cars create a lot of lift so the whole aero is to neutralise it and make car stable at high speeds.
I doubt there is any downforce that can help you take corners much faster than let's say regular 911.

JasonAndreas

Engineering Basics - Diffusers

rm21

I continue to learn quite a bit from all the engineers on Rennlist, so thanks for all the thoughtful posts. But it seems like the theoretical debates never really stop. I get it that most of us that want to try aero mods don't have a wind tunnel at our disposal, but it really isn't that hard to test some of these changes in the real world. Stock GT3s get light in the rear on certain areas of a track (the kink on the back straight at Road Atlanta is a great example). Bolt on the mod, in this case the diffuser, and see if it has an impact. If it doesn't, take it off. Am I missing something?

928cs

From a French magazine, downforce @ 300 km/h (186 mph):
- 991 GT3 RS: 350kg/772 lbs
- 991 GT3: 115 kg/254 lbs
- 991 R: 35 kg/77lbs

Make your choice

Bartron

Thanks for posting those up. I'm not an engineer so please chime in if you are. IIRC downforce is proportional to the square of the velocity. Hence, it takes speed to realize the downforce benefit of these designs.

Using this assumption, at 150km/h the relative downforce of the three above could be 193lb for RS, 64lb for GT3 and 20lb for the R. In terms of real world use, I can see that the RS may feel different but I'm curious if you'd be able to tell a difference between the GT3 and R.

bronson7

Thank you 928cs.

CAlexio

rear-engine diffuser:



mid-engine diffuser:

s4corrado996tt

Agreed on RM21's opinion! I really appreciate all who have given such instrumental input on this topic. I will just go head to buy one to see how it turn out to be. Thanks everyone!

Footsoldier

Thanks for posting, but from that list, for performance I'd take the R, because it will be generating a lot less drag. There aren't many 186mph corners in the world, for a road car. (Obviously the d/f will help under braking at the end of the straight)


So, pretty much the 90-100mph that's most relevant for faster corners of a race track I'd say. If RS at 94 mph is 193lb/88kg, then it's not doing much at all

We can assume the R is generating none in terms of feel, GT3 negligible. RS - my guess is it generates massive psychological levels of downforce....

On a non de-restricted road, downforce is not going to be a factor at all. On an autobahn at 180mph plus where it probably helps if there's a bend. Most likely the real reason for a big wing! (+ the racer 'look')

CAlexio

dude.. i thought the gentleman's agreement was not to talk about the emperor's clothes.. how many convos on the downforce provided by the gt3 wing for example have ended in acrimony?.. I mean porsche put an entire BUTTON in the cabin of even the most plebean porsche so they could raise their spoiler at "speed" to make the car perform feel "glued to the ground"... let people "feel" the downforce as they enter the highway on-ramps.. you know how much marketing $$$$'s goes into convincing us of that?

sheesh..

bronson7

You tell him, Alex.

Footsoldier

Sorry guys, I must have missed the protocol briefing. I may have been out driving that day, which shows how messed up my priorities are.

I'm guessing we don't talk about the real effect of the Magnesium roof on the center of gravity either...?

CAlexio

Exactly! We just praise and talk about how much athletic the car feels in corners with the magnesium roof. ;-).

But all jokes aside.. you don't see a bit too much koolaid drinking on our forum?.. a little more critical perspective and less blind love of the brand and its very calculated strategies would do good I think.

Macca

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