rs10

Yes, it probably seems I wasn't paying attention. I was actually paying very careful attention. I just somehow missed about 10 VERY interestig posts (which I've just now noticed) ... .

Anyway, thanks much for letting us know! I read your thread, and it sounds pretty clear this helped keep your brakes cool. And where to cut is pretty clear from the all the pictures you posted. (Basically the same area that's cut away from the first to the second GT3.)

One more question though - the 90 degree vents, what are those, exactly?

Thanks again!

rs10

By some accounts, it cost the car around 30 mph. R&T was able to get a winged Countach up to 155. Without a wing my understanding is that the ~455hp 5000LP really could exceed 180. Making it clear to all the Lamborghini guys had no idea what they were doing.

Except that they did. Indeed, they appatently knew exactly what they were doing. The wing was created by one of their largest dealers, and it did create downforce, a lot of it. Which was the last thing you wanted on a 180 mph, rear engined car with front-end lift. So the clever guys at Lamborghini tilted the wing so agressively that it created almost no downforce at all. It was basically just a big air brake. And they refused to sell it to you. You had to buy it from a dealer.

rs10

Thanks, first of all, for the very interesting posts!!

There are of course many differences between Carreras and GT3s, though if a Carrera has the aerokit, the shape of the front end is very close, possibly identical if it also has a third radiator. With the stiffest of the sport suspensions (X71? I can never remember the name), the ride height is just 5 mm higher, if I recall correctly. Many Carreras also use the same size wheels and tires, the same brake ducts, and the same brakes.

On the other hand, the most interesting comparison may be between the MkI GT3, which didn't vent into the wheel wells, and the Mk2, which did. What else changed? It seems the old radiator vent was blocked off on the MkII, and if one does this mod, presumably one should also block this off. That may have been the biggest change Did the bumper shape change much? It changed, but I don't remember a big change off the top of my head other than the headlight shape, which I would see mainly as a change in where the shape was metal and where glass, rather than a big shape change. Yhough I haven't looked for quite sime time, so this may be nonsense ... . If it's not nonsense, than venting into the wheel wells might account for a significant portion of any front end improvement.

And I think small improvements in front end lift can make a significant difference. The 996.2 Carrera only has about 24 kg of front-end lift at 200 kmph,, so probably about 44 or 45 kg at vmax. The MkII GT3 has 13 kg, and I believe the C4S has roughly half as much as the Carrera. (All according to SportAuto wind tunnel tests.) By all accounts, the front ends of these cars feel more stable/precise/tied down at speed. And according to SportAuto, the vents into the wheel well was the aero highlight of the MkII versus the MkI. Alas, I don't have the numbers for the MkI handy, and this may be because I never saw them. I seem to remember I could not find SportAuto wind tunnel tests for it.

Oh, and the front vent above the third radiator on the GT3 RS? Contributes about 3 kg of downforce. It's certainly possible that without this the car would be unstable, however. Because without it, it would have almost as much front-end lift as a Carrera.

Anyone know how much front-end lift a MkI GT3 generates??? If someone has or knows where to find the press/launch materials ... .

rs10

And spend the money, I fear. Or these gauges and pots, are they affordable, like, say, an extra heat sensor for a data logger? Is there some software I can use to collect date from them on my computer, or perhaps an app for my phone? This mod is one of several aero questions I'd really like to know the answer to.

Thanks!

docmirror

I suspect that the downforce, and/or speed reduction were often a result of the installer. With the wing in a neutral AoA, the speed would show little compromise, and the downforce very limited. One could of course increase the negative angle of attack to create massive downforce, and huge speed reduction. It's been a lot of years, but I recall someone who knew what they were doing getting it setup for modest speed cost, and modest downforce, to basically minimize the effect where no downforce was really needed, as you mention, and as I alluded to in the rest of the unquoted post(30Lbs of downforce on a mid-engine car is useless).

Perhaps the good folks at R&T, like everyone else in auto publishing don't know squadoosh about aero affects, and set the AoA where Lambo dealer/installer told them to set it, or left it wherever it was when they got the car. I really don't know.

himself

On my car, they were right behind the radiators venting air downward before the wheel housing. That is, air passed through the radiators (and AC condenser) and a big piece of plastic vented the air down to the ground before the wheel well. They were easy to take out.

-td

docmirror

One more thing not considered in this mod so far, is the adiabatic affect of the air. As it's heated when passing through the rads, the air becomes less dense as it is hotter. Ideally, like the Daytona coupe, and my Ferrari Mondial that hot air would escape going up over the front of the car and not down where it will possibly create a pressure bubble inside or under, or around the wheel well(hard to say, without smoke/thermal testing). BTW, someone mentioned ducting it toward the brake intake duct? Not a good plan with warm low density air flow. Aero mods are tricky.

rs10

I understand there are no hard and fast rules, but if there is an answer that is usually true, would you expect switching from 205 section 17s to 225 section 18s (both with almost exactly the same diameter) would exacerbate or reduce this problem?

Thanks again!

rs10

My guess is that the R&T guys simply took the car as it was handed to them, so probably with the standard wing with the standard installation as "fixed" by Lamborghini.

Mike_A

Not to hijack this thread, I might suggest that there is a lot of general technical knowledge with regard to vehicle aerodynamics available, in particular the treatment of exiting cooling air flow. See "Racecar Aerodynamics" by Joseph Katz for instance. Reinforcing some of the comments above, Katz' discussion of wings will reveal just how silly the Lambo folks were (as well as practically every street car manufacturer is) in the uneducated placement of rear wings. Placed within the disturbed air flowing over a chassis, a wing doesn't provide any performance improvements (Read the first part of that sentence before you disagree). Obvious differences between race cars and street cars aside, Katz explains how, when it's placed properly in conjunction with underbody design the wing can act more as a "lung", drawing and accelerating air flow under the car, where more force is created and distributed to the 4 corners, not just 2. More recent performance street car design seems to have caught on.

rs10

I just noticed something very interesting in this photo of the vents on a C4S (page 3, post 41). Am I correct that the vents point outwards? If so, they seems to have been designed not to cool the brakes, but to expel the air from the wheel arch. Maybe, if the Porsche guys were really clever, this even has a positive effect on the other air that is (or otherwise would be) in the wheel well. Anyway, as the purpose apparently isn't brake cooling, it must be drag, lift, and/or, just possibly, helping draw more air through the radiators.

Probably doing this mod the Pelican way wouldn't work quite as well, since the air would not be directed in any particular direction. The best way would probably be to us C4S (or 40AE or Turbo) wheel well liners, provided they are compatible with the neigbouring parts.

Shame we still can't be sure this would have aerodynamic benefits on a Carrera, given the different bumper openings, ducting, and slightly larger radiators.

(And there remains the question whether the GT3 method, on a car with a very similar bumper, ducts, etc., just improved brake cooling or also has aero benefits.)

P.S. Sorry not to include the photo here. For some reason it does not reappear when I reply to the post

rs10

Understanding that 997 Carreras also vent air into the wheel wells, anyone know if they also direct air outwards as on the 996 C4S, Turbo, etc.? Or do they direct it at the brakes, like on a 996 GT3? Or perhaps something completely different ... ?

Thanks!

strathconaman

I heard this,

And thought this:





and got all .

wildbilly32

RS: Don't know about the 997's but the C4S vents are definitely directed out of the wheel well and do not appear that the air flow would have any affect on brake cooling.

wildbilly32

Strath: That would probably affect aero as well!