Any reason not to vent the radiators into the wheel wells (said by Pelican to reduce
#46
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!
#47
Not to be outdone, Lamborghini fitted a ginormous wing to the Countach in version 2 or 3(can't recall). It had the effect of slowing the car down about 6-8MPH at top end, and provided less than 30Lbs of downforce to the back of the car. Looked absolutely fabulous, was counterproductive. But - 80% of the people who ordered a Countach got one with the massive wing.
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.
Last edited by rs10; 01-04-2017 at 06:14 PM.
#48
if the gt3 exits into the fender wells when the carerra does not then I am absolutely certain that porsche did a boatload of other small but significant things at the same time to deal with the new profile and get the air to go where they wanted and do what they wanted it to do.
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 ... .
Last edited by rs10; 01-03-2017 at 06:41 PM.
#49
5) can you measure down force ? sure . strain gages or shock pots. strain gages if you have push or pull rods or shock pots to measure deflection at speed.
the bottom line is that all your questions have knowable and quantifiable answers if you are willing to do the work.
the bottom line is that all your questions have knowable and quantifiable answers if you are willing to do the work.
Thanks!
#50
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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. Exactly. Apparently. 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.
Except that they did. Exactly. Apparently. 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.
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.
#51
-td
#52
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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.
#53
a rotating wheel inside a fender makes that area a hi pressure area... ... I spent a lot of time venting and creating extractors for the wheel wells to get those pressures down. that's why every prototype you see has vents on the top of the front wheel arches and the rear sides of the bodywork cut back as far as the rules allow.
Thanks again!
#54
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.
#55
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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.
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#56
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
#57
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!
Thanks!