Berra

I wish I could drive a regular turbo body at high speeds to compare with my Aero kit one. I've been at over 190 mph with mine and it was rock solid. That aero kit must be doing its thing!

It's said that 911's are known to be light up front when going really fast and I'm no racing driver but I didn't feel anything when going that speed.

squid42

One way of measuring downforce of a clearly identified aero piece like a wing is to put piezo elements into the mount. If the thing sits on something that has a hinge on one side and then some rubber stops on the other side then putting piezos under or on top of the rubber will do.

Piezos are electronic elements that generate a charge under pressure. You just measure the voltage on the output and you get an indication of how much pressure is applied.

The output is highly nonlinear and generally messy, however that does not matter in the case of a wing. While the car is standing you can just calibrate the output of the piezo by putting known weighs on top of the wing.

rs10

There are lips like that for the GT3 front bumper, and it's not uncommon to install them on a Carrera. I've been thinking of doing that or adding a Turbo bumper. (Not a GT3 bumper, as it sits too low, and I'd destroy it on speed bumps, etc.) I've also been thinking of adding vents to the wheel well liners, as on the TT, to redirect the air exiting the radiators.

Each of them would probably help, but I don't know how much impact they would have, so I don't know how much lift I'd need to remove from (or downforce I'd need to add to) the rear to keep it balanced. And while I do know roughly what a GT3 wing does for rear lift/downforce (or at least I think I do, because I assume the tiny vents behind the wheel wells can't do much) I've no idea what a duck tail does.

T10Chris

Venting the radiator air into the wheel well in front of the tire like the TT does may hurt more than help.. Then again Im not sure how the Carrera vents the air.... Better to do it as the GT2 does and use the side radiator air for brake cooling so you at least get some benefit. Venting the fender to extract air like 991 GT3RS in combination would be the best setup.

Carlo_Carrera

I wouldn't worry about what might happen at the back just yet. Focus on getting the front to feel the way you want than assess how the rear reacts. That is how the pros do it. Start at the front.

If I were you I would begin by adding an aero front lip.

rs10

I certainly understand your uncertainty about whether it makes sense to vent the air like the TT does. In fact, after learning that Pelican recommends a similar mod to reduce lift, I was so skeptical that it's a good idea to send extra wheel into the wheel well that I started a thread on the subject. But after a lot of helpful posts, I'm pretty convinced it works. As you may have noticed, the air isn't vented straight towards the tire. Rather, it's directed outwards. And it's not just the TT that does it, it's also the C4S and 40AE, plus the 987 and 997.

The reason it works may be that how the 996 Carrers vents the air is less than ideal: It is send down towards the ground in front of the wheel well.

On the other hand, I'm not sure GT2 style venting is for me. It seems to me that Porsche aimed for optimizing lift and drag on the TT (and 997, etc.), but for optimizing brake cooling on GT2s and GT3s. And my priorities are more towards lift and drag.

rs10

Thanks, undoubtedly good advice, and I will probably do so.

While if I end up measuring lilft and drag I'd probably measure every change I make, it's the rear end that would be my main motication for doing so. I'm 99% sure I will want to do something with the rear. And while I know a GT3 wing would probably work well, I'd much rather have a ducktail if it would reduce lift even half as much, provided there wasn't much of a drag penalty. But it seems no one has a clue what effect a ducktail really has ... .

T10Chris

If that is how it vents on the standard 996, then the 996TT/C4S way is better than that method- it is never really a good idea for lift purposes to divert air to the undercarriage that would not have flow under there to begin with... Removing air from the undercarriage is the goal... The lift reduction isn't coming from angling the air outward though, those little vents aren't going to do much to get the air out of the wheel well.. Just going to add to the turbulence already existing within the wheel area at high speeds. Better than shooting it straight at the tire, sure I could see that. I see it as reducing lift, but possibly carrying a small drag penalty, or at best no effect on drag. There is a lot of unknowns with wheel well airflow with a tire in motion.

The GT2 isn't giving this advantage up though, it is doing it in a more purposeful, hit 2 targets with 1 shot kind of way. Instead of wasting the airflow into the tire area where it may or may not create more drag, it is using it to cool the brakes. Still not being dumped into the undercarriage where it could create lift though.. this may or may not have a positive or negative effect on drag compared to the TT/C4S way since it is not introducing more air to the front of the tire rather into the center of the wheel.

Probably no way to quantify which method is producing less drag, if there is even a difference at all, but both ways reduce lift and one also cools the brakes in the process.

The GT2/3 cars tend to take everything performance focused the non-GT cars do, and do it better in every aspect... definitely does not give up any aero advantages IMO. I think Porsche just does not forsee the typical TT buyer needing the extra brake cooling that a heavily tracked car would need so it saves some $$$.

Short version: Now that I know how the standard 996 cars vent the air, this would certainly be a way to reduce lift.. not sure how much. Just not sure if it does anything at all for drag, in either direction.

Carlo_Carrera

I am big fan of how a duck tail looks.

As for what it actually does you are correct. No one outside a few Porsche engineers really knows. And even those engineers would admit that aero tweaking is still a bit of a back art, magic.

T10Chris

Ducktail design on its own sort of works on the same principle a gurney flap/wickerbill rather than as an actual wing, think of the length of the downward sloping portion of the car/entire underbody area as the chord length.

Same principle as the 986 active wing thing that comes up, similar effect. Slows down some of the air from re-entering the flow behind the car/breaks up the wing shape of the car body.. the air coming from under car exits faster than top.. This is all assuming best case/perfect world type of scenario. Ton of other variables play into it obviously.

Fishey

So, I guess everything I have ever learned in car design and professional racing is wrong because venting air around the body can absolutely create "Downforce" or numbers in excess of the natural state of gravity on the body. In fact some of the most aerodynamic cars in history had very little in the way of external bodywork to create "Downforce". The way they created it came without a drag penalty because its the lack of air that has created the "Downforce" which of course is really Suction not pressure doing the work. Fender Vents, Front Brake Ducts can both be used to create low pressure zone under the car adding additional downward force on the chassis.

A Prime example of brillant aero is the Eagle Mk111 which of course is an absolute monster of a car. As seen in the photo its aero numbers are 6431 lbs @ 200 mph, with 1286 lbs. of drag.

Carlo_Carrera

Yes, you are talking about ground effects. And yes as I wrote in another post those systems are very efficient at generating downforce but there is a small drag penalty involved in those system. They do produce some drag.

Funny you should post those Toyota GTP cars. I am friends with the fellow who was the manager of that team during their domination of that series. They were truly amazing race cars.

T10Chris

As sorta on topic but not really, since we've been talking about aero...

I removed the GT2 blade and drove my car with just the "ducktail" for a couple hours yesterday... I had things apart to do some adjustments and a friend called me to bring my car over to go for a drive and dinner... I didn't feel like putting the whole wing assembly back together. From having GT2 blade, to no wing just just the duck tail... Very noticeable loss of stability, rear end moved around a lot more. Not really much difference on throttle since I wasn't driving like a complete lunatic, but even at a spirited street driving pace it was noticeable when lifting off and braking. Didn't like it at all.

rs10

Very interesting, and while not surprising that it didn't work well, it's surprising it was so bad at the speeds I can imagine you reach on the road near Bellevue. I understand there's something in the owners manual saying it's unsafe to drive at speed if the wing won't go up, and with just the ducktail, it would be very similar, but worse.

Hopefully the 997 sport classic duck tail, which is much bigger and more angled, works somewhat better!

Carlo_Carrera