viperbob

OK, those of you that know me already know that I am a bit crazy. Well after continually increasing power in my car I find that I can no longer use the front wheel drive system. As I gain more power, the front tires are being called upon to lay down too much power and turn too hard (I am using Yokohama race slicks that measure 265) at the same time. This results is GREAT understeer. I have had to counter with less and less front sway bar stiffness, more rear bar stiffness (I am now maxed on both), increase of front negative camber to -3 degrees, and increased the rear springs by 200 lbs (currently at 1200 lb/in in the rear). And it still pushes and I want more power... So I find I have little alternative

So I will be chronicling some 'how to's' on making a TT into a GT2 from a drive perspective. I will also quantify the weight savings. Near as I can tell, it should be about 200 lbs... I will also be installing a Guard Limited Slip (50/80 I think). Look for more in the near future....

ca993twin

bob, bob, bob,

what can I say? You are an inspiration to all of us. Good luck. How was your weekend?

viperbob

Weekend was Great. Very few cars to play with. I did get the chance to dice it up with a 2004 GT3 Cup Car practicing for a race later in the day. They can really hold you up... Did you know that? When you get by them though, they disappear in the mirror...

KRA993tt

Bob,

Looking forward to hearing about the conversion.

I guess no matter how wide the front wheels are with the FWD it is going to make it push?

Jean

Bob,

We will be looking forward to your progress. I am planning for the same 2WD route and 200lbs weight savings.

What kind of RWHP do you currently have, I know you were targeting 600 FWHP, where do you stand today. Also, we haven't heard about your feedback with the newly modified K24 turbos, have they made a quantifiable difference in performance?

Thanks.
Jean

Kevin

Bob;

I'd take a different approach.. I'd be removing the amount of lockup or torque transfer in the tranny... How about removing 10-15% first.. before dumping the entire 4 wheel drive!

ScottMellor

Bob, and you seem so normal in person.

JJayB

Bob,
Last year I went through a similar problem. My rear tires had a diameter or .29mm larger than the fronts. Every "knowledgeable" source told me that shouldn't made a difference. Just add some more wing, stiffen the ft. and more camber. Then I remembered seeing a Canadian driver Jean-Francois Dumoulin go thrugh a field of Vetts and Vipers in his 993tt after a tire change. After the race he mentioned that the car was very sensitive to the tire set-up.

I abandoned the 315 and went to a 295 with a 235 ft. The understeer was gone.
I'd try a different tire set up to assure myself that's not the problem.
Scott Mellor has a new set of Pirelli's I'm sure he'd let you test for a few laps.

fc-racer

Viperbob,

I would not take out the AWD drivetrain unless you are doing it for weight/drag reasons. The AWD is superior on the track, wait until you go RWD only with the HP you have, the car will be almost undriveable and you'll constantly be tip-toeing out of corners.

I ran into the same problem with my racecar, 475hp being put through four skinny 225/45R17's! with a weight similar to our twinners. The solution for me was to use a limited slip in the front differential. This cured all of our power exit understeer. We were able to drive around the problem quite well by using more of a divebomb approach to corner entry, pivoting the car and then accelerating in almost a straight line. The sweepers were a bit more tough, but we still found that we were quicker through them, even with the car feeling awful.

The scariest ride ever was when we disconnected the front drivetrain and were running 475hp through the rear wheels! That was undriveable IMO. The only thing I dislike about AWD is that it can be a bit unpredictable at times, but the twin turbo seems to be very good in that area, whereas all other AWD systems I've raced seem to have a mind of its own.

viperbob

JJayB - The tire diameters in the front and rear are identicle 650mm. I was having the problem with the Hoosiers, and the Yokohamas. I am sure it is not the tires. Thanks though and yes they are sensitive here....

Jean - Around here unless I have dyno number to back it up I would rather not EVEN speculate... I hopefully will be taking it to the dyno very soon. The new turbos seem to be doing very well.....

Kevin - Instead of going to the trouble of trying to adjust torque split, I just plan to remove it. There is nothing that is permanent, so it could always be reinstalled in the future.... I will give you a call later today on some other business.....

fc-racer - Trying to deliver too much power through small tires IS a big problem. I am currently running 320 (actaully measure 335) on 12 inch rear wheels. My fronts right now are 265s. I am also trying to remove overall weight in the car. As I estimated, I should be able to knock off 200 lbs... I agree that the system in the TT is very good. It is just that I can not get a good balance with more power.

Scott - You just did not get to know the real me