Too Short & Too Wide

[racerone]

I purchased a 2004 GT3 in late October. FANTASTIC car! I installed one of Europipe's excellent exhaust system as well as a BMC filter recently-----for those interested, I consider the pair as very worthwhile additions more than meeting expectations. Perfection is in the eyes of the beholder. As near to the latter as this car is I wish I could change the bottom ratio to one approximately 10-15% taller. The yen is the car's ability to poodle about at walking speed, the yang is unless one has grown to have the shifting reflex of a Roy Jones counterpunch say hello to the rev limiter. With the variable cam timing the motor is easily capable of launching with a slightly taller first gear. My questions: a. How difficult to change first's ratio; b. Is this beaucoup in parts and labor; and c. Am I alone in this impression? When driving on city streets at essentially legal speed it seems every time time I have approached a certain flat ingress ramp to a parkway, as soon as modest power is applied the car simply has a mind of its own about pushing hard to the outer lane. My suspicion is this is part of the limited slip rearing its race-bred pedigree at a less than opportune moment. nevertheless, this is SOME push! My query is: a. Perhaps the slippage has not been fully broken in as the car has but 1400 miles; b. The car is so rigid and the rear tires so well planted, especially under modest power, this characteristic falls under the nature of the design; and c. Of course, anyone else notice this?

[Tool Pants]

I do no know the GT3 and was tempted to say contact Porsche Motorsports as for the 996 you cannot buy any internal transmission parts. But on the GT3 they do list transmission gears. But there is only one 1st 2nd gear set listed so it must be the one you already have. Hope someone can be of more help. Jeff

[mds]

Kind of a unusual request, IMO, feeding in throttle in a little slower will accomplish the same thing won't it? But yes taller mainshafts are available. I think they run roughly $2k parts and $1.5k install. And the push, well it sounds like the driver again not the car. No offense intended, I don't mean to be rude, but how about some high performance driver training?

[clord]

Check out the thread I started in September on this board entitled "GT3 Steering Precision". There is a noticeable on-off throttle effect. It appears that all GT3s have it and I am concluding that it is an artifact of the performance-serious suspension set up. The GT3 has a lot fewer rubber bushings in the suspension joints that can otherwise 'auto-correct' for on-off throttle effects. I don't think that the effect I describe is due to the LSD as it would induce the opposite effects if it were the cause.

[JimB]

racerone,

If you were to describe in more detail the situation you are in when your GT3 starts to push we could probably diagnose it for you. LSD will induce push but it would have to be under pretty hard acceleration. Enough that the LSD would be engaged. I really doubt that it has anything to do with the lack of rubber bushings. I would say the most likely cause is that under acceleration your rear is compressing while your front is lifting causing the front to loose traction and push a bit. In a car with adjustable shocks you would take a little rebound out of the front or reduce compression in the rear and try it again. On your car you might be left to be a little more gentle with the throttle in the early part of the corner.

As I said, if you describe in detail the situation we might be able to provide more help.

Jim

[racerone]

Gentlemen,

Thank you all for your considered responces to my posting. I had the opportunity to speak with someone at PMNA who opined the source was probably the limited slip, adding further it should diminish with a bit more time and mileage. To reply to JimB's posting: The push is on a flat 40mph right-hander under no more than 75% throttle in second gear. When backing off the GT3 comes right back.....nevertheless, this would be spooky with something hard on the leftside or in the wet. All cats have claws (most anyway!), you have to learn more of their nature. I plead "no contest" at this time as this is the first Porsche I've owned since 1975 (911E-1971).

In my opinion JimB has it sussed, as the rear squats and the weight transfers to the rear the car simply pushes without taking some step(s) to mitigate this act of vehicle dynamics-----as there is provision for adjustment, balance can be restored. The place to find this is, of course, in a controlled enviroment (IE: racetrack).

[mds]

A common cause of understeer is an entry speed which is too slow for the corner followed by acceleration before the apex. This type of driving can also lead to oversteer in wet conditions since the steering wheel is not being unwound sufficiently as throttle is added.

So consider your driving technique first. Then try adding negative camber to the front tires and softening the front sway bar.