YearOne

Has anyone installed the Cup car crown wheel and pinion in their GT3 to shorten the final drive?

MJSpeed

Search is your friend...

ring and pinion or R&P 4.0

Erik

Just did it last week. Top speeds in all gears much lower, top speed in 2nd is right around 64mph, top speed in 3rd is now right around 100mph which is/was the important one for me since most exits at our local tracks just seemed to have me on the rev limiter in second, but seemed to be too slow to take in 3rd. Car definitely feels faster, but I have not had the opportunity yet to take it to the track where I would really be able to tell the difference. Traqmate doesn't lie :-). Only negative so far seems highway at my cruising speed of about 80 mph is now at 4K rpm, which seems a little loud after 30 minutes. First gear is really short now, but I never made it to redline in first anyway. Will update in 2 weeks after my first track event with the R/P

triode

Erik, what was your all-in cost for this mod? Right now my car does 85 in 2nd and 115 in 3rd and I'm very interested in more usable max in-gear speeds.

Erik@GBox

Triode,

I would be happy to help you with this. We do this modification for quite a few road cars looking for some extra acceleration and more usable gearing.

Give me a call and I will be happy to discuss the costs involved with this process.

Happy to help,


Erik Johnson
GBox Performance Transaxles
(303) 440-8899 work
(303) 895-4828 cell
www.gboxweb.com

Erik

I was quoted about $3800.00 installed, the price of the R&P (Porsche Motorsports) was $2350 and 10 hours of labor. But while they were in they replaced a couple of items besides all my clutch and pressure plate items. My Pinion Shaft bearing also needed to be replaced and some other nuts and bolts "while we are in here".

996FLT6

1st gear useless. Top speed is 178 for the 6- don't know bout the 7. 3rd gear has very usable trq band but certain turns a stock gt3 where they are on 2nd and I'm on 3rd they can out accelerate me at exit ie t11 at thill. If u track alot changing gear ratios is the better option. Thee best mod I ever done is getting a guard diff(u get faster laptimes because u can brake alot later and exit faster). I would do that 1st before rp(if your LSD is gone). Mike

GTgears

One of the liabilities of installing the 8:32 ring and pinion is that it doesn't have a terribly long service life. Because the gears don't "hunt" they wear a lot faster than the stock 9:31 does. While it's a very popular modification for weekend racers to install in their street cars, Porsche never intended the 4.00 R/P set to last any longer than 1 service interval (+/-30 hours) on a race box. A street car that sees some track time will obviously get way more of a lifespan out of it than that, but it's still something to consider from a cost effectiveness perspective. Gearsets will cost a little bit more up front in parts' costs, will generally be less labor to install, and will last longer. Just something to think about.

Regards,

Matt

cfjan

Matt,

What's the main difference between the 8:32 and the 9:31 gearsets? (i.e., can you elaborate on what you meant by "hunt"?)

Thanks!!

mooty

right on.
ask how i know.

GTgears

The numbers are the toothcount of the pinion (small number) and the ring gear (large number). On the 8 tooth pinion it divides into 32 evenly, meaning the same tooth hits the same opposite tooth every single time it spins around.

The 9 tooth pinion takes a number of cycles before it hits the same tooth on the ring gear. This creates a variance to the wear patterns and tends to make the gear pairs last longer.

The other thing to think about is the fact that the 4.00 R/P set is spinning roughly 15% faster than the stock one is. What this means is that not only does it actually wear faster but it makes everything wear faster. Your gears all spin that same percentage faster. And as was mentioned above, when cruising down the highway, your engine spins that much faster to stay at 80mph while you travel on the interstate. While I won't attempt to estimate the amount of miles or hours that this accelerates the service interval on things, the reality is that it does speed these things up. For many guys that's a tradeoff they are willing to accept. For others it's not.

If the car is only tracked on shorter tracks then you can consider regearing it while leaving your stock 6th gear for highway use. But each case is different and what works for one guy won't be always be right for someone else.

996FLT6

So with respect to cupcars do they do the rp as well as changing gearsets Matt? If u have a rp and decide to do gearsets would the gears be ne different then some gt3 with a stock rp? What is the advantages/disadvantages of both at the track other then rp will wear it faster/shorter life. Thanks. Mike

996FLT6

And how much would it run : )? Thanks. Mike

GTgears

With Cup Cars it's often complicated by sticking with only homologated ratios. Depending on gear position, we generally make between 2 and 3 times as many ratios as are homologated. But the answer to the question is that they do change ratios while using the 8:32 ring and pinion. And because of how short it is, in some instances that means going with taller 5th and 6th gears than "stock".

With a Cup Car in a professional race setting they often have the leisure of being able to gear specifically for each individual track they race at. Most of us recreationalists don't have that luxury and build a more generalize box to fit whatever tracks are closest to us. In a situation where you may run 2 short tracks and 1 long track in your region, you may have to make compromises and favour one track over the other. That's one of the biggest challenges of being a privateer racer on a budget. You can't just rip it out every other weekend and make it perfect for where you're running today.

Guys who have been at this for a while who used to race 911SCs and other other cars with 901 or 915 gearboxes will probably be familiar with many of the more serious guys in their region having a pair of gearboxes that they swtich back and forth depending on venue. That was convenient, when we're talking about boxes that could be custom geared along with an LSD for less than $10,000 per box. But try that with a GT3. You're going to be into your spare gearbox for twice that or more. Definitely something that's not in everyone's budget. So instead we get stuck with building compromise gearboxes and relying on the wider powerband and better torque curves of the modern engines to make up for deficienies in gearing.

As for pricing? Shoot me an email if you want to talk more in detail. I'm not trying to be tongue in cheek here but I do try to respect the fact that I am not a paying vendor on this board. I post information here and engage in technical discussions, but don't want to be selling here.

P.J.S.

excellent input gt - thank you