Bill Verburg

other gear sets that could be used

Jim Richards

Thanks Bill.

quiquedb

hi Porsche race men, here other spanish fool about my 964 CUP specifications.

Matt proposed me the following combination

gearbox G50/03 from a 1990 964 Porsche

7000rpm
645mm diameter whell
18" rims

ring & pinion 9/31

1st gear 13/41 for 76,315 km/h 3,154
2nd gear 16/32 for 120,344 km/h 2
3rd gear 20/29 for 165,991 km/h 1,45
4th gear 23/26 for 212,916 km/h 1,13
5th gear 34/32 for 255,730 km/h 0,941

The car is just for race, no motorways, the longest straight we have in Spain is at Alcañiz circuit, 1.300 meters, almost other circuits have no more 950 meters... once we go to Spa Francorchamps to the Porsche days, and also we can race at Estoril (985 meters) or Portimao (969 meters) in Portugal

We expected when the car will be finished no less than 340cv and obviously we have LSD.

Need to give to Bill thousands of thanks about the brakes and his patient with me and my inexperience...

Also thanks to Matt and his patient too, need to talk about my gears...

My thoughts about the gear chart Matt propose me... I think need less gap between 2nd, 3rd, 4th and 5th, he talked about the rpm drops, but I can not find the gaps in his chart, I think I need less speed at 2nd, 3rd, 4th, but the best thing is talk about it and here I think is the best place for it.

Sorry about me english guys, is better than your spanish, but similar...

Thanks

I enclosed a photo for my car

christallon

Hi quiquedb,

Very nice car. Sorry for the OT, but what spring rates are you running up front?

Also, this is an awesome thread. Thanks to Bill and the other contributors. Outstanding detail and logic here

KaiB

Here's a tip, as I just went through the process of selecting gears for a G50.

Google (Porsche G50 gear charts) or simply G50 Gear charts or the like. You'll find several to download and work to your heart's content. Inputs are car/i.e. wheel specific and most of them are very good.

You'll probably want to gear fifth to the higest speed you hope to realize at the longest straight you frequent (or the one you'd like to be most competetive on). If you have much room for driving improvement, say in the next two years or so, you'll want to take that into account. It would be a shame to gear for today's skills (given the money it takes), only to realize that you're short by several hundred yards two years later.

Good luck.

Bill Verburg

here is you transmission w/ drops


3 things
I don't like non hunting gears like the second here

for a pure race transmission the top speed is pretty tall unless you are at tracks w/ real long straights, for most pure race transmissions a top of 140 -150mph is going to be fine, if it's a dual use trans then this is a very nice box

I really like the tall 1

sergiDA

Quique I think that Matt's proposal is as good as it gets if you want to keep 255 km/h and you are staying with 5 gears ... You are getting a 42/47 km/h drop between gears and less than that won't be posible.

sergiDA

Hi Bill:

What does it mean ”I don't like non hunting gears like the second here”, sorry by Spaniards can't understand that expression...

Bill Verburg

the 16:32 always has the same teeth meshing which promotes wear, if the ratios are other than integer #s then different teeth mesh on each turn(the gears hunt)

8:32 is the same sort of non hunting gear set

16:31 hunt, 16:32 do not

quiquedb

Yes, good question and amazing answer... I am riding standar JIC CROSS suspension!!! and the result for us (in Spain don't know that kind suspension are) is amazing. Standard rates of springs, here I don't have the rates, but may be some one can write it... may be 7kg/mm front, 9kg/mm rear???? I can't remember...

My mechanic said when he saw the JIC suspension that the look were pretty good, I have also a Bilstein for 964 RSR but he insist to install the JIC ones... and I need to say that the results were fantastic... but I need to prove in a real race during 2 hours...

quiquedb

Then??? you propose to change 2nd to a 16/31 gear ratio??? and the 3rd??

Thanks Bill.

I am agree with Sergi and Bill than the top speed is to much high... no more than 245km/h...

I friend of us bought to Matt the following chart for a real 964 RS NG-T

also mounts 18" rims, 645 mm diameter

6800 rpm
Real G50 Rs gearbox

1st gear 13/41 3,1538 for 75,399km/h
2nd gear 17/35 2,0588 for 115,501 km/h
3rd gear 20/30 1,5 for 158,530 km/h
4th gear 23/27 1,1739 for 202,566km/h
5th gear 30/29 0,9667 for 245,995km/h

I want to keep my 1st gear, what happen with this gear chart put in may car???

I forgot to say the weigth of my car: 1.066kg with out me

Thanks

Bill Verburg

here's the g50/10 that was used in the normal 964RS


here's the g50/52 that you listed for the NGT, this is a very nice track transmission

GTgears

I've just got a couple of comments to add to the discussion.

The first is that we've never seen any noticeable or significant issue on matched ratio gearsets and their wear patterns in the same way that we have with the 8:32 r/p set. Logic may suggest that there could be an issue, but our experience doesn't match up with that. And to support that, I will point to Porsche themselves and the fact that the 2.00 2nd gear ratio has been used as far back as Bill's 993 Cup Cup gearbox all the way through the 996 and 997 Cup Cars. It's a standard ratio that's installed in the gearbox from the factory unless otherwise specified. If it was a problem, Porsche would change it.

The other thing to consider in looking at the strength and durability of a gear is the actual toothcount. Porsche gets their 2.00 2nd with a 20:40 toothcount. We get ours with a 16:32. Below is a picture of a stock GT3 Cup 3rd gear next to ours.

The Cup gear is a 25:39 toothcount, which is 1.56. Our gear is 20:31, which is 1.55. Nominally they are close enough that they are interchangeable. But our gear is significantly stronger than the OEM piece, and not just because theirs is cast and ours is billet. You can see how much bigger the individual teeth and the root of the gear are.

We actually have an engineering program in place that lets us calculate the strongest toothcount for any given ratio. As you reduce the number of teeth, not only does the width of the tooth get bigger, but simultaneously as the teeth roll across each other, the amount of load transferred to a single tooth goes up. There's a balance point there where if you go with too few teeth, the individual tooth takes too much load and doesn't share enough of the force with the surrounding teeth. Our gears and toothcounts are optimized for strength.

I mention this, because for some of the above ratios that are being discussed, we can supply the decimal ratio being looked at, but will not have it exactly to the 1000th place. The Porsche 5th in Enrique's most recent chart is a 0.967. Our option is 0.960 with a 25:24 toothcount. You may want to consult our website for exact ratios as you look at this, just so it's 100% accurate.

Lastly, none of the charts I've sent to you guys are locked. If you want to play with other ratios and manipulate the stacks, please have at it. You aren't going to hurt my feelings if you want to mix things up and change things.

For example, on Sergi's chart, I picked the 3rd gear I did because when he's not at the track, it's going to offer marginally quicker acceleration from 70 to 150kph when he's on a public road bombing through a curvey canyon. If you want to emphasize the racetrack more with the stack and use the 1.474 Bill suggested, I would also probably change the 4th out to a 1.16 (25:29) 4th gear. It makes the box less dual purpose and more motorsports oriented.

Bill Verburg

Good points Matt, they used a 26:26 as far back as the '76 915 4th gear

I have made no effort to be sure that any of the speced gears are actually available, mostly I chart stock gearboxes where factory parts are used.

I believe that the problem gear in my /30 is the 38:25 3rd, at least that is the one that had to be replaced, it is also the one I use the most.

8:32 is the ultimate example of non hunting wear, because of the low tooth count(8) and high torque loads going through it and the extended time that the load is going through it. All conspire against long life

GTgears

3rd is usually the first to die, for the very reason you mention, it's used the most. Holds true for the 915, holds true for 5 spd G50 and all of the 6spds even. We sell more 3rds than anything else.

And it's that same sort of reason that I don't think we see many problems with 2.00 2nds or 1.00 5ths. On the 8:32 R/P it's always running no matter what gear you are in. While all gearsets are meshed at all times, unless you are actually engaged in 2nd gear and putting the load on it, it's not seeing significant wear. So while the R/P sees 100% of the usage, 1st probably sees 10%, 2nd 15%, 3rd 30% (or more), 4th 25%, and 5th 20%. (Numbers are arbitrary guestimates, so if someone has telemetry that significantly disagrees with my numbers, I will not be surprised)