boqueron

The car is loosing oil and my shop says its a crankshaft joint. I have to separate the gear box group from the rest. I wonder if it could it be the right opportunity ( with the gear box there ) to change the upper gear ratios (4,5,6 ) and shorten them a bit ? I mostly track and don't really need so "long" 5th and 6th gears... ( specially not the 6th which I never have the opportunity to use at the track ).

I want to keep the possibility of travelling with the car....

What would be your recommended gear ratio and - if possible - the Porsche reference for it ?


Thanks in advance ,

Larry Harris

I suggest you change 3, 4 and 5th gears leaving 6th alone. Thats how I'm doing mine. This would leave the factory 6th in the car for long range touring, and good fuel economy. Some others may say put the existing 5th in place of the existing 6th. Either way will work. BTW the gears are not cheap.
Good luck.

boqueron

Thanks Larry, it makes sense !

David A

use the one from a CUP car.It's all OEM too.

Cupcar

996 GT3 ratios are 3.82 > 2.15 > 1.56 > 1.21 > 1.00 > .85 and the ratio splits are .56 > .73 > .77 > .83 > .85

997 GT3 ratios are 3.82 > 2.26 > 1.64 > 1.29 > 1.06 > .92 and the ratio splits are .59 > .73 > .77 > .82 > .87

Keeping the original first and using the second from a 997 GT3 box, Motorsport sourced ratios in 3,4,5 and moving the direct 5th to 6th you could have:

3.82 > 2.26 > 1.684 > 1.364 > 1.174 > 1.00 splits would be .59 > .75 > .81 > .86 > .85


Rpm post shift
996 Stock > Modified
1>2= 4592 > 4838
2>3 = 5986 > 6150
3>4= 6314 > 6642
4>5 = 6806 > 7052
5>6 = 6970 for both

Cruising RPM would increase 15% and top speed would decrease 15% to around 162 so this would probably not be a change for a daily driver.

boqueron

Cupcar, THATS a detailed information !! Thanks !

Cupcar

If interested the Porsche Motorsport part numbers for gears 3,4 and 5 above are:

1.684 = 996.302.953.9B
1.364 = 996.302.954.9F
1.174 = 996.302.955.9C

The 2.26 second gear ratio would have to come from a 997 parts list which should be available in Europe.

NJ-GT

The 997 GT3 runs on 1.3" taller tires and uses the same 3.44:1 R&P, so the shorter gears aren't helping that much.

2nd gear can't be changed on the street 996 GT3. 1st and 2nd are fixed. With the GT3 Cup transmission, only first gear is fixed.

The most common upgrade, is to get new 3rd, 4th, 5th, and reuse the stock 5th into 6th. The stock 2nd gear is ok for the track, I never had a track day where I needed to downshift to 1st when running the stock gears/R&P.

I use a shorter RSR R&P 4.00:1 with stock gears. The spacing from 3rd to 6th gear is pretty good, but you don't get to use the last two gears at the track with the 3.44:1 stock R&P. My top speed in 6th gear is about the same than the stock 5th with stock R&P, my second gear is short enough to have fun in Solo Racing.

NJ-GT

By the way,

These are the gears I would choose if re-gearing 3rd to 6th using the stock R&P and 295/30R18 MPSC.

Gear Ratio --- Gear --- RPM drop on upshift --- Max Speed
===================================
2.15----------2nd (stock)----------5600rpm----------83mph
1.684----------3rd (new)----------6400rpm----------106mph
1.409----------4th (new)----------6850rpm----------127mph
1.174----------5th (new)----------6850rpm----------149mph
1.00--------6th (stock 5th)--------6850rpm----------174mph

a shorter 2nd will hurt the upshift to third at the track.

Cupcar

Good point on the racing mainshaft having a separately changable gear in the second position and only the first gear machined onto it. The street mainshaft has BOTH first and second machined onto it. I should have pointed it out.

The street 997 GT3's mainshaft would replace both first and second gears to the same 3.82 first as the 996 and the lower 2.26 ratio for second.

There are no lower second gear ratios than the 2.15 available from the Motorsport department and the only ratios available for first gear with the racing mainshaft that allows individual replacement of second gear are: 3.15, 2.54 and 2.33, not the stock 3.82.

NJ-Gt's solution would be a lot cheaper but have the stock 996 GT3's gap from first to second with nice progression after that and would be a better box for track use. Driving in town, the lower second of the 997 would be nice...compromises, compromises.....what makes it interesting.

boqueron

NJ-GT , thanks for your advise. Could you please explain the meaning of R&P ( my english ...!)

boqueron

Cupcar, NJ-GT

would you know, by any chance, the part number of the 1.409 gear ratio ?

Cupcar

1.409 = 996.302.954.9E

NJ-GT means "Ring and Pinion Gear" when he uses "R&P". The racing Cup 996 uses an 8:32 "R&P" gear = 4:1, part number 996.302.911.80 if you want to add this to your list of potential changes.

Bob Rouleau

Harry - the Ring and Pinion gear is the final gear in the differential.

A higher number on the R and P will make all the gears in the box shorter.

In other words a 4:1 rear end ratio (that's determined by the R and P gear) will make the engine hit the red line at lower speeds in each of the existing gears. Changing the R and P is cheaper than changing individual cogs in the gearbox (they cost a lot!) and has the effect of providing quicker acceleration in each gear at the expense of lower top speeds in each gear.

best,

Cupcar

The stock street ratio is 31:9 = 3.44:1, so a change to a racing 8:32 moves it to 4:1 which means the car will be going 14% slower in each gear at any given RPM.