P.J.S.

I think gearing will make a 3.8rs faster than a 4.0

(flame suit on)

GTgears

Since nobody has said why the regear is better, only that it is, I will explain.

Taking a 2007/8 GT3 as an example...
2nd to 3rd shift has you entering 3rd gear around 6000rpm
3rd to 4th shift has you entering 4th gear around 6500rpm
4th to 5th shift has you entering 5th gear around 7000rpm

That's if you shift at 8400 rpm. If you shift lower, your rpms will be accordingly lower.

Peak torque is around 6300. To optimize acceleration, you want to keep your engine at or above peak torque. Changing the final drive does not change your rpm drops at all. You can only change that if you bring your gear ratios closer together. 3-4 is ok and 4-5 is pretty good. 2-3 is too wide.

They improved those gaps on the 997 chassis. If someone owns a 996, the gaps are bigger and the 3-4 shift does fall below peak torque. Porsche has improved the gearing over time, but there is still room for improvement there.

Also, my math puts a 4.125 ring and pinion with stock gears and a 26.4" (315/30/19) tire at just a tick shy of 174mph@8400rpm.

ps. TRG has recently been using our r/ps and gears in their Grand Am Cups that still have the Holinger box in them. It is part of why I am out of stock of 4.0s...

On Pole

Look what I found on my hard drive;

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

1.684 = 996.302.953.9B
1.409 = 996.302.954.9E
1.364 = 996.302.954.9F
1.174 = 996.302.955.9C


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


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.
8:32 "R&P" gear = 4:1, part number 996.302.911.80

Stock GT3:
gear ratio mph@rpm
1 3.82 45@8200
2 2.15 80@8200
3 1.56 110@8200
4 1.21 142@8200
5 1.00 167@8000
6 0.85 190@7700

GT3 Cup:
gear ratio mph@rpm
1 3.15 46@8000
2 2.00 72@8000
3 1.56 92@8000
4 1.31 110@8000
5 1.09 132@8000
6 0.91 158@8000

GTgears

As an aside, those of you guys who have regeared your 997 chassis cars should start selling your takeout 3,4,5 gears to your 996 chassis owning buddies. For 996 GT3 owners on a tight budget but due for a gearbox service, it's a pretty cheap way to improve performance and it lets you 997 guys get rid of those stock gears sitting in a box in your garage gathering dust. They'll also fit in and improve a 993 gearbox in a huge way...

cwhota

Thanks everybody for your input, i appreciate, As it stands now, i bought a complete very low milage stock GT3 transmission minus the case. I will use those internal for now and regear in the near future. I will call Matt tomorrow to finish the discussion we had today

Now back to assembling ;o)

Yes it did but that is what broke ( exploded would be more accurate) and brought a bunch of other stuff with it !!! So that is why is decided to take Francois internal tranny since he installed a cup Tranny
Put the diff apart and it is good.

FFaust

And he told me that "if I ever need a kidney"...

cwhota

What would the best combination since i'm back with the 3.44 996 GT3 ? to go in that sweet spot shift zone?

The On Pole sugestion is this and i heard something like that from others also
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

Darkstar1

Once Bill Rader installs my lower GT Gears, my stock 997.1 4 and 5 gears will be available...

Yes it is an old thread but I was researching and thought it was appropriate to bring up.

Thanks
Randy

rbahr

Hi All,

I missed this thread the 1st time around, but as my tranny is apart and on my bench again, and the 'while I'm in there' bug got me (again), I decided to make a few changes including the cup 4th, 5th, and 6th gears. I had already done the TT mainshaft (1st & 2nd gears). So I have the following ratios:

1st gear: 3.82 996 TT
2nd gear: 2.05 996 TT
3rd gear: 1.56 996 GT3
4th Gear: 1.308 Cup
5th Gear: 1.094 Cup
6th Gear: .912 Cup
R&P stock

The spreadsheet for the following should be attached.

AudiOn19s

stock 3rd with the stock R&P is an issue if you ask me. 3rd needs to be quite a bit shorter and closer to where 2nd currently is to get the most gains out of a gearing change as it's the gear you're in most of the time.

rbahr

I agree it's not perfect, changing the R&P would help...

Nickmysta

Please see my thread on the brand new OEM 3.89 R&P for sale

https://rennlist.com/forums/997-gt2-...9-r-and-p.html

GTgears

Doesn’t matter. You still lose power on the rpm drops.

cgfen

oooohhhhhhh

good thread.