Maximum power through a G50 gearbox

Willem Fick · 03-07-2013, 03:13 AM

Hi Folks,

Does anybody here have a view as to what the maximum power and torque is that a G50 gearbox can reliably deal with? The particular gearbox I am looking at has part number 950.301.102 3R. I intend to use it in an application that will transmit around 420ft-lbs and 400hp.

Warm regards,

Willem Fick

twistoffat · 03-07-2013, 05:27 AM

The G50/52 gear box from the later 964 could take 360HP and I can imagine some tuner taking it to 400HP. Each new version of the G50 was improved on from the 1987 whaich in 88 got a new fork etc.

Tippy · 05:37 AM

More than you can throw at it.

I've heard of a couple folks running over 1000 whp in theirs drag racing.

I've had around 500 ft/lbs for many years in a G50/01 without issue. The 00/01/02's are the weakest series that require a billet diff cover for reliability in extreme conditions. Mines still original cast cover and hasn't had an issue.

Matt Monson · 03-07-2013, 05:57 AM

Willem, you have nothing to worry about at that power level.

Regards

Matt
Guard Transmission llc

hcoles · 03-07-2013, 06:38 AM

Then why do the V8 conversion people mention Turbo gearboxes with special modifications?

Tippy · 03-07-2013, 07:15 AM

G50/50 or /52 is a turbo gearbox.

spuggy · 03-07-2013, 07:28 AM

Quote:

Originally Posted by hcoles

Then why do the V8 conversion people mention Turbo gearboxes with special modifications?

V8's don't (usually) rev high & can make immense torque at low RPM - using a turbo box means you get the tall CWP (saving $3000 over buying - e.g. - an Albins one), which suits the motor characteristics much better...

Matt Monson · 03-07-2013, 07:38 AM

Quote:

Originally Posted by spuggy

V8's don't (usually) rev high & can make immense torque at low RPM - using a turbo box means you get the tall CWP (saving $3000 over buying - e.g. - an Albins one), which suits the motor characteristics much better...

Actually, almost all the 5spd G50s, whether turbo or NA all run a 3.44 final drive. The difference comes in the gearing.

A G50-01 has a 0.89 5th gear which provides for a 170mph top speed and roughly 3000 rpm at 75mph on a 25" tire.

The G50-50 on the other hand runs a 0.76 5th gear, which gives you a 200mph top speed and drops 75mph cruising to around 2600, which for an LS7 or other V8 is a much nicer cruising rpm.

The ONLY strength difference between the turbo and NA boxes is the ring and pinion. Gearsets are all the same thickness and same strength across the line. In fact, the gearsets are virtually unchanged from 1989 to modern 997 turbos and GT3s. All the later gearboxes got the bigger 9" ring gear, but the gearsets themselves are pretty much the same and with minor tweaks are cross compatible across all the G50 and G96 family of gearboxes (except 996 Carreras which have an oddball gearbox that still carries the G96 designation).

Matt Monson · 03-07-2013, 07:42 AM

Quote:

Originally Posted by hcoles

Then why do the V8 conversion people mention Turbo gearboxes with special modifications?

The other thing about the "modifications" is that many of them are being put into midengine kits cars like the FF GTM Mulsanne or the Ultima. For midengine, the gearbox needs to be inverted to run the other way around. It requires moving the drain and vent to the opposite side of the gearbox. Also, if the gearbox has a pump and internal oiling it also requires moving the pickup of the pump to the opposite side as well.

The other modification is a billet side cover, which even on the turbo and other 9" ring gear boxes is nice to have. You don't know how many GT3 gearboxes I have seen where the stock side cover allows enough ring gear deflection that the bolts on the back of the ring gear hit the cover when things are hot. The stock cast covers have a lot of flex to them, and doubly so when you go from 300ft/lb to 500 or 600.

Tippy · 07:57 AM

So Matt, if you have a billet diff cover on a G50/00, 01, or 02, will they be as strong as a 50 or 52?

Can't decipher if you're saying the diff's are the same (physical size of ring/pinion) or not between the NA/turbo G50 boxes (so all you need is the billet diff cover to match strength of turbo G50's?).

TIA

Matt Monson · 03-07-2013, 08:33 AM

The diffs are the same, but the actual size of the ring gear is not. The NA ring gear is 7.5" and the turbo ring gear is 9". On either of them I would add a billet side cover if going over 400.

Tippy · 03-07-2013, 08:56 AM

Thanks

Iciclehead · 03-07-2013, 10:10 AM

Can you switch out the side cover without doing a lot of work or does it require resetting the ring/pinion?

Thinking of putting in a reinforced side cover and wondering if it is (hopefully) a bolt off/bolt on installation.

Dennis

Matt Monson · 03-07-2013, 11:57 AM

It does require checking and potentially resetting backlash and bearing preload.

Tippy · 03-07-2013, 12:27 PM

You can do a depth check dimensionally and if the billet matches factory cast, should be ok, correct?

Matt Monson · 03-07-2013, 01:08 PM

You can but I still consider that taking your chances. The adjustment shims vary by 0.05 mm increments. That's not a lot of wiggle room for mistakes in measurement. The factory tools will offer the most accurate measurements.

Tippy · 03-07-2013, 03:12 PM

Ok, will look into.

Don Nguyen · 03-07-2013, 09:31 PM

How do you know what kind of G50 gearbox you have? I have a 92 964 C4.

Willem Fick · 03-07-2013, 11:13 PM

Thanks for all the great info guys!

Matt Monson · 03-08-2013, 08:58 AM

Quote:

Originally Posted by Don Nguyen

How do you know what kind of G50 gearbox you have? I have a 92 964 C4.

Most likely a G64-00. The 4WD cars got slightly shorter 2nd and 3rd gear ratios than the 2WD cars, but 1st, 4th, 5th and the final drive ratio are all the same.