i used to run this gearbox in my old gt2 racecar, to high geared but very strong. we used a 75/90 that 76 racing lubricants sell called sunoco gl 5 superlube. it stands up very well to heat and hours of abuse on track. dont know about any other oils for non road use anyway,but this stuff is great, i use it in my old gts race car as well. its 60 quid for 20 litres so you get a few fills of it

hope this helps

I changed mine to Redline synthetic gear oil, 75W-90NS, when I put the short shifter and 997 transmission mount in. Car is modified and had probably done around 35k at the time.

IIRC the recommended change interval is 90K miles. My tech buddies tell me the transmission/diffs are robust but I had my 03 Turbo's tranny/diff fluid changed at under 40K miles. Glad I did because in prepping for this job, removing panels to get at the tranny, he spotted a leaking seal around a selector shaft. I got a new transmission covered by the CPO warranty.

Just recently I had the tranny/diff fluid changed in this replacement tranny at around 90K miles so this means the replacement tranny/diff fluid had around 50K miles on it.

The techs tell me that if one wants to be a bit anal about tranny/diff fluid changes to cut the factory recommended fluid change interval from say 90K miles to 60K miles, 50K miles or even 45K miles.

The only way I'd change the fluid annually is if I tracked the car. A lot.

Sincerely,

Rockster.

Not to put too fine a point on it but with the selection of Shell Helix you have stepped off the reservation regarding Porsche approved tranny/diff fluids.

The problem is the Helix fluid may be incompatible with the transmission and its lubrication needs.

However, given that the engine has been tweaked to up its HP output there is no guarantee the Porsche approved fluids would have sufficed.

But with that much extra HP flowing through the transmission it may not matter that much.

The transmission because it has sufficient margin it can tolerate the higher output of the engine and because the Shell Helix transmission fluid does all the right things (and does none of the bad things) the transmission may be just fine.

Or the transmission doesn't have sufficient margin in which case the fluid choice may not matter that much.

No fluid is going to make an input shaft stronger, tougher.

BTW, remember the front diff can receive up to to 40% of the engine's torque so the front diff can receive more torque than its design was intended to handle.

If you believe Shell Helix will help the tranny/rear diff survive this added torque load you have to believe it can only help the front diff.

So, you might consider treating the front diff to a filling of Shell Helix fluid as well.

Sincerely,

Rockster.