I am curious what it takes to make the 901 as good/better than the 915.

A good 915 will cost $ X, but to upgrade the 901 with the aluminum side plate, intermediate plate, stronger 1st gear etc will cost just as much right?

I don't think it is possible to make a 901 surpass the strength of a 915. The 915 is an entirely new design to improve upon the 901's short comings. Sure, you can upgrade a 901 and make it better...but it is wishful thinking to believe you can make a 901 "even Steven" with a 915. On an up note, I know a guy (Randy Beck) who is a masterful racecar driver who raced a 3.2 300+HP motor mated to a 901 and never blew it up. It has alot to do with how smooth and intuitive you are. If you are a Conan the Barbarian kind of guy...a 901 will not last long behing big HP. My two cents.

how much hp you planning?
What kind of driving?

We'll tell you how much $$ to bring..

210-230 hp

Auto - x, driving schools and open track days for fun.

stronger 1st gear??

there is no such modification that I know of.....it would require a redesign of the end housing..in the picture, item 4 is 1st gear, to make it more robust, you'd have to hold it in place from both sides. Then you'll be limited by the diameter of the shaft.

Click to view attachment

as for the aluminum side plate, not sure if that is really a problem part or not....


the 901 transmission is perfectly designed for it's original application, when HP/torque started to go way up, Porsche did a clean-sheet redesign for a reason, you didn't see them band-aid the 901's

And, despite the "clean sheet redesign", 915s have a nasty habit of scattering second gear. Of all the 915s I've rebuilt, most came apart for that. All had loose bearings in the differential housing part of the case, too. The Cap'n

How much torque? That's really more important. A low-torque 200hp engine will allow a 901 to live just fine. You can get 200hp out of a 2.0 Six but it doesn't make any more torque than the 2.0T that came in the 914/6 to begin with.

I never said they are perfect

Looking for 220-230 lb/ft of torque....before my 600 shot of nitrous...

I love it when people on other forums spout off ridiculous stuff like that...don't you?

The cost can be pretty painful if you are going the race route which it sounds like you are. A limited slip and it's installation can add about $1500 or so to the cost. A set of lower gears such as M-S-X, new bearings, sliders, dogs or whatever else is in there that wears can add well over a thousand and then having a good transmission person set it all up is a big cost. To make it shift you'll need one of James' Rennshift shifters and an aircraft coupler to get rid of the sloppy coupler and finally a Terry cable and one of Patrick's high temp cable wheels on the case. Since the trans will be used on track, a lube and cooling system should be considered to make the R&P and gear cluster live longer and the nozzles can easily be installed when the trans is apart. When I did all this to mine I finally ended up spending about $4,000 total including labor but it sure has held up well and shifts like a dream. I already had the lower gears so that saved a big chunk of $$$.

What company makes/sells the best quality gearsets?

I want to say your only choice is factory gears from used boxes...

powerhaus makes or imports new gears

How much truth is in the statement that the factory gears (metallurgy) is pretty brittle which is why they break?

I've never heard that....


The reason they break is that they were NOT DESIGNED for 300hp/trq which is what people can and have pushed thru them...there are higher HP cars with big V8s being run behind 901 boxes...if and when they fail, it has nothing to do with the failure of the box, but the owner trying to ask more out of a 75 pound gear box that was used behind a 100hp motor...

supposedly it is the case that starts to fail at high power abuse, it has a hard time holding the gear sets in line with each other....the billet intermediate plate only holds one end of the gear stack (see picture I posted above)

the 901 based boxes (as used in the 914) have a magnesium case, the later year cars used aluminum.

Why not look at using a later model tranny. The syncros in the 915 aren't all that much better than the 901. Maybe look at using the Gearbox from a Boxster. There are several different itterations out there that you could get gears from. You may have a tougher time finding a limited slip though.

I agree with mike.

I have had 350 tq (a dyno'ed 315 tq before a rather nice fuel injection system which REALLY puts the power down...) run through my gearbox for months, and it handles it fine! I know my box is sloppy too... I have a rennshifter, new bushings, and the gearbox is sloppy as hell... but it handles the power! I have 2 spares and a 915 ready...


Dont ask how many cv joints i've broken...

230tq will be fine with a 901. First gear is about limited to 160tq... so dont nail first.

Andrew

ps... I drive it hard... 40ft black lines are this cars specialty's (ps.. no clutch dumping.. hehe)

I agree. Although I have mail from Guard Transmission that says they plan to offer 901/914 gear sets later this year. Quote: "We don't presently carry 914/901 gears, but late this year we probably will." So keep your fingers crossed, we need a source.

I run about 300 HP through my 914 box and plan on a rebuild every second season. I lost the R&P at Thunderhill in May. Here is the replacement ready to go in.

Nother pic:

As I have mentioned before and Herb Meeder has verified, I have a "built" trans with racing gears M-S-X for the top three, Quaiff limited slip and has two race sessions on it. I will sell it for $3500 plus whatever shipping is to where ever anyone lives. While this seems like a lot of $$$, in reality it is cheaper in the long run.