901 trans - when are upgrades needed?

[uglydog56]

I just bought a 68 that I'm going to use for backroads hooliganism and occasionally attempt to autocross in. I have the irs arms and Porsche brakes for the back already. I have a 914 rear shift (back shift? not side-shift) that is in decent shape. I've found a good running 1.7 bus type iv that I'd like to just put a mild cam in (a scat c35 probably) and toss it in, doing a cali conversion for cooling.

My question is: I'm looking at maybe 80hp here. It'll be a long time before a put a 125-150hp engine in there. At what point do you need to change the intermediate plate or do any internal upgrades? It is easy to spend a lot of money in a hurry on a 901. If it's necessary, I'll do it now. But if not, I'd like to wait a few years down the road, when I upgrade the engine.

[Piledriver]

Porsche considered a 901 trans rated to be good to ~250 lb/ft of torque.
An aluminum $$$billet carrier plate extends that to 350-ish.

You can spend silly money on a T1 or bus trans and really never get the power handling capability.
If you were going to road race it, a trans pump/cooler setup would be a good idea, Porsche used one on their 914 racers back in the day. At least you can get a good AND cheap electric pump for that use these days.

Rebuilding them even bone stock is pricey, but if it works OK, you should be just fine with a NA motor---even a badass one- forever.

The Porsche synchros sort of suck for fast shifts, even when new.
You need to adapt your style to them, as they are what they are.

Just note that 1st gear was an add-on to the original 4 speed design, 5th lives in the nose cone and is only supported on one end... so 7000 RPM clutch drops for a hard drag launch are very strongly discouraged.
The guys with V8s frequently get 1st removed.

[uglydog56]

Sounds like I should be okay with the stock plate then. I'm going to leave 1st gear installed and just be a good boy. My plan is to disassemble in order to flip the ring gear, do an inspection, and replace anything bad, but only anything bad. This ought to keep the cost at $$$ instead of $$$$$.

[Piledriver]

FWIW the 901 can take a 228mm vanagon/late bay bus flywheel, just needs a pilot bearing installed cali-style.
Nothing wrong with the forged 914 FW or pressure plate, other than expensive to replace.
The stock PP/disc is good for 160+ lb/ft tq, probably more.
Kennedy can rebuild it stiffer for far less than new.

IIRC Wally had his forged 215 opened up to 228mm and modded for a floater, dual disc setup with a stockish pressure plate on his 2.2L monster. He ran a Porsche 915 trans due to the HP/TQ of the turbo motor.

[uglydog56]

the bus 1.7 comes with a flywheel, but I think it might be a 210? A 215 clutch disc wouldn't fit inside it, but the seller's clutch disc was not in the best of shape, either. I have the 914 flywheel/clutch as well. I'll probably use the 914 stuff just to keep it simple.