I am going to be making about 180HP out my little 1974 914 and have heard the original 901 is good to about 200. The problem is, is that the 901 tranny doesn't seem to be made for fast shifts or even power shifts. Can the 901 be improved, or would it be better just to go to a different tranny. If so, which one? (without breaking the bank too heavily)

The 914 trans wil be fine. No, its not a speed shifter but with new bushings and proper adjustments you can get it pretty good. There are a few guys who have made cable shifters with some real good results. I am running 425 HP through mine, no problems for 7 years now.
Anything else is big $$$

Mark

"Power shifts" are a REALLY bad idea in any transmission with "Porsche style" synchros. Finesse is the way to get extended life out of one. You want a drag car, buy one. Leave most sports cars to the superior handling crowd ................

The Cap'n, who busted a few early VW and Porsche trannies in his youth.

The 915 is an option if you want better shifting and more strength, but you will pay a weight penalty.

If you want a lightweight transmission for a mid-engine car making that kind of power you probably want a hewland. You can get ones that are lighter, can handle more power, and some of them even have features like sequential shift and inboard brakes.

180hp won't break a 914 (901), but it will depend upon the torque. And likely to go before the transmission will be the CV's. There are good solutions to the CV problem posted on this site.

A Porsche mechanic (and big time racer/builder) says a 914 (901) will work OK up to 250HP.

I am pretty much hell bent on getting a Boxster S transmission in my car this coming winter. 3 grand for the transmission rebuilt, figure 1-2 grand for clutch and other parts and shifter. maybe 2-3 grand for the work involved to get it to work.

No more shifting problem since you got a new boxster shifter. Quicker smoother shifting.

As Brad on the 914club points out you have to figure out a way to put on the starter. Some machine work on the bell housing should solve that. Of course I really don't know exactly how it's done. But that seems to be it.

I still run a 901 on my car, so far so good.
I don't use 1st gear anymore. I've got enough torque to just take off in second.

That said, i do have a spare 915 with flipped R/P collecting dust. Just in case ...
Andy

HP is not the issue with 901's, it's torque. Both constant and "peak" or shock loaded torque.

There's a few options for linkage, but the first and easiest is to freshen all rubber and plastic between your shifter and your tranny. (mine is really a nice shifting car and it's stock)


Marks914, out of curiosity, is your 425HP more than 350 ft lbs torque?

Some rule of thumbs for transmissions:
- Up to 200 HP for street/auto-x use will be fine but no speed shifting as noted.
- Up to 200 HP for wheel to wheel racing with a pump/lube system and open it yearly to do bearings.
- Up to 250/260 HP for wheel to wheel with a pump and lube system and open it every couple of races to do bearings. Also use the stronger intermediate plate and the stronger side plate to reduce the flex on the ring and pinion.
- Over 260HP use a 915 for wheel to wheel and open it yearly for bearings and also run a pump and cooler system.

In all cases put in new linkage bushings yearly, use a high quality shifter like the Rennshift and replace the center coupling with an aircraft unit. If you convert the rear axles and use heavier axles and CV joints then something else will fail so what we do is use the stock axles and those nice modified type 1 CV joints and have a complete spare ready to bolt in when one fails. So far I have never had a transmission fail and I run a pump and cooler system and it takes 4 quarts of Swepco which helps a lot.

Additionally we use a spring center racing clutch to reduce the shock load on the input shaft and it helps even when I do standing race starts down in Mexico.