I am about to install my 3.2 engine and it is being paired with the 901. I was wondering if the 901 need to be regeared or use heavier gears for this application or is the standard gearing fine?

Any other things that should be considered?

It will be for street only.

standard what?
/4 and /6 are different...

There are no heavier/thicker gears so that option is out...

In The Beginning, /6's had a shorter top gear (ZA vs ZD) than the 4's to make better use of the rev range and spin the engine a little faster for improved cooling airflow at highway speeds.

However, by the time 911's sprouted 3,2's, gearing was getting tall again - in part I suspect for highway fuel economy numbers and in part because synthetic oils could handle the heat better. I have a 915/67 from a Euro Carrera 3,2 and it is geared VERY tall in top - the better to travel the Autobahn ;-)

With that in mind, you might actually be better off with standard /4 (ZD top) gearing. The rest of the gears are actually pretty close, except for 2nd, which you can't change without finding a 914.6 mainshaft anyway...

But if you find you do need something special, Guard Transmissions is making 901 gears now - call Matt and tell him what you need...

I went from a 1.8 to a 3.2 and kept the same 901. 4 years no problemo.

I think it came from a standard 4. Sounds like finally I have something that does not need adjustment to take the six.

Well Wills moved his redline to 2500 RPMs.....sooooo, take that in account

haha, j/k

What you end up with is a 4 speed for that car. 1st will be so low it will be almost useless. In addition, if you stand on it in first, you will eventually break it so it won't get used much.

Gears and modifications are expensive and I would save your money and invest in a 915 if you want something re-geared and/or stronger.

I would rebuild and keep the 901 fresh and not invest a bunch of money for gears and improvements and if you blow it, throw another stock one in until you go to a 915 and then build the tranny with the gearing and modifications you want. It's VERY expensive to change gearing in either transmission but I don't see the practicality of investing in a 901 for big HP.

My 915 has a tall first, an "overdrive" for 5th and close between 1-4
53mph for 1st
81mph at 3000 rpm

It's expensive to do but it extracts maximum performance from your conversion.

There are plenty of people running 901's and plenty blow them up too but if you are willing to live with a mediocre setup, they are cheap to buy. Let your pocket book be your guide......

I've been running a 3.6L since 1999 and it's fine. Be smooth.

It depends on the condition of the gearbox. A good freshly rebuilt box will work fine with a 3.2, as long as you don't bang 1st gear.

I did a 3.0 conversion with a stock 901 and that was drove hard smoothly, and it's still doing fine without any problems, 16 years later.

A few years ago I did a conversion with a hot rod 3.2 that was around 250hp, and that's still going strong too.

Both transmissions were completely rebuit with all new bearings and syncros. One had a 901 limited slip and the other had a Guard torque biasing diff. Both cars had/have big tires and the 3.2 had several DE's time trials, and track events.

What Perry talks about is pretty much the extreme; LSD = more stress on the tranz guts. It worked well for him and I would not hesitate to do the same. You can save some money and weight by pitching 1st gear. If the slider is in good shape, you can sell it for a few $$$ and cover other parts. At least, that is what I do. HP is not the killer, TQ is when it comes on too fast (burn outs, etc). Stock /4 gears will be fine. I have built 901 boxes for race 3.0 engines that have not missed a beat.

Come to think of it, I have never had a box come apart in a non-stock application.

Has anyone here first hand experience with blowing a box with a bigger motor??? I have not seen that happen if the CVs are stack as they break first. Just my "limited" experience, YMMV

Good stuff. I will be putting a stock 3.0L into my 914 sometime this year...sticking with the 901. I'll probably keep the 915 out of the donor car as a backup.

How you drive is the key to how long it will last.

My street 914 with a 3.2 should last a good long time. It isn't pounded on and it was fully rebuilt with a billet intermediate plate with new intermediate plate bearings. All the gears were inspected and was properly set up.

Having said that, I have also torn up MANY 901 gearboxes with the track car (also a 3.2).

Every failure we had was with 4th gear losing teeth. After each failure, I could really find no reason for the failures. The bearings were always good, the races tight in their bores, but investigating the cracks in the roots of the gears showed evidence of fatigue failure.

It is assumed that the shafts could have been bending allowing the mesh of the gears to change but this was never confirmed.

It was also assumed that heat may have played into the general scheme.


The broken gearboxe(s) were in a DE track only car with 2 advanced drivers/instructors. The failures started occuring after we both had approximately 15 years experience with the car.



We went with a 915 box (with the WEVO 915 reinforcement bits) and have had no other failures.




Like I mentioned in the beginning, it depends on how the car is used. I believe that they will survive for a long time on the street, but for heavy use (track use), something else needs to be considered (at least for long term use).


just my $0.02

No one has mentioned adding a trans lube and cooler system to your conversion which will surely prolong the life of a transmission. Street use and racing are completely different animals as road racing puts a huge amount of stress on the gear box which is why many go with the lube system and plan a 901 overhaul each winter. You can use a 904 input shaft and run the much higher 1st gear (actually 2nd) so you will get a real usable 5 gears but that will cost as much as your engine probably? Many of the vintage racing 2L Porsches ran a 901 box with limited slip and they were putting about 200 HP to the rear wheels and a tranny would last about 2 years max and need an overhaul. If the engine jumped up to a 3.2 or 3.3 and had 275 rear wheel HP then the trans might only last one year max. A 915 box would last about two years racing but then need an overhaul and in the end over a 5 or 6 year period total cost was the same! For street use the 901 should do fine as long as it is like new inside, shifted easy, use a Rennshift
and don't do burnouts!

A cooler is essential as far as I'm concerned, in the south. Even on a street car and especially with limited slip.

If these boxes had coolers and pumps in them from the factory, other than obvious driver abuse like speed shifting (hell on spiders and sliders), they would last longer.

And for those who run synthetic gear lube (a controversial topic at best) temps will come down even farther.
Everything's better cool!

Where would you mount it?

Great info on here, had no idea a 3.2 could be matched up with a 901...gets me thinking....haha.

Yeah, how/where do you mount a trans cooler?

There is plenty of space back there but exhaust heat makes that a sticky wicket. Some have mounted it in and under their rear trunks and are fan-cooled, while others have them mounted behind the transmission and between the twin exhausts. Note: If you have a stock exhaust that rear mount space is taken.

Cool air can be gotten from wherever you can find it and ducted into the cooler. Sometimes that's the rear wheelwell, sometimes its a naca-duct or scoop in the rocker covers, or a scoop mounted somewhere else. Just remember, naca ducts aren't designed to give you a whole bunch of air. If your temps are too high then a fan is needed.

Let's talk about what components you need to use and some examples...

Pump: Weldon (high dollar), Tilton, Mocal. A reversible pump will allow you to run it backwards and drain the transaxle without opening a drain plug

http://www.weldonracing.com/product/54-7/9...e_Oil_Pump.html

http://www.racerpartswholesale.com/categor...ial_Cooler_Pump

Filter: Canton Mecca, other. High-flow filter with replaceable cartridge. Makes it easy to see how much metal you're rubbing off and protects your pump and cooler.

Cooler: B&S, Earls, other.

Hose and fittings: Aeroquip, Earl's, or high temp rubber and brass fittings. The latter are higher maintenance but cheaper. I recommend -8AN stuff. Good flow and it'll tolerate heat better, especially when wrapped.

Check valve: Canton Mecca, other. So the flow can't back into the case. Needed if the cooler etc. is mounted higher than the transaxle... normally the case.

Machine work: At least the inlet will have to be tapped into your case. For the outlet you can use the drain plug hole and a (non-magnetic) 915 plug tapped for a fitting (in my case a -8). The 915 plugs are a hex's and "outties" rather than the "innie" plugs 901 and 914 cases have.

Overflow canister: might not need this but it has to be vented and the outlet fitting will go where the current vent is in teh top of your case.

Non-useful (for most of us) note: Some factory 915's have the finned cooler-loops sticking out of the passenger side of the transmission and is a coil-looking affair. But it has an internal pump too. Since it's under the diff fluid level it doesn't need a check valve.

Good luck

Lots of good info and suggestions here. I think it's important though to have a distinction between what will work and what is ideal. People use 901's behind everything including V-8's with the same issues I brought out earlier. Loss of 1st gear and a low 5th for big HP applications. Will it work? Sure. Will it survive? Sure, if taken care of.

I think the best thing I did on my conversion was to spend the money on gearing the transmission (915) appropriate to the hp and weight of the car. When you put 300 hp in a 2200 lb car any transmission will give you a thrill. However, a properly geared transmission will take that experience to a new level. The power, torque and driveability come to new levels when properly geared. Proper gearing makes a fun car into a great car. Can you have fun with a stock 901? Absolutely. You'll just have MORE fun when it's properly geared.

So.... when you see threads debating the use of 901's, keep in mind the difference.

By the time Porsche released the 3.6 they had already moved past the 915 to a G50 which is even stronger than a 915 which is significantly stronger than a 901. Again will a 901 work? Sure.

My point is that I personally wouldn't spend a ton of money on a 901 for big HP applications for gearing and upgrades when that money is better spent on a stronger transmission. But that's just my opinion. If money was tight, I wouldn't hesitate to run a 901 and if it broke I wouldn't feel bad since they are cheap to buy.

Unfortunately building a 915 and adding a WEVO is cost prohibitive for many and the cost of the tranny might exceed the value of the car. Rebuilding a 901 on occasion is cheaper and easier, it just loses some of the "fun factor" and doesn't optimize a big 6 in a 914.

So, the debate will continue and the wallet will be the master of our decisions......

The beauty of an external cooling system is that it's still there and cooling no matter what transaxle you put into the car!

Great Stuff Guys-thanks for your help.

got a stock 901 in my 231 Cu in. (3.8 liter) Buick powered 914, no probelms so far, I hammer it sometimes, (but not in first) couple hundered HP there

Here's a pict of the car car mounting. I went the slightly more expensive route and bought a complete setup from Jim Patrick in Phoenix as I wanted to get in in before a race in Tacate MX in August. The air inlet is at the front of the right rear flare. You do have to drill and tap a pair (at least) holes on the top of the gear box, one over the gear stack and one over the R&P so there will be lots of oil splashing on those hot parts.

Patrick also sells a plug that goes into the speedo drive holes and a temp gauge so you can keep an eye on things as we all know anyone with a hot rodder 914 does not pay attention to the speedo anyways!

This also let you run a full 4 quarts of trans fluid instead of the factory amount.

Pretty

Pictures?

many people will also tell you that each "newer" transmission shifted worse and made driving less fun.....

plus the newer trannys definitely got heavier... not ideal for a race car

there is something to be said for light weight.. esecially on the track!

It is at paint now. Flares went on last week. Will have pics next week and pics of the new engine.

I am one of those guys who likes the relatively 'light' shift effort, pattern and weight of the original 901-type trans. My application has been behind peaky fours and sixes that do not slam it with low-RPM torque, but I've been using my current short-geared and fully sorted box for track events (not a whole lot unfortunately) since 2004 without probs.

At some point, esp. if I start doing a lot more big/fast track events, I will very likely add a cooler as John discussed.