901 or 915...that is the question...

[Carrerax]

Im restoring a 1970t and am on the fence regarding the transmission. Im building a 3.2ss with PMO's it should make approx 250hp. As much as I want to keep my 901 I fear it will live a short life. A few people have said to go to a good rebuilt 915 for a longer life but I really prefer a 901. Cornpanzer and I have had this discussion several times and Im trying to make a decision.

Im looking for some replies from people that have had a 901 with 200+ Tq motors and lived to tell about it. I am not going to drive this car like a teenager but I am also going to enjoy it. It will see a few track days but will mainly be a nice street car. That said, I will baby it to a point but I also dont want to fear its demise when driving it. Basically Im asking to be talked out of buying a good rebuilt 915.....Thanks! All replies are appreciated!!!

[ttweed]

A 901 can be built to withstand 300 HP, but it will take some $$$ and still require babying it in 1st gear. After seeing the 7:31 R&P thrashed in an early mag case 915 running behind a 218 RWHP slightly modified 3.2 Carrera engine, I would not settle for anything less than a later aluminum-cased 915 with an 8:31 if I was in your position, and I would still modify it to be stronger and more reliable, but that's just me.

YMMV,
TT

[Flieger]

I think the 901 road racing shift pattern is cool and they are lighter. I would use the 911 box. If it breaks, then you could get a 915. They have their problems, too.

[tomkirkcis]

I am running a 3.2SS in a 914-6. I have a 901 box with A-F-M-S-X and a zf LSD. I did have a billet intermediate plate and a billet bearing retainer installed when it was rebuilt.

First gear clearly is the weak spot. My thoughts on drving are the same you expressed. A few track days but mostly street and trying to be smart ( a 3.2ss in a light body car is hard to drive smart ) I expect to have to freshen the box more often than I would a 915, but it is a lot easier than doing the swap. If it was a DE car, I would recommend the 915.

tom

[John Z Goriup]

A 901 can be built to withstand 300 HP, but it will take some $$$ and still require babying it in 1st gear. After seeing the 7:31 R&P thrashed in an early mag case 915 running behind a 218 RWHP slightly modified 3.2 Carrera engine, I would not settle for anything less than a later aluminum-cased 915 with an 8:31 if I was in your position, and I would still modify it to be stronger and more reliable, but that's just me.

YMMV,
TT

That is the soundest piece of advice of all these replies yet.

If you need additional persuasion that an aluminum-cased 915 is the logical, reasonable & reliable choice, answer one simple question, please: --Why go to the trouble and expense of building a short-stroke 3.2, which will in all probability make more than 250 HP at the flywheel, and then have to baby it to protect the 901 box ??? What would be the point of entering into a project knowingly creating a powertrain combination which would prevent you from enjoying the full spectrum of performance the engine offers.

I can assure you from personal experience that a carefully built, well-speced ss 3.2, with correctly sized PMOs ( and SSIs, modified sports muffler, recurved distributor, & the right heads ) will exceed 250 HP, and produce 230+ ft. LB. of torque. That's just too close to the to max. capacity of a stock 901 and I submit that sinking the necessary amount of money for the required modifcations into a 901 is a risky and questionable investment.

[Mr9146]

3.2?

915.

[Flieger]

My 911 felt great with the road-race shift pattern on our drive around the twisties today.

It started- I think it must be an intermittent wiring issue.

[Carrerax]

That is the soundest piece of advice of all these replies yet.

If you need additional persuasion that an aluminum-cased 915 is the logical, reasonable & reliable choice, answer one simple question, please: --Why go to the trouble and expense of building a short-stroke 3.2, which will in all probability make more than 250 HP at the flywheel, and then have to baby it to protect the 901 box ??? What would be the point of entering into a project knowingly creating a powertrain combination which would prevent you from enjoying the full spectrum of performance the engine offers.

I can assure you from personal experience that a carefully built, well-speced ss 3.2, with correctly sized PMOs ( and SSIs, modified sports muffler, recurved distributor, & the right heads ) will exceed 250 HP, and produce 230+ ft. LB. of torque. That's just too close to the to max. capacity of a stock 901 and I submit that sinking the necessary amount of money for the required modifcations into a 901 is a risky and questionable investment.

Thanks for replies guys. The motor is a 3.2ss (Max Moritz p/c's) with new 46mm PMO's spec'd by Steve Weiner, Mod S cams, twin plug JB distributor (also built to Steve W specs), early 3.0 large port heads heads also built by Steve W and SSI's with a Dansk sport muffler. John Truman is building the motor. Hopefully it will make decent power. I have to agree that as much as I like a 901, I really dont want to have to be overly cautious with the transmission when Im enjoying it. Also, I am going to have to spend $2-3k on the 901 or I can just get a rebuilt late 915.67 for about $4k and be done with it. I do hate the thought of bastardizing the car but I think I already did that with the 3.2.

[sithot]

They never made a sweeter shifting box than the 901. It has its weaknesses but 1st gear is out of the "H" for a reason. It's a pure race pattern.
I love mine but I'm only making half the horsepower. For sheer fun on a back road you cannot beat it.

FWIW; Bobby Smith has a 4 cylinder engine that has a torque curve approaching 225 ft lbs. His 901 has been at it for as long as I can remember. If you're mistaken in believing that torque won't damage something, think again.
1st is for drag racing. Once you're rolling you shouldn't see again on a race track.

You can tear up any gearbox if you abuse a launch in the 911. They hook up like nothing else. Bobby told a story of a guy with a hotted up 3.2 tearing up a 901. He asked "how he did it?" He answered that he was "drifting and it hooked up". DOH!

I thought I'd heard it all. A Porsche subjected to drifting.

Tom

[kenikh]

Build the 901. The 7:31 RnP is the weakness that matters most, as 1st is easy to not beat on. I heard from Jamie Novak that Matt Monson just announced an RnP that will take everything you can throw at it. 901 is a much sweeter box.