911 transmission?

[bumble]

We all know about 901, 915 and G50 transmissions, but I was talking to someone recently who claims to have a 911 transmission - apparently this is a stronger 901 transmission made for only 2 years. Does anyone know if this is true? Details?

Mark

[Flat6pac]

Yes, it is numbered as a 911 transmission. It is a 901 with a different clutch package, larger, and a different throw out bearing system. Only used for 1970/71. Predecessor of the 915 clutch package.
Bruce

[Bill Verburg]

here are a few pica of early g50, 915, 911 and 901 trans

[bumble]

Bruce, Bill - many thanks - I am now slightly less ignorant

Answers, however, beget further questions. The conversation was in relation to big HP engines in a 914 - the gentleman in question has changed to a 915 and has two 911 transmissions surplus to requirements - one disassembled and the other complete with LSD and rebuilt with new bearings etc. $7K for both which sounds reasonable (although maybe not for my bank manager ) So the question is - are they significantly better than the 901 (and why), and what would be required in terms of clutch/cable adaptation?

TIA - Mark

[Grady Clay]

Mark,

Without knowing the details, that sounds very expensive.
I would carefully investigate all the internal parts of both transmissions.

A 911 transmission is virtually identical to the 901.
It has the later magnesium castings. You want the version with the rectangular boss for the numbers.
The internal gears are identical or interchangeable to 901.
The type 911/01 is originally geared A-GA-O-V-ZA.
The R&P choice is 7:31.

The big difference is the larger differential, common to 915, 930 and more.
That LSD uses 917 part number pieces.

Another important difference is the ability to use the larger 225 mm pull-type clutch.
While the clutch operating linkage in a 911 is very “Rube Goldberg”, in a 914-6 application, a slightly modified arm does away with the cable pulley.

The general consensus is that 2.8 liters is about the limit for longevity using a 901/911/914 transmission. (2.2 was the largest engine Porsche used.)
For competition and pushing the limit of this transmission, an oil cooler, pump & filter will significantly add life and many consider necessary.
If “big hp engines” include 3.0 and larger or much above 250 hp, a 901/911/914 is not up to the task.
Yes, many have run 3.0 and larger through these but I would not. I don’t like broken and prematurely worn transmission parts.
A 915 or 930 can be adapted for a 914-6 with “big hp engines”.

I have a type 911 in my street 914-6 (2.8S MFI) and my CP/GT2 914-6 racer (2.6R).

Best,
Grady

[bumble]

Grady, thanks for your insight.

Yes, it does sound a little expensive, but I know how much it costs to do the right job on these transmissions and assuming they are as represented, $7K is not unreasonable for two transmissions with LSD, short ratios and new parts. Of course, it would all need to be verified...

The guy has a long stroke 2.9L engine (specially made crank) which reputedly turns some pretty impressive power/torque numbers (i.e. way more than 250hp) so it's not surprising given your information that he had longevity problems.

I currently run a sweet little 2L engine and a very well developed 901 (magnesium) with Quaife, billet intermediate plate and some other mods we've done for longevity and never had a problem, even when I had my earlier 2.7 engine.

With an eye to the future, I am contemplating rebuilding my 2.7 into a 2.9 with a 270-280hp goal and don't want to use my current transmission - but I also don't want to lug the extra weight of a 915 around either (not to mention the cost of 915 adaptation to the 914). So, knowing that the 911 would be marginal in this application, at least I know the associated risks

Mark