901 trans

Lars Torvik · 02-28-2006, 11:11 AM

Which parts break in a 4sp 901 from 350 HP

jpnovak · 02-28-2006, 11:19 AM

First gear shear from the main shaft? worn intermediate plate and bearing supports? ring and pinion? That much power could produce a long list of problems.

Lars Torvik · 02-28-2006, 01:28 PM

The problem 1st gear is only in the 5sp boxes which also contrbutes to the intermediate plate weakness due to the pressure from a 1st gear supported on one side. A reinforsed side cover would help the R and P and a LSD would take care of the spider gears

Grady Clay · 02-28-2006, 02:11 PM

Lars is right on.
However, the best choice is a 915 or 930. Depending on the use, a 901 isn’t capable of those numbers, There is a reason why Porsche changed transmissions over the years. If you have a really big engine, try a type 912 transmission. HeHe.

Best,
Grady

jpnovak · 02-28-2006, 02:18 PM

I guess I missed the 4sp part.

Grady, I suppose the 912/16 would be the best choice.

It has the strongest cwp setup.

Lars Torvik · 03-01-2006, 04:24 PM

Just because they do an upgrade should not be an indication of a inadequate part. I think the 901 has got a bad rap. Desert Hybrids agrees.(pros) they say yes to 350HP SB.

Grady Clay · 03-01-2006, 06:18 PM

Lars,

The 901 doesn’t get a bad rap, it is a wonderful transmission and my favorite. I can tell you subtle 901/911/914 details forever. The point is any transmission was designed within limits.

Porsche designed the transmissions to not leave a lot on the table. Sure, they could have built a giant, indestructible transmission for the 1991 cc, 220 hp and 2195 cc, say 260 hp cars ’65-’71. They would have been too heavy and unnecessary. In ’72 Porsche introduced the 915 with the 2341 cc engine. This transmission was an adaptation of the type 908 transmission raced in ’68. The 930 was introduced in ’75, somewhat based on the 912. The G50 and later was designed on an almost blank sheet of paper.

Sorry about the “in-joke” type 912. That is the BIGtransmission used with the 5.4L 12-cylinder 917 turbo that conservatively put 1200 hp through the transmission for 24-hour races. Even it was just within the limits for the power, torque and use.

So, what are the differences?

Between each transmission series several critical things got changed, almost all with a weight penalty.
1) The center-to-center distance between the input shaft and the pinion shaft. This makes the gear diameters larger.
2) The diameters of the shafts.
3) The size (diameter and other) of the ring & pinion.
4) The width of the gears.
5) The number and size of the support bearings.
6) The robustness of the castings.
7) Oil cooling.
8) Many subtle design features.
9) The overall size (with attendant weight).

You will get the point when you set a 901/911, 915, 930 and G50 (950) next to each other and then try and pick them up.

I have a friend I sold a nice ’72 914 roller to in ’74. He installed a SBC at about 350 hp with the best 901/914/911 transmission and it simply wouldn’t take it. He now uses a Hewland DG-800 with no problems today handling around 600 hp SBC.

I’ll encourage you to use a Porsche transmission that is sufficient for the task. To do otherwise, you will be buying a lot of very expensive parts.

Best,
Grady

SandyI · 03-01-2006, 06:47 PM

I have a friend named Otto who runs 350 HP thru his 901 in a tube-frame 914 racer. You want to go fast with that 901? Get your car to him.
Otto's Venice - 310.399.3221.

Lars Torvik · 03-01-2006, 09:25 PM

Ive looked long and hard at the 915 and 930. I would need all new gears for the 915 which cost as much as a 930, if I could find one, and I would have to cut the 930 bell-housing as I did the 901. I would have a lot of trouble treating a rare and mechanical work of art like that, yea I know I put a ford motor in a Porsche, but I'vee become a fan. So far I am the only one that's done a 911,912/ford conversion, or stand corrected. I made all the parts needed, I've been dumping the clutch for 2 years then broke the spiders. Thanks for the main-shaft tip I've been looking at the 904, and I'll check with Otto. This is a 1967 912, I would like to save the exotic transaxle for a GT 40.

Thanks, Lars

randywebb · 03-02-2006, 02:55 PM

IS there a stronger sidecover for the 901 or 911 trannies??

soupbone · 03-02-2006, 03:39 PM

http://www.powerhausii.com/products/901.html

Also would there be any strength benefit to using a PHII 8:31 R&P in a 901 instead of 7.31?

Available PHII Upgrades for the 901
HD Intermediate Plate
HD Side Plate
HD Synchro Engagement Kit
PHII Oiling System
Cryo-Rem Processing

Zeke · 03-02-2006, 04:52 PM

Yeah, but "Otto" has all but completely redesigned his trannys. Billet intermediate, custom machined 904 shaft (new, stronger all the way), the side plate, etc. Plus, John Williamson knows how to drive.

Where one man will destroy a tranny another can make it last a long time. All I'm saying is that there are some variables.