915 Tranny ID

I recently came across a rebuilt 915 tranny but don't know much about it. Were there different versions of this box with different gearing? Is there any way to visually tell what years it would be original for?

I am sorry I can't be of more help, but I do know that there was a difference in gearing between the 1972 and 1973 915. I don't know what the markings were, but I think Warren is more knowledgable than I and will probably answer this.

Yes there were differences!

If you find the two numbers stamped on the bottom rib forward of the drain plug, we can tell more about it. One should appear as 915/xx and the other 7xxxxx. '72-'74 had 7:31 (4.429) ring & pinions, and '75 and later 8:31 (3.875) ratios. The series number can help pin down what five ratios it was equipped with originally.

------------------
Warren Hall
1973 911S Targa

OK - Here are the numbers:

915/63
7403971

What does that tell me?

Well, that is a later number series than my '72-'83 repair manual microfiche covers, but I have every reason to believe it has the 3.875 ring and pinion, and 3.18, 1.83, 1.26, 1.0, 0.82 just like the 915/61 trans in the '83 models.

Based on my June 1984 Microfiche set info, it would have to been originally for an '84, '85, or '86.

------------------
Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 04-25-2000).]

That'd make it geared taller than the early ones. Perhaps after '83 they may have made them even taller, but my '83 does about 145 mph at 6300 rpm. I don't spend much time at 145 mph.

Super:

Quick question: Are you using only your speedometer to check that you are indeed going 145?

Reason I ask is that Porsche says that the top speed of the 1983 SC is only 135, and I had my car on the Pocono Raceway tri-oval, and it topped out at 139 MPH. Also on the Charolotte Raceway oval, it never got above 139. I know that there are individual differences between 911 Sc, but it sounds like you have an optimistic speedo, or else there have been some mods to your car.......Andras

Andras, here is the evidence. On page 21 of the Porsche Family Tree boolket (PCA the 81-83 SC is listed as 146mph. The table says the numbers were complied by Porsche AG, then something about world wide markets. Okay, so I'm thinking maybe this means, ROW.

But then I peek at my Owner's Manual which seems to have survivled two POs. As mentioned by someone else in an earlier thread grapohs with rpm on the y-axis and speed on the x-axis are LINEAR and easy to deal with. That graph shows about 140 at about 6300 rpms, but the car's 'governor' (fuel pump shutoff) does not kick in until a few hundred rpms later, maybe 6800 if I recall correctly. I think that, under load these rpms are permissible. In fact I was amused to see in the Owner's Manual taht the maximum permissible rpm is 6500 plus-or-minus 200, and that 6300 rpm is the maximum CRUISING rpm.

The Owner's Manual table says rear tires used were 185/75 15s. Mine are 225/50 16s. Perhaps this is the diference.

My recollections of the tack/speedo relationship are consistent with these figures, but I recently discovered my speedo lies. My engine and tranny are on my garage floor, but I am getting pretty anxious to reinstall. I will be HAPPY to do a study from the area between the seat back and the steering wheel.

------------------
'83 SC

Andras and Super,

I ran Super's specs in my Gears915 spreadsheet and came up with a chart you guys may want to see and check. It does come out to 146.5 mph at 6300 rpm, and 140 mph at 6000, using 24.88" for effective diameter of a set of 225/50-16 tires. I guess Super's top end would depend on his tach. reading, and how accurate the tach. really is ... my guess/estimate is that 'stock' SC's can't pull 6300 rpm in top gear. If you guys want a copy of the chart in JPG or GIF format, email me, and I will send you one!

------------------
Warren Hall
1973 911S Targa

While I am very impressed with my car's ability to 'pull' well from higher speeds (70-80-90), I don't doubt that 6300 rpm in 5th gear would be a struggle. Can't imagine that it wouldn't. But I'm not embarrassed if my car "only" does 139 or whatever. In fact, I would be proud to announce a 120mph figure if I had the "fun" pack of gears. It would go from 60 to 80 in no time at all, which is more useful anyway. I'll e-mail you, Warren, as I have an insatiable hunger for info about my car.

Warren, post again if you didn;t just get an e-mail from me (trying to learn how to use these new technologies).

------------------
'83 SC



[This message has been edited by Superman (edited 04-26-2000).]