915 Stock Gearing - SC vs Carrera - same or different?

[RarlyL8]

Something goofy going on here.
I have a '78 915 Euro tranny from my SC and a 915 Euro tranny from an '84 Carrera.

At 80mph in 5th the '78 tachs 3500rpm while the '83 tachs below 3000rpm.

My Porsche manual shows these two trannies as having the same gearing. Am I looking at US specs vs Euro? What's the story?

[Bill Verburg]

They do not have the same gearing in the top 2 gears, the '84 is more highly over driven and will show lower rpms at a given speed

'78 915/61 all markets
11/35 18/33 23/29 26/26 28/23

'84 915/67
11/35 18/33 23/29 29/28 38/29

[RarlyL8]

Thanks Bill.
Where do you find the gear numbers (ex: 11/35) on the gears themselves? I have the '84 box down for repairs and would like to know exactly what gears are in it. I suspect they have all been changed, NONE of the gears run the same speed/rpm as the '78SC box.

[Bill Verburg]

Since it's apart wouldn't it be as easy to count teeth?

[RarlyL8]

That's too easy. I thought these gearsets had alphabetic designations, seems like I've seen charts where they were listed by pairs of capital letters. I'll look this up in my manuals.
The '84 gear box has the R&P removed right now, haven't gotten into the case yet. No reason to spend time looking for letters or numbers if they aren't there - HA!