915 5th gear mod for those with a 3.6

[Joe Bob]

Looking into the future.....if I ever do another engine pull....I would consider putting in a taller 5th gear.

The 3.6 has tons of grunt and would not be adverse to having lower RPMS at freeway speeds and potential higher top speed within the power band before HP and wind say 'no mas'....

Anyone been there & done that? What 5th gear have you used....AND....is it a common gear not one that has to be specially made.

[fetus]

I don't have personal experience, but the consensus is to use an early 7:31 915 29:21 fifth gear. This would put 80 mph at 3k rpm's.

[Matt Monson]

What he said. Try to find a 29:21 TL 5th gear from an early 70's box that isn't worn out.

[Joe Bob]

Good suggestion, someone else offered a 5th from a 912E box....923? What ration is that?

[fetus]

I did a search on Pelican and it looks like a 912E also uses the same early 29:21 fifth gear.
912E.............................................. .................................................. 912E
1976 (5-Spd) 11:35 11:33 23:29 26:25 29:21 7:31

[ToddM]

Assuming this is a street car... I can see why you'd want to do that but I kind of like having the power available in 5th at speed and the 3.6 definitely doesn't mind cruising at 4K RPM on the freeway.

This probably has a lot to do with how congested your freeways are/aren't as I need to frequently take evasive action to avoid others not paying attention; on an open freeway and to get a higher top speed definitely would be nice.

Until I get my new shifter installed, my biggest fear is avoiding the shift into 6th that isn't there when I am in la-la land being that my daily driver is a modern 6 speed.

[Joe Bob]

I can't tell you the last time I have spent for than 30 seconds in 4th gear. Half the time I simply shift from 3rd to 5th.

Having a true overdrive 5th would reduce the rpms on the rare occasion where I have a clear road ahead of me. If and when I ever do open the box again, I will consider modding 4th AND 5th.

[T77911S]

Originally Posted by Joe Bob

I can't tell you the last time I have spent for than 30 seconds in 4th gear. Half the time I simply shift from 3rd to 5th.

Having a true overdrive 5th would reduce the rpms on the rare occasion where I have a clear road ahead of me. If and when I ever do open the box again, I will consider modding 4th AND 5th.

i do the same. i skip gears ALL the time around town, most of the time it is 3rd for me since the syncro is bad and there is no need to go through 5 gears to get to 60 mph.
i have considered a good function 4 speed with a true "overdrive" 5th, but then i think about how many trips i take in the 911 and think it not worth it.

the one long trip i took, south carolina to nashville, i hated how hight he RPM's were, well, it did sound good but nearly 4k for 10 hours.

[fetus]

There is also a 29:22 fifth gear. I have seen them on eBay. A 29:21 is 3k rpm's at 80mph. A 29:22 is 76mph at 3k rpm's. Stock I think is 70mph at 3k rpm's. There was an article in Excellence with a 3.6 and a 915 in a 914 and he changed 1st, 2nd and 5th. He used a 29:21 for 5th. A 914 is around 500 pounds lighter though in GT trim.