More ratio madness (901), 2nd gear flipped 5th gear who knows huh? Options

[bondo]

Ok, so I now know that for a good v8 5th gear, I need to put second gear in it's place.. flipped. 2nd gear is one 18 tooth gear and one 34 tooth gear. The 18 tooth gear is part of the mainshaft and not removable.

Then someone said the 904 mainshaft has no gears machines into it and all are equally swappable. But that is very rare, right? It's also more than I really need, as I just want the gear.

But then it's been said that a 912 4 speed transmission has first gear where 2nd is on a 901, and the second gear is where third gear would be on a 901. Presumalbly this second gear is removable, and has the same splines on the inside as 901 gears. Is the ratio of this second gear something close to 18:34? Anything lower than 22:31 and it wouldn't be any taller than the stock 901 5th gear once it's flipped. I need sure answers here, I bought two 901s (no biggie, cheap) based on a statement something like: "you just flip 2nd gear and put it in place of 5th, and voila, taller 5th gear" which turned out to be nearly (see my signature) impossible. I do not want to buy a 912 4 speed to scavenge 2nd gear out of only to find it won't work or doesn't have the right 2nd gear ratio. (expensive)

Just for the distribution of useful information, here are the ratios (tooth counts) of the stock 901 out of a 914 (side shift, but I don't think that matters)

1st (didn't count, but can if requested)
2nd 18:34
3rd 23:29
4th 27:25
5th 31:22

R&P 7:31

[davep]

And you might consider using a 912 case which is rated at 400HP vs the 901 which is rated at 300HP.

I'm not sure where you got this information. It may be true of the 912E case that was basically a 915 transmission. The original 911 / 912 / 914 cases were very much the same; a 901 type unit. In 70 and 71 the 911 used the 911 type tranny that was very similar to the 901. From 1972 the various flavours of 915 transmissions were used and these were much stonger.