I am supercharging my 2TR-FE and would like to swap my 0.81:1 5th gear out for a R154's 0.753:1. Is this possible?
Not easily.
Sounds to me like you would be better off putting an R154 in and calling it good.
I'm not sure if the R154 tail housing will work on your application.
I am also not sure if The R154 was made in the later style that has the 1 piece 5th fork.
It is easy to tell if it is early or late by counting the center plate bolts. All R-series transmissions have 10 center plate bolts. The early ones have one bolt that is longer than all the others. It's located high on the passenger side.
Late models have 10 bolts that are all the same length.
Not much is compatible between the two. Even the center plate is different.
The same goes for the 1st gear. I would like to change out my 3.95:1 1st for the R154's 3.251:1 or R150's 3.830:1.
The Constant run teeth on the input and counter are only half of the equation that determines 1st gear. It's not as easy as just switching out 1st gear.
Changing 1st gear to that of an R154 requires changing the input and counter.
That requires basically switching out every other gear.
I'm pretty sure any early style 5th gear set will physically fit in any early style transmission, but not in any late style, (and vice versa) but be careful because because it is possible to wind up with a 1:1 5th gear, which would be the same as 4th.
I've worked out several different ratios that will work, (and I can get you a list) including Both a combination of gearing where you could get a 5th gear of like 0.51:1 or something insane like that and also a combination where fifth gear is actually lower than 4th gear, so as you were accelerating you'd shift 1,2,3,5,4, and 4th would be your fastest gear.
If you are that serious about changing gears to an R154, I would just get an R154 and make that work. I don't like R154's besause they are so rare and they have a high tendency to burn up the constant run teeth.
In my opinion, you'd be better off with a late model R150 out of something with a 3.4L engine.
Or...
Changing the Ring and pinion.
If the gearing options are available you could achieve basically the same goal a whole lot easier and faster.
You may already have the highest ratio available, but it's something worth looking into. Taller gears are normally stronger too...
Hope this helps.
Let me know if you need specifics
