Interested in knowing if gearsets and final drives are compatible among all D-series transmission cases? I am specifically in knowing if a Civic/CRX Si gearset & final drive would work in a STD 4-Spd case or would the case have to be a 5spd?

I have found a gearset and final drive for a Si cable and wondering if it would be purchasing and in what case it would have to go.

Thanks in advance!

 

The Si internals will work fine.

The 4spd is a 5spd trans with a few changes: spacer collars in place of 5th gear and 5th gear sleeve assembly, different shift fork rods and no 5th gear shift fork, no reverse lockout.

Swap the gear stacks and ring gear to the 4spd case along with the shift fork assembly and add the reverse lockout in. You'll need to shim the mainshaft.