differential compatibility?
 

so i found a GTU FC at the bone yard and from what i've read this car came with the 4:30 gear ratio in the diff,
so the question is, would this third member swap into my FD? what would i need to do it? ring and pinon compatible?

i gotta figure something out, my auto fd is a PIG off the line.

The third member is different because the FD has a Power Plant Frame. The ring and pinion may be compatible but I don't know for sure. Might want to research on the GTU more because I believe it just has a regular TII rear.

All of the automatic RX's are terrible off the line, I sure don't miss it. You might want to look into the manual swap, it really changes the way you think about your car...

The ring and pinion will not fit. The hole diameter on the second gen ring is about 2" smaller than the stock FD. If you want taller gears look for an RX-8 ring and pinon or look for a used set of 4:30's.

thanks good to know. so the rx8's came with 4:30's?

i'd love to do a manual swap but thats gonna be outside the budget for quite some time

The only FC that came with 4.30s was the 89-90 GTUs. Hard to find for sure. The S4 GTU came with a 4.10 clutch type LSD while the S5 GTU had a 1-legger.

Also the GTU and GTUs was only a 7" ring gear.

Only the T2 and FD diffs were 8" ring gear.
FC was a long snout pinion gear and FD was short snout. They are not interchangeable.

The FC T2 LSD unit and vice versa FD LSD can swap back/forth into either diff. You do need to shim/space them properly. S4 T2 LSD is the strongest factory unit out. Kazz is basically the same as it but is made from better/beefier material in the case and also thicker/larger clutch packs.

no rx-8's come with 4:44's not 4.30. several manufacturer's made aftermarket ring and pinion for FD's with 4:30's. You can sometimes find them in the fore sale section

would rx8 4:44s work in an FD?