All,

I'm doing a bit of research for my FC road racing friends from the ITS series...can we swap in ratios from the 79-85 series cars into NA 2nd gens bc all I find is a 4.30 rear and some of these tracks could use shorter gearing since the NA motors are so low on torque. The 79-85 boys can swap in anywhere from 3.90 - 5.12 gears, now THATS adjustability...are the NA FC's at all interchangeable with the FB tranny/rear? BTW, we run a 325I at Z-1 Performance and the FC's regularly SPANK us even though we outpower them severely...they just maintain speed and balance so well, our head driver wants me to strip my street NA FC and toss in a cage and slicks (all my other mods are legal for the series, even my type coilovers and camber plates - but I'm goin the TII swap route thanks to Kevin Landers...the motor he built for me is just sitting in our shop for the past few months waiting for me to get the time to swap it in hehe). The 4.30 rear from the GTUs won't do it for these boys, they need more hehe

Thanks!!
Jon

 

Your answer is no... the FC is stuck with only three ring and pinion sets... 3.909, 4.100 & 4.3 and the N/A ones are not interchangable with the turbo gear set.

An alternate would be to graft a 1st gen pinion shaft onto the 2nd gen shaft
Or there is an adapter kit which allows the use of 1st gen ring and pinion gear sets.
A TII swap should take care of the need for more bottom end...but not in ITS class

 

I have heard of some people adapting the '94-up Miata to the FC. *Should* only require fabricating a new front diff mount to the Miata's PPF mount holes, and a longer driveshaft. The Miata 7" uses the same gears as the 1st-gen RX-7 as well as some "other" vehicles, and all '84-up Mazda 7" use the same axle shaft splines, be it solid axle or independent.

The tranny in the N/A FC is the same as 1st-gens, although the FC ratios are closer than the 1st-gens had. 5th gear can be swapped over but the ratio would be different as the transfer gear ratio (from input shaft to countershaft) is different between 1st-gens and FCs.

Miatas have even closer ratios, almost the same as '79-82 626's. Which all also use the same "Type M" smoothcase transmission.

 

you could try a machine shop