Was the R180 only used on automatics or did they put it on 4 speeds too ('70-'72). Also is the R200 considered a better rear end and if so, why? I'm trying to figure out the original setup on my 240 and what year it is too...
All 240Z's came with R180s. R200's weren't introduced until '75 (I believe..) on manual transmission cars to handle the extra torque in the 280Z engine.
R200's are valued because they're stronger and because if you're looking for a higher ratio such as 3.9, it's usually easier to find it in an R200. Unless you have a turbo, V-8, or you do a lot of drag racing you probably don't need the added strength of the R200, so an R180 will be just fine. It's lighter, as well.
Good info on all the rear ends. Now, with a 3.364 R180 in my 4 speed, I'm at about 3600 rpm at 80 mph. It seems like a 3.9 would take me up to about 4200? That seems a bit high for just cruising (I do a lot of highway driving). It seems like I wouldn't want to go higher than the 3.545 or possibly the 3.7? Any thoughts on rear ends in a 4 speed?