Re: Recommend diff ratios
I'm guessing you want to be around 3.54 a balance between off the line and top speed. I wouldn't recommend anything lower unless you plan on driving in a straight line or you completly updated the suspension.
Use this formula to figure out were you want to be
Maximum MPH in each gear:
Formula: MPH = rpm x tire diameter (in) / gear x final gear ratio (diff) x 336
Example: Maximum mph in 280Z 5spd 1st gear using 6500rpm redline.
MPH = 6500rpm x 24.0"(tire dia.)/ 3.321(1st gear) x 3.54(diff gear) x 336 = 39.5mph
Note: Top gear is most likely hp limited, and would not be able to reach max rpm.
RPM @ 65mph (Derived from Max MPH formula):
Formula: RPM = mph x gear x final ratio x 336/tire diameter
Example: RPM at 65mph for stock 280Z 5spd
65mph x 0.864(5th gear) x 3.54(diff gear) x 336/24.0"(tire dia.) = 2783 rpm