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I'm running a 240sx transmission, a 3.90 diff and a  23.5" tall tire. 4th gear (which is 1.000 in the trans) does about 54mph at 3k RPM. A more normal tire size at around 25" would get you to 57mph at 3k RPM. 


https://spicerparts.com/calculators/transmission-ratio-rpm-calculator Pretty good calculator for doing the math, once you know your transmission ratios. Can play around with rear end ratios and figure out what you want for top speed. 

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You know the diff from a 240sx doesn't just bolt up right? It's a completely different diff housing and will require lots of fab work or money for custom parts/axles.


Either way, how usable your car will be for every day driving will really come down to how tall your last gear is.

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Posted (edited)

Many R200 3.9 differentials used in Z cars.  Pick one and you will be miles ahead.............................




240Z        70-73   MT       (3.364) (R180)

240Z        70-73   MT 5spd. (3.900) (R180) - non US

240Z        71-73   Auto     (3.545) (R180)

260Z        74      MT       (3.364) (R180)

260Z        74      Auto     (3.545) (R180)

280Z        75-76            (3.545) (R200)

280Z        77-78   MT       (3.545) (R200)

280Z        77-78   Auto     (3.545) (R180)

280ZX       79      MT,4 Spd,2 Seater (3.364) (R180)

280ZX       79      MT,5 Spd,2 Seater (3.364) (R180)

280ZX       79      All With Automatic(3.545) (R180)

280ZX       79      MT,4 Spd,4 Seater (3.364) (R200)

280ZX       79      MT,5 Spd,4 Seater   (3.7) (R200)

280ZX-GL    79                          (3.7) (R200)

280ZX       80      MT,2 Seater       (3.545) (R180)

280ZX       80      Automatic 2/4Seat (3.545) (R180)

280ZX       80      MT,4 Seater         (3.9) (R200)

280ZX-GL    80                          (3.9) (R200) 

280ZX       81-83   Automatic all     (3.545) (R180)

280ZX       81-83   Turbo - all       (3.545) (R200)

280ZX       81-83   MT                  (3.9) (R200)

 - - - - 300ZX's - - - - - -- -

300ZX       84-86   MT and A/T          (3.7)  (R200)
300ZX       84-86   Turbo MT and A/T    (3.54) (R200)
300ZX       87-89   MT and A/T          (3.9 ) (R200)
300ZX       87-89   MT and A/T          (3.9 ) (R200)
300ZX       87-89   Turbo MT and A/T    (3.7 ) (R200)
            Note Turbos: 
            #1) after 4/87 only-(3.7 Clutch Type LSD)
             2) 88 All White SS used a 3.7 Viscous Coupling LSD)
             3) LSD Unites Came With Finned Rear Covers

Additional Comments: a) Viscous Coupling LSD requires special splined half shafts - b) 84-87 R200's can be used in earlier cars, but require modifications they are not direct bolt in swapable to 240/260/280Z/280ZX's c) 84-89 R200's used a 12mm bolt in the ring gear - earlier R200 used a 10mm bolt in the ring gear, so you can not swap Gear Sets with the older R200's


Edited by Miles

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