Jump to content
HybridZ

3.90 diff


Recommended Posts

I have a 1974 260z with a Chevy 327 and bigger cams.   I'm thinking about putting in a 3.90 diff off of a 240sx.  Are the RPMs going to be too high on the freeway?  Anyone else with that setup?Thanks in advance!

Link to comment
Share on other sites

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. 

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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

 

http://www.zhome.com/ZCMnL/tech/GearRatios.html

 

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
Link to comment
Share on other sites

On 7/9/2019 at 1:55 PM, Miles said:

How do you use the car?  Daily driver?  Race car? 

 

 

I'm back!! I use the car strictly as a race car. I used to drive it to events every once and awhile, but I've put a different transmission in it since then. 

 

On 7/9/2019 at 3:42 PM, Neverdone said:

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.

It depends what variety of 240sx you're talking about. R200 parts are damn near lego status. Yes the gears are housing specific, BUT the open diff s13 has the same axle spline count and length as the 240/280z R200. So you just need to make a new driveshaft and front diff mount. The rear cover will also transfer from a 280z R200 to a s13/s14 R200. 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...