Which differential should I use?

  • #1

    Which differential should I use?

    So I have a 1986 auto 2+2 turbo and a 1987 (auto originally, but was swapped to a 5 speed) 2 seater NA parts car and was wondering which differential would be best to use.
    The '86 should have the 3.54:1 and the '87 should have the 3.7:1.

    What are the benefits of either differential, as one should be better acceleration and the other higher top speed (or in most cases lower RPM on the highway)

    I'm just unsure of which should be used. The speed limit around my province is rarely over 90 km/h (56 MPH) so acceleration could be nice, but both are open diffs, and I one wheel peel once the turbo spools if it's slightly wet out, so the higher top end could help with that.
    1986 300ZX factory Turbo 2+2 5 speed swap. 1985 Toyota MR2. Floor boards gone. Good fabrication practice.
  • #2
    Lower number = low rpm for same speed

    88-89na came with 3.9
  • #3
    So if I swapped to the 3.7 I would get better acceleration. Do you know if it's a discernible difference in say 0-60 times? Or should I leave mine and get an LSD later.
    If it's a little wet and I push the pedal about 20% the tire will break loose at about 3k RPM. I've done it quite a few times, and it surprised my dad (who was my passenger as I had a learners license when I bought the car)
    1986 300ZX factory Turbo 2+2 5 speed swap. 1985 Toyota MR2. Floor boards gone. Good fabrication practice.
  • #4
    Load helps spool a turbo, so a lower ratio would get your boost going faster… a higher ratio would give you more torque before boost

    But this all depends on your wheels and tires, if you are going to drive around stock wheels, it won't matter what you do… upgrade those first, then worry about diff ratio
  • #5
    both of that zs you described should have 3.7. 3.54 came 84 - 86 turbo only
    86na2t + holset

    feedback
    viewtopic.php?f=18&t=6114&hilit=andrew+gardner
  • #6
    both of that zs you described should have 3.7. The 3.54 came 84 - 86 turbo only
    86na2t + holset

    feedback
    viewtopic.php?f=18&t=6114&hilit=andrew+gardner
  • #7
    My '86 2+2 is a factory turbo car, not swapped afterwards.
    1986 300ZX factory Turbo 2+2 5 speed swap. 1985 Toyota MR2. Floor boards gone. Good fabrication practice.
  • #8
    if you use the 87's NA trans I'd use the 3.73 to match the trans and speed sensor. thats simplest, and likely the best bet for you. if you go factory LSD, then you can just drop the whole diff in, and nothing changes either.
    Damn dirty angels....these cars!

    Current Daily Driver - 86 Turbo.
    Under the cover - THE BANANA… that needs to be re-energized.
    sigpic
  • #9
    I know the trans is a 71c but I don't know what year it came out of, the parts cars vin says its an auto LOL. So someone's put the 5 speed in it. Its an American car, mines Canadian so I dunno if the speed sensor will work from US analogue to CA digital. I might just leave my diff alone for now and see how it works. If I find the car sluggish ill try throwing the 3.7 into it and see how that works out.
    1986 300ZX factory Turbo 2+2 5 speed swap. 1985 Toyota MR2. Floor boards gone. Good fabrication practice.
  • #10
    I have the 3.54 and love the cruising speeds. I can feel the slight difference between it and my other 3.9; no one else can. That said I rather have the lower gears. Once I get my target 275-300whp it will not matter much. (Cruising at 2.6k rpm @ 55 with the 3.9 is silliness). As an added point - there will always be someone faster, so choose what is most functional for your car's common used purpose.