Gearbox options for replacing 240z autobox with RX8 6 speed?? | The Z Club of Great Britain
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Gearbox options for replacing 240z autobox with RX8 6 speed??

Discussion in 'S30 (240Z,260Z,280Z) Drivetrain' started by hallie, Jul 14, 2019.

  1. hallie

    hallie Active Forum User

    I have a USA 1971 240z fitted with a autobox. It has the later L28 engine and I would like to convert the car to manual.

    I know that there are 4 and 5 speed boxes available occasionally secondhand but I was wondering if anyone had used the 6 speed gearbox out of a Mazda RX8?

    I already have one from a very low mileage car that isnt being used at the moment.

    I assume that I would need an adaptor plate plus special flywheel combination.

    Does anyone know if this has been done already? or of a reason why I cant do it? (perhaps the box isnt strong enough?)

    Thanks for any help

    Martin
     
  2. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    I would think the box is strong enough. Will it be too big for the transmission tunnel?

    Ratios might be an issue with your diff.
     
  3. franky

    franky
    Z Club Member

    I’ve look at this as an option. Adapter place is fairly easy to sort, the box is nice and narrow, Haven’t got around to measuring up an rx8 box though.

    Can you pm me measurements and dimensions?
     
  4. hallie

    hallie Active Forum User

    I dont think its that large a box. I need to get it down from where its stored.

    I was planning on changing the rear diff to suit with a Subaru lsd unit
     
  5. hallie

    hallie Active Forum User

    Will post when I get the box out to measure.

    Where have you seen an adaptor plate?
     
  6. franky

    franky
    Z Club Member

    a 6 speed rx8 box, with a nice 4.44 gives a lovely close ratio with sensible overdrive.

    I've had the design mocked up to make a 'batch' if need's be.
     
  7. hallie

    hallie Active Forum User

    6-speed Manual:

    1st 3.760; 2nd 2.269; 3rd 1.645; 4th 1.187; 5th 1.000; 6th 0.843; Final Drive 4.440

    Does that look right?

    What ratio would the rear diff be on my US spec auto 240z. Not that I really want to keep it as its not a lsd.

    I do have a R160 subaru 4.44 lsd and possibly a subaru r160 4.1 lsd
     
  8. chrisvega

    chrisvega
    Z Club Member

    240Z Auto diff ratio is 3.545
     
    SacCyclone and hallie like this.
  9. datsfun

    datsfun
    Z Club Member

    A friend has done this conversion for his CA18DET and plans to run 400+ bhp.

    In his words, it's a strong box and very well priced in 2nd hand market.
     
  10. SeanDezart

    SeanDezart
    Z Club Member
    Official Trader

    Following.
     
  11. atomman

    atomman
    Z Club Member

    I have looked at the Rx8 box and it looks a good option because of price and availability, If an adapter plate an be easily made and the input/clutch can be sorted

    I'm currently running a Subaru 4.1 R160 (clutch) LSD on my car ,

    What 'type' LSD's have you got ?

    Also Tyre size can make a difference on the final ratio to, This calculator came in handy for me http://westfield-world.com/gtc.html
     
    hallie likes this.
  12. johnymd

    johnymd
    Z Club Member

    The guy in the workshop next to me is using the rx8 box in his 105e Anglia. He has adapted it to fit the v8 Yamaha R1 engine he's built. He chose the box as it was cheap and best suited to his low torque hi power revy engine. I keep looking at fitting it into a zed. He has a few so I may pop next door and borrow one to do a mokup.
     
    hallie, atomman and Chappers like this.
  13. hallie

    hallie Active Forum User

    The 4.1 R160 Subaru diff I have is a viscous LSD from a 1991 JDM Legacy turbo
     
  14. SeanDezart

    SeanDezart
    Z Club Member
    Official Trader

    I would doubt the resistance of an R160 in a Z.
     
  15. atomman

    atomman
    Z Club Member

    Have you got the Drive shafts ? they are different to the other types and not as easy to make work, the Suretrac and clutch type are much easier.

    Have you got any experience/know anyone using one ?
     
  16. SeanDezart

    SeanDezart
    Z Club Member
    Official Trader

    No, I confess to not having taken the risk. Having moved down from an R200 to an R180, I'm crossing my fingers that the 180 will cope.

    The R160 is also designed to cope with approximately half the engine power - no ?
     
  17. atomman

    atomman
    Z Club Member

    I've got a Type RA 160 Clutch LSD fitted in mine and the bored out L28 is kicking out over 200bhp and I've had no problems.

    If you look at the Ozzie forums they have been using them for years.
     
  18. franky

    franky
    Z Club Member

    Like most times, you're completely right. its the spider gears in none-lsd's that fail. there's 400+bhp with torque being put through r160's.
     
    atomman likes this.
  19. SeanDezart

    SeanDezart
    Z Club Member
    Official Trader

    Do they share the same output splines for the same half-shafts as those for the R180s ? What is the difference in weight anyone ?
     
  20. hallie

    hallie Active Forum User

    I have subaru shafts to go with the diff but nothing to suit the 240z

    [​IMG]

    It has stub shafts protruding from the diff
     
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