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Thread: E30 12a Rotary Swap

  1. #1
    Join Date
    Oct 2018
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    E30 12a Rotary Swap

    Hello,
    We are currently in the starting phase of swapping an 86 325es to a 12a rotary. Is there anyone here who has done the swap before?
    In addition we will have both the mazda smoothcase 5 speed and a getrag 260. The mazda trans comes with the engine. We think it would be easier to use the mazda trans but we have heard that the mazda is far weaker than the getrag. This won't be a super high up build, we would be happy with ~250hp.
    We have a machinist so making adapters and the sort is not that big of a deal. Any insight would be greatly appreciated.

  2. #2
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    Why 12A?

    The Getrag 260 would make the driveshaft part super easy. I'm sure the Mazda trans would handle that kind of power, especially since a rotary makes it up high, not from high torque. Are you planning to rev to 10k to get that kind of power or going with something crazy like a peripheral or bridge port?

  3. #3
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    hiss by my window
    Not sure if it would be easier to adapt the Getrag to the Mazda or fab a driveshaft to use the Mazda gearbox. Probably the latter.
    FWIW I worked for Mazda when these were current and owned a few of them too. I beat the living snot out of them all and of all the stuff I did break, gearboxes wasn't one of them.
    Interesting swap but me thinks this engine is poorly suited to the heavier E30.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  4. #4
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    Quote Originally Posted by ross1 View Post
    Not sure if it would be easier to adapt the Getrag to the Mazda or fab a driveshaft to use the Mazda gearbox. Probably the latter.
    FWIW I worked for Mazda when these were current and owned a few of them too. I beat the living snot out of them all and of all the stuff I did break, gearboxes wasn't one of them.
    Interesting swap but me thinks this engine is poorly suited to the heavier E30.
    Agree. I've owned 12A and 13B cars, NA and turbo, would never put a 12A in an E30. 13B turbo on the other hand.

  5. #5
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    The reason for a 12a is that there what we have. We were able to get a 12a for fairly cheap. It will be stock port at least initially. Most likely it will get a Subaru or saab turbo before too long and a p port. It won't be 250 out the gate obviously.

    We too think it would be easier to adapt the mazda than the getrag. Its pretty much decided that mazda is the way to go.
    With any luck the m20 will be out in about a week or so.

  6. #6
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    Me thinks it easier and cheaper to get 250 out of the M20 and you won't need to rev the snot out of it to get going.
    A "convenient" swap isn't always a good idea.
    That is all.
    Last edited by ross1; 10-22-2018 at 08:56 AM.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  7. #7
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    M20 is out.
    Its not really about a convenient swap. The convenient thing would be to fix the m20. We didn't want to that, we wanted to do something different. This is the result.

  8. #8
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    Peripheral port on a street car is pretty rough. You could grab a 5 speed out of a 13b FC, those always seem floating around on craigslist. Making a custom trans adapter is always a pain.

  9. #9
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    Quote Originally Posted by Cryosignal View Post
    Peripheral port on a street car is pretty rough. You could grab a 5 speed out of a 13b FC, those always seem floating around on craigslist. Making a custom trans adapter is always a pain.
    Even a bridge port is a bit much, especially with how weak it gets on the bridge... An aggressive street port is about as far as I'd go. I've had some pretty gnarly 13B's, including an NA street ported 4 port running a Holley 750cfm carb in a REPU, rough guestimate on that one was 200hp.

  10. #10
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    Adapting the trans won't be a problem. It'll be using a miata na trans. Calling it a street car would be a tad generous. It won't be all out race car but certainly not a reasonable street car.

  11. #11
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    No one has put a 12a in anything but a dumpster. It’s barely strong enough to move a 2,000lb rx3 let alone a 3,000lb BMW. None of this makes any sense.

  12. #12
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    Hola Friends,

    Not too many hardcore purists on here, just dont put chromes on it..


    Can't add much re: rotary conversion, but if you want to stick with a e30 diff, I have a really good ratio one that will suit perfectly for free, just if you want to pay the freight up to Auckland
    kissanime.
    Last edited by 74San; 11-02-2018 at 07:32 AM.

  13. #13
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    Hello, here's an update. The transmission rebuild took longer than expected but its done now. The pain of sourcing a miata/rx7 slip yoke will be coming to a close soon. The car is mostly ready for test fitting and the 12a has been stripped to make the process easier as well as remove the emissions garbage.

    The current agenda is to mount the motor to the transmission and test fit it into the car. Then engine and transmission mounts will need to be made. At some we will need to decide between retaining the stock carburetor setup (obviously with a different carburetor than stock) or go efi.

  14. #14
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    Quote Originally Posted by Delan Speed View Post
    Hello, here's an update. The transmission rebuild took longer than expected but its done now. The pain of sourcing a miata/rx7 slip yoke will be coming to a close soon. The car is mostly ready for test fitting and the 12a has been stripped to make the process easier as well as remove the emissions garbage.

    The current agenda is to mount the motor to the transmission and test fit it into the car. Then engine and transmission mounts will need to be made. At some we will need to decide between retaining the stock carburetor setup (obviously with a different carburetor than stock) or go efi.
    Having run a carb'd 13B... You don't want a carburetor. Go EFI, so you don't have any fuel starvation issues in turns. I had the Racing Beat manifold and a Holley 650CFM carb.

  15. #15
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    Or just throw this piece of junk in a dumpster and get literally anything else.

  16. #16
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    Ah yes. The long awaited update is finally here. Sorry it took so long. The motor and transmission are in the car and surprisingly the shifter lines up perfectly. The yoke issue is sorted and a custom one piece driveshaft is just a dimension away from being made. The motor and transmission mounts are in the process of being made. The only real gripe is that the oil cooler on the motor is really really close to the brake booster. Pics are on our Instagram @delanspeed if you want to take a look.

  17. #17
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    1997 328 convertible
    Did you ever finish this? For whatever reason I have got it in my head that I really need a Cosmo 13B-RE turbo in an E30

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