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Mazda Engine Swap

Discussion in 'Modified Alpine' started by robertf, May 21, 2008.

  1. robertf

    robertf Donation Time

    I just looked at page one and wow, its been a while.

    The nova in that picture is in the middle of a restoration and the disco that I brought the engine home in has had everything replaced except for the transmission and transfercase


  2. Gitnrusty

    Gitnrusty Donation Time

    Bought my Dodge colt mc from Rockauto. It arrived in a NAPA box! (NAPA had shown it as obsolete)
    Took it into NAPA to buy brake lines and an adapter. The counterman took one look, walked to the cabinet of brass fittings and came back with one that screwed into the mc and the common brake line I was buying screwed into it.
    Love those old time parts guys (we don't need no stinking computer).
    I think the NAPA # was 641-5026 $3.66.
    Trial fitted to the car and seems to be OK. Not as pretty as the Nissan cyl. tho.
  3. Cactusmasher

    Cactusmasher Donation Time

    Mazda swap

    Just an FYI for others seeking odd adapters for fluid lines, especially crossing MM with SAE threads......try a local motorcycle shop. I had a problem mating similar threads and needed an adapter. Tried all over town and several places suggested a motorcycle repair shop. I went there and showed the counter guy what I was trying to hook up. He walked into the parts area and came back almost immediately, handing me a fitting and said " Here's what you need ". For a couple of bucks it solved my problem. Just a thought in case someone needs some help in that area.
  4. DanR

    DanR Diamond Level Sponsor

    Hi Guys, What is the bore size and is there any specific year for the Colt Cylinder?
  5. robertf

    robertf Donation Time

    While I'm waiting on clutch and brake parts I'm starting on the little things like gauges

    The oil pressure was easy, a 3/16 compression fitting to 1/8NPT and some new nylon hose took care of that. The coolant reroute that I did to the Miata engine provided a blanking plate for the OEM temp sensor

    The tach is the problem. The Miata ignition module provides a square wave tach output.

    I think if I remove the transformer from the tach and replace it with a PNP transistor it should drop the voltage when high to trigger the factory tach components, but Ive forgotton what little I ever knew about electrical engineering. I know some of you have experience with this. Any recommendations on resistance values, maybe voltage spike supression that I left of, or will this even work?


  6. RootesRacer

    RootesRacer Donation Time

    If the Miata uses a 4 post coil pack, just put the current feed to the coil through the tachs current transformer (with polarity change if needed).

    The coil will put impulses on the tach JUST like if you had points and a single coil.

    You may need to change the number of turns to the impulse transformer (1 to 4 turns) till you get a functional signal, but likley 1 turn is all you need.

    This works on my distributorless setup on my alpine and the stock tach.
  7. robertf

    robertf Donation Time

    Well that would be an easy way to do it

    Just for the sake of investigating an alternative am I right in thinking that the pulse width of the transistor should be less than the coil saturation time? I think I'd need a one shot to keep the smiths rc circuit happy.

    At 60 degrees dwell / 720 at 7000 Rpms I'm figuring about 3ms is the smallest pulse width if the coil isn't fully saturated at that speed. I forget how to calculate coil saturation time.
  8. RootesRacer

    RootesRacer Donation Time

    You are way over thinking it.
    The current pulse occurs at the instant the ignition transistors open. The dwell time doesnt factor much into anything. The coil current does.

    If you do modify the smiths tach circuit (which makes no sense to me at all), you would want to trigger Q1 with a very short PW signal (like the transformer does).
    The circuit works by having the transformer provide bias to Q1 with the current impulse. This triggers Q2 through the RC network forming a one shot flip flop (monostable?). Q2 then holds off Q1 till the RC has charged.
    This works becuase the transformer becomes essentially a very low value resistor when there is no change in coil current.
    Put a transistor in the mix and you will need to make the transistor on all the time except for a very brief interval (200micro seconds or so) as the coil dumps to the secondary.

    You will need a pretty sophisticated circuit to keep the smiths tach otherwise happy and in the end, using it as it was designed works and is dirt simple.

    The only reason I would entertain modifying the tach would be if you were using an MSD ignition and then I would gut the smiths circuitry and make my own digital one shot circuit to drive the movement.
  9. Gitnrusty

    Gitnrusty Donation Time

    Hi Dan, the rockauto web site shows 13/16 as bore size and 1971/72 Doge colt as OE equipment.
  10. robertf

    robertf Donation Time

    There are 2 master cylinders, steel and aluminum. The aluminum is 11/16 and the steel is 13/16. I think the difference is power or unassisted brakes

    Mine showed up today

  11. robertf

    robertf Donation Time

    Clutch and brakes plumbed.

    Shifter completed, had to shorted the linkage 3/32.

    So close. Picking up the modified radiator tomorrow

  12. Alpine66

    Alpine66 Donation Time

    Modified radiator as in reworked OEM? Or custom? If custom what did you get?
  13. robertf

    robertf Donation Time

    Reworked stock radiator
  14. Alpine66

    Alpine66 Donation Time

    Assuming you kept the same position and size on the inlet/outlet? If not what did it cost?

    Pricing I got here to recore and reposition was high enough I'll just get a custom. Unless I can find something that fits; which so far has been a waste of time.
  15. robertf

    robertf Donation Time

    Bills radiator in plano tx. Both inlets had to be swapped. It was 140

    I had the same shop do a 2 to 3 core rebuild on a tdi defender radiator and that was 700. I'd expect an alpine to be slightly less than that
  16. Alpine66

    Alpine66 Donation Time

    Yes, I can get a custom for $500 iirc so that's likely the way I'll go. I've checked a lot of radiator sizes and so far haven't found one that fits well .
    Especially since I'm needing passenger inlet and driver out.
  17. robertf

    robertf Donation Time

    Loom and coolant lines almost done. I'm now running in to all the problems I said I'd deal with later like broken studs at the back of the engine that take 3 hours to remove


  18. Bill Blue

    Bill Blue Platinum Level Sponsor

    Any ideas on the air filter? That front mounted TB does not leave much room.

  19. robertf

    robertf Donation Time

  20. Bill Blue

    Bill Blue Platinum Level Sponsor

    Okay, that'l work, I think. I immediately started to wonder how it will perform while wet. Looks like Dallas gets about 40" of rain a year. Perhaps a simple shield?


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