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
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Mazda Engine Swap
- Thread starter robertf
- Start date
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
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.
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.
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.
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?
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?
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.
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.
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.
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.
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.
Hi Dan, the rockauto web site shows 13/16 as bore size and 1971/72 Doge colt as OE equipment.
