Which coil MSD? Leading or trailing?
 

I apologize if this has been posted already.

Which set of plugs derives the best benefit of an MSD6a? Leading or trailing or both?

I'm using the stock plugs in an '84 GSL-SE using the same plug for both, BR8EQ-14. Are there better plugs out there? My climate is mostly above 50 degrees but I'd say it averages around 75-90 F. degrees year round although it can get colder during the winter.

Thank you,

Leading. Trailing provides little to no power gains. Mostly there for emissions purposes.

For street use, FC plugs are fine and they are pocket items at junkyards lol

Emissions? When my trailing coil went out my motor wouldn't even start! I would say thats performance oriented

Wrong! The trailing has no affect if your leading ignition is working well. You won't
even notice it missing. If your seeing issues with the trailing disconnected, start
looking at your leading ignition carefully, as it must be very weak for the trailing to
be needed for startup. BTW, you can run on trailing alone and some folks do without
realizing it when the leading fails, they just notice the car is weaker and runs "funny" :)

Whiche segues into another question
 

Which segues into another question. What is the order of ignition. Which fires first, and when does the other kick in unless they both fire all the time? I don't mean whether the leading fires first in the firing order, it's got to be called the leading coil for something. The ignition system is pretty simple but is there any time when either one doesn't fire by design?

I had the same problem as the poster above, I removed my leading coil and it ran terribly. I removed the trailing coil and it died. I've got a bunch of ignitors if that is the problem.
Thank you,

Leading fires first, trailing fires after to burn off any of the mixture that didn't burn from the first firing.

The leading fires, um, first and then the trailing follows as the combustion chamber
comes around a bit more. Trailing is there to help burn more completely the mixture
for emissions purposes. In a boosted application I beleive trailing is needed to keep
things smooth but I'm no boosting expert. The trailing can fire randomly.
Depends on what year your car is. The SA models turn off trailing on decel and some
other times to promote the burning of carbons in the heat exchanger. Later models
kill the fuel pump and tach if the trailing fails. All depends on year and model you have.
The GSL-SEs may have yet another subtle difference, but I'm not sure on that.

You got it right bro. I cant explain it any better. You nailed it

That's not what I meant
 

That's not what I meant which is why I wrote this:hah:


Let me rephrase it so it makes more sense. Do both coils fire all the time or are there times when one system or the other isn't running for some reason. Since the ignition schematic is pretty simple, I don't see a way to do it.

An engine runs fine without trailing.

The SA cars had semi-firing trailing. At times the thermal reactor needed a richer mixture so Mazda would turn off the trailing ignition. This is why they had the tach connected to the leading ignition.

Or maybe your car is an 84-85 model which had a fuel pump relay connected to trailing. When something in the trailing ignition stops working, Mazda forced you to deal with it. So it's possible it didn't start because it wanted fuel.

Take-7 hangs his head in shame...

No shame in learning something.