So I looked at this mod here: http://www.mazspeed.com/msd.htm. Question: Is there any reason I can't use 2 6a's and 4 coils? one box and two coils for leading and one box and two coils for trailing...

 

No; you can do that, but its a lot of $$ to fire the trailing coil(s).

 

You can get away with 1 box for the leading because both the front and rear trigger and fire at the same time. The trailings don't. They are triggered at different times so they need separate boxes to fire at different times. It's more cost effective to simply drop the trailing. Their main purpose is for emission clean up, not performance. Disable the current trailing setup and see if you even notice a performance difference. Bet you can't tell.

 

The easiest thing to for the trailing is nothing leave it stock, It works fine that way, unless you need/want over rev protection and then you don't have to answer endless questions from well meaning people pointing out that your spark plug wires are off. Plus there is no lingering question in the back of your mind: Am I really smarter than some Japanese engineer??????????

 

the trailing CANNOT be fired together, like the leadings can, so if you want to run another MSD on the trailings, you MUST use 1 coil and it MUST go thru the cap.

or you can just run 1 MSD, and run both leading and trailing coils off of it.

 

I think the only way to run one msd box per trailing plug would be to use a standalone computer. But, as mentioned above, it would probably not give you the performance boost you are hoping for.

I think, for the most part, na race cars and turbocharged street and race cars benefit from 2 msd boxes for the leading plugs (one for each leading plug). It's harder to spark as compression goes up, so the turbo guys get big benefits from the mega sparks.

If you have a streetcar, one msd on the leading with stock trailing, in my opinion will be fine.

I have never run 2 boxes on the leading, maybe someone who has can tell us if a mild streetcar will benefit from it...

 

I run Mallory boxes - similar to MSD, but its a Capacitive Discharge system not Multiple Spark. I have one box/coil for leading and one box/coil for trailing and run them all through the stock distributer.

Fuel economy improved noticably, idle improved, and top end power is considerable, especially after a street port. This mod, although pricey, was money very well spent.

I am tempted to put both boxes and coils on the leading and leave the trailing stock with the stock coil, but never found the time to research how to do it. My current setup does have a full rev-limiter which is nice insurance, but since I'm not spraying NOS anymore, I'm not heartbroken if I lose it.

 

Unless technology has changed, I do not think that is possible. You can run only one box for the leading, but the trailing is a separate ignitor.

Think of it as one box per coil on a stock setup.

 

this is how MSD has you hook it up actually. you hook the MSD to the leading ignitor, or magnetic pickup, and then you hook both coils up to the MSD. plug wires don't move.

this gives you zero timing split though.

if you need timing split then you need one MSD on the leading and one on the trailing. and if you do that you might as well run 2 leading coils.

 

is there a big difference between using an after market coil rather than a stock coil? strictly for street use that is.

 

i have two MSD 6al boxes... one for leading one for trailing... full rev limiter too pretty nice

 

Thats got detonation written all over it. I would only do that in a Bridge or PP with overlap. Don't even think of it in a boosted application. Bye-bye seals! Thats a risky way of dong things and couldn't recommend it to others. I'd leave it stock before doing that.

Aside from the sheer age of the coil, the stock ones are fine. High boost, etc, I would go with a hotter one.

 

lol, ive run no split and a turbo... but yeah i'm running NA, where mazda actually WANTS zero split

 

People have had good luck with no-split, but they are the ones that know what they are doing and are squeezing every bit of HP from a motor (most likely with a standalone). I'm not saying it can't be done, but that for someone who isn't experienced - I'd say stay away from it. As far as Mazda intending it.....I'd like to see some evidence of that. If thats the way they wanted it, why don't our cars come that way? Not pointing fingers, just asking since I haven't heard that before.

 

right from the competition manual.... which is @foxed.ca

"5. lgnitiontiming. The timing is set with the drive pulleynotchandthe indicatorpin on the fronl cover; the notches aredenotedas shownin the illus- trationbelow:
The trailing and leading plugs shouldboth be set to fire al 20" BTDC."

why? couple of reasons.

on a high output engine, crossfiring of the spark plugs is very very bad, but if there is no timing split, this basically eliminates the problem, as you can't fire the plug at the wrong time if they fire at the same time anyways.

the second is probably emissions, but even the stock distributor runs split near zero under some conditions, the trailing vacuum advance unit advances more than the leading one does.

not saying zero split is the best way at all, but it can be done

 

So is there any potential problems with just one box for leading and one for trailing? locked dizzy where it normally rests. one box runs off one igniter and the second box off the other igniter.

 

Thats exactly how I run mine - and after more than 18-20 years, she's still running strong without a hickup.

 

If your leading spark is hot enough you really won't need trailing. I did an
HEI ignition using 2 TFI coils (one for each leading plug). I was too cheap to
buy MSD boxes

Anyway, I dropped the trailing ignition because it just wasn't needed anymore
and I could not tell when it was there or not. Also simplified the wiring and got rid
of one HEI and the use of the dizzy cap. I just use the dizzy to get a signal
for the leading HEIs now.

 

nah... all you need is one box w/two coils wired in parrallel and then just run the trailing off the cap and a seperate coil. that is what i did, and i actually ran it without even having a trailing for a while and honestly i could tell no difference with or without. the msd made a difference on easier starting and smoother idle but thats about it. seems like a lot to pay for two 6als and 4 coils for only small benefits....but i mean it would look a lot cooler (more expensive)

 

perfect!

 

I got two used one so i could have a rev limit and still trailing... check out how we mounted mine

 

I tried every configuration with two 6al boxes and I found the best to be 1 box per coil for leading and just run trailing stock through the dizzy or delete it all together. This was for supercharged which i found it ran better under boost with 1 box per coil than 1 box for two coils.
I rev limited the leading and left the trialing stock and it worked fine, the major loss of power was more than enough to let you know to shift.. and your not loading your exhaust with a load of raw gas.

 

Might have to try that.....