People using MSD's or CDI's on the Leading Only - Please Read!
 

Hello all,

This thread is to get peoples feedback and theories behind using a single MSD or any CDI on the Leading ignition coils only. The first question i have for you is how do you have the ignition setup to, mainly the Spark Output Type? do you have it set to constant charge or constant duty, also, the spark edge, since MSD's require a Rising trigger edge, and the stock mazda igniters use a falling edge and constant charge, i wanted to know how do you work around this? Or do you configure this just as you would if it was only stock coils/igniters?

Also, when you "zero in" your timing what kind of trigger angle and tooth offset values do you end up with?

I really want to understand the reasoning behind using just one form of spark amplification on the Leading plugs alone.

Thank you.

The reason for using it on the leading mainly is because on a rotary the leading handles the bulk of the load and the trailing is really to ignite the left over fuel due to the long combustion chamber a rotary has. The trailing is basically a clean up plug. That's a simple explaination. There are other factors involved depending on application where the use of a CDIi on the trailing can be beneficial. If using it on the leading ignition only then the least complicated setup would be to wire it between the igniter and the coils. The ignition setup would remain the same as stock. Now if you're using MSD's on all the ignition outputs then the igniter can be removed from the setup if you choose too. The ignition setup would have to be changed to suit triggering the MSD's directly meaning rising signal/constant duty. The 'rising' edge trigger is what MSD requires period. As for 'constant charge' vs 'duty' with MSD's the analog boxes require ''constant duty' and the digital boxes can work either way although it's application specific because as of late since MSD went with the new processor it seems some prefer the 'constant charge' method. Your best bet would be to start with the 'constant duty' method and proceed form there. I've more consistant results with the 'constant duty' method anyway.

Yes, If using a single MSD Unit on the Leading Coil only, then it's wired in between the stock ignitor and the coil. The settings are the exact same as stock, as the MSD unit is acting as an amplifier.

If its used on more than one coil, then settings/wiring do change as the MSD unit now becomes the ignitor.

Very good post and info, btw!

Then how is the wiring arranged between the Haltech and the MSD's if you are using three of them in place of the igniters? Does the spark mode change? Do the trigger settings change?

Trigger will always remain the same, (engine specific), but the output will have to be set up for the MSDs to work properly.

Comitatus has a valid point, in the single leading MSD option, the MSD HAS to be wired between the stock ignition module and the coil, meaning the haltech will be firing the igniter like it normally does, and the igniter sends its signal to the MSD, then the MSD sends its capacitive discharge to the coil. If you hook up the MSD before the Igniter you might fry it.

Thanks Cris for that helpful bit of info. Personally, i would like to know if you get any sort of differences in the timing end results by having the MSD on the leading only. Since edges play a part in the exact moment the timing occurs, does anybody have anything to add on this?