MSD 6A on trailing, why not?
 

The other day I bought two MSD 6A boxes and planned on using both of them till I read an article that said not to because the box on the trailing ignition would ignite the incoming mixture from the next stroke, and would break apex seals. Is this correct? I called MazdaTrix, and they helped me none. So then I called Racing Beat, they told me to call MazdaTrix. So here I am, hopefully you guys can help.
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Ha ha.... There are guys that run 4 msd boxes, one for every plug.

The spark coming from the trailing is very weak, you car will even run without trailing wires hooked up.

It's your choice, You could run one on leading ignition and one trailing or One box for each leading spark plug.

I currently am looking to get a second msd box aswell.

How would you run two boxes on the leading, when there is only one pick-up for the leading in the distributor?

I'd leave trailing completely and utterly stock. Well, I'd move the wires to the leading part of the cap and maybe adjust the vacuum dude for a better split, but that's as far as I'd go.

Most folks here know I wouldn't even use an MSD on leading. I have one here, a 6AL sitting in a box, waiting for a piston engine because it really wasn't that great on a rotary. I've compared it to DLIDFIS and the latter is the only way to go in my subjective opinion. Well, there's also 2GCDFIS if you have the parts and desire to use it instead. I'm biased toward DLIDFIS and I've had the most experience and success with it.

Do some searches before committing all your money to those clunky red boxes. :D Man, that could get expensive for so little gain.

Yeah let me tell you, I've already bought the two boxes and two additional Jacobs Ultra Coils. I think I'm going to return these and get my money back. I would use them both, but I dont want to destroy my engine.

You could return them and go buy a new or used 2nd Gen leading coil. Its really easy, and gives you more than enough spark. I run 2GDFIS and I love it, I have no desire or need to run anything with more output.

And the 2GDFIS will save you a TON of money over those MSD boxes, I am pretty sure that DLIDFIS is also a cheaper route.

Thank for the Info guys!

If all you had was 1st gen parts, DLIDFIS is the cheapest because it only requires one more ignitor and coil. On the other hand, if you have easy access to a 2nd gen coil, 2GCDFIS could be cheaper because it technically only requires one ignitor. It's still a good idea to upgrade the ignitor from a J-109 to a GM HEI though. The HEI is only $17.00 brand new from my local Autozone. Part number DR100

I don't know about retaining the ballast resistor in the circuit. I know the stock 2nd gen ignitor needs it because the coil has low primary resistance. Maybe the HEI can handle it? I know it goes into current limiting mode at 5 or 6 amps where the J-109 can only go up to 3 amps. I'm not sure about the stock 2nd gen ignitor, and whether current limiting is affected by the ballast resistor.

For a real 'shocker' pardon the pun, I'm going with dual 2nd gen leading coils and GM HEI ignitors on the 4 rotor for ultra ease of installation. Only two coils for four spark plugs. :D There will be no problem fitting them in there. Less likely with four seperate 1st gen Diamond or similar coils. I suppose I could keep two in the stock location and mount the other two on the strut tower. Of course that would require four ignitors and a nightmare of wiring. Nah, dual 2GCDFIS is best.