I have an '85 12A motor that I have setup to fire both leading plugs at the same time. I am direct firing them via a MSD 6A ignition box to 2 MSD Blaster coils connected directly to the plugs (not firing back through the distributer). This setup is running FANTASTIC!!


Currently I do not have my trailing plugs hooked up or firing.


My questions are:


1. If I use my trailing plugs, how much additional power should I see? 5%? 10%? or more??


2. Can I fire the trailing plugs at the exact same time as the leading plugs?


3. If I can/should fire the top plugs at the same time as the lower, can I just switch the T1 and T2 wires on the distributer cap to plug into the L1 and L2 positions respectively on the distributer cap and switch the coil wire on the distributer cap from T to L?? Remember, currently I am not using L1 and L2 positions on the distributer cap as I am direct firing from the MSD ignition box and not through the distributer for my lower plugs.


As always, you guys have helped me learn a great deal about rotary motors so thank you in advance. I am more knowledgeable in straight 4's, and 6's, and v6's and v8's but I am totally digging this rotary. Fun... fun... fun.


thanks!
Bill

 

1. i seriously doubt there would be any increase in power.

2. no, absolutely not.

3. see #2.

 

Actually, number 2 has been done by novice tuners repeatedly in the 2nd Gen megasquirt scene, and I haven't read it causing issues with NA applications yet. I'd also note that it had no benefit either.

My 12a ran that way for over 2 years without my knowledge after I botched an MSD install.

 

I ran my ignition leading only for a few years and finally switched to firing L and T. Heres my take:

1. Very little power, if any, added at all. Slightly smoother idle and cleans up the exhaust smell
a bit.

2. Yes, thats called zero split but you can't fire both trailing using the same trigger as it would
lead to damaging misfires on the other trailing plug. You would have to use a dizzy or a
computer to do this correctly so that each trailing plug fires independently. Not clear zero split
will buy you much, except igniting the flame front in 2 places at once. Shouldn't hurt anything.

3. Yes you can do that it provides a shorter more direct current path for the trailing ignition.
I do that in my setup now and many others do it as well.

You will need to setup the trailing ignitor and a coil to fire the trailing plugs through the dizzy.
Not sure you are intending that, seems like you want to use the MSD to fire everything at
once. Might work if the MSD can handle it. So I'm a bit confused on what you intend.

 

1. depends on the port, in a stock port its like 5%, on a P port its like 50%, not quite sure why.

2. we need to define that a little. you cannot fire the trailing plugs at the same time like you can with the leading. with the leading one plug is on a compression stroke, and one is on the exhaust stroke like a piston engine. with the trailing, one plug is on the intake stroke... you can however run the same (or nearly) the same spark timing. again on a stock port you wont see much difference. the FC runs close to zero timing split (# of degrees between leading and trailing) at light loads, and the Rx8 actually fires the trailing first at idle. the race engines just had 1 pickup in the distributor, and two CDI boxes, with 2 coils, and thus ran the same spark timing, leading and trailing, more for reliability, as you can't have crossfire if you fire everything at once.

3. ive never run the trailing through the leading side of the cap, but everyone else has, works for them.

 

See if this drawing helps. Essentially:

1. Leading igniter pickup on the front of the distributer signals the MSD ignition box.

2. The MSD box fires all 3 coils at the same time.

3. One of the coils is connected directly to L1 plug.

4. One of the coils is connected directly to L2 plug.

Numbers 1 through 4 above works fantastic.

Below is what I'm wondering if it will work:

5. 3rd coil is connected to the L input on the distributer.

6. L1 port on distributer cap is connected to T1 plug.

7. L2 port on distributer cap is connected to T2 plug.

What da ya think??