So after looking at all the various DFIS mods ( DLIDFIS, 2GDFIS, MSD6a etc) where they are basically firing the lead plugs twice during each combustion phase, the so called "wasted spark" ignition, it dawned on me that I really wouldn't need the trailing ignition at all. I know I've heard some folks run competition cars without the trailing plugs and the holes are plugged.

If I run a DFIS system, then shouldn't I be able to drop the trailing ignition all together ? I can't think of a good reason to keep it, it will be doing very little at this point and its just one more item to maintain.

I'm about to switch over to the 2GDFIS to see how well it works and I'm thinking of dropping the trailing ignition and see if I notice its affects. What I'm thinking of doing is run with the trailing after I install the 2GDFIS for about 2 weeks. Then drop the trailing and run it that way for another 2 weeks. This isn't my daily driver but I can usually drive it enough over 2 weeks to go through more than one tank of gas. I'm betting that I won't notice the difference.

 

Trailling is mainly for emissions. With a so called "wasted spark" direct fire ignition system, trailing becomes even less important. It cannot add very much power to the overal power output of your enginer because it physically fires through a very small hole. Ever seen those spark plug non-foulers at your local auto parts store? The tiny hole in those is about the same size as in the trailing holes in your rotor housings. The reason for the smal size is to prevent compression loss as the apex seal passes over it.

Dyno tests have shown that runs without trailing vs with trailing show that the HP difference is within the margin of error of the dyno software. Trailing isn't worth the effort to upgrade in NA (naturally aspirated) in my opinion. The only time it might help boost power is if you're running lots of boost, but then I'm pretty sure you'd also have fuel injection and an engine management computer controlling timing/ignition as well. Ask RETed if you're curious and plan on running a big turbo with lots of boost and all that. Otherwise, leave trailing stock and don't worry about it.

By the way, there is a reason the tach is hooked to the trailing ignition. Trailing is so weak that you'd never know it died without a visible reminder staring you in the face every time you drive (and what person driving a rotary doesn't look at the tach on a regular basis?). When upgrading your ignition system, I recommend moving the trailing plug wires from the trailing part of the cap to the leading part to take advantage of the carbon button and one less gap to jump. That's it. That's all the upgrading trailing ever needs. If your trailing ignitor or coil ever goes out, you can replace those parts at your leisure.

 

Ah, yes the tach input based off of the trailing. Thats the only good reason to keep it I guess or at least keep the tariling igniter. The tach won't operate from the any other sigtnal will it ?

No boost here, just a N/A 12A with Dellorto carb and Rotary Engineering exhaust. Thanks for the response.

 

What if you physically modified the trailing plug hole so that it matched the leading? Doing this, of course, while running with upgraded FC ign components.
I wonder what effect that would have.. I bet you would notice something then, though how much...
I'm thinking by having a stronger trailing spark, it could be tuned to speed up the flame front somehow.

Was there a reason that the trailing hole is smaller? Also, do they still do this on later FD engines and the renesis? If so, it could be a good reason, and enough not to mess with it..

Lastly, assuming you COULD have equal spark at trailing and leading. If you decided to run trailing only, how much advance, in an of itself, would that provide?

 

The reason for the small size of the trailing holes is to prevent compression loss as the apex seal passes over it. Enlarging the holes will allow tons of compression to leak around the apex seal as it passes over the hole.

 

Actually, trailing INCREASES NOx and HC emissions, strangely enough... It's there for power and economy.

At least according to this document:

http://smrmicro.com/re-ky.pdf

 

but dont u still have to adjust your trailing even when changing to 2gdfis

 

I'm not even running trailing on my 20B. It was a trade off between late leading or leading and trailing at the exact same time (no split). I chose the former. Everybody else chooses the latter. My 20B certainly sounds cool with the later firing leading spark; kinda similar to the difference heard when going to a direct fire ignition system with the so called "wasted sparks" on a 2 rotor. That is to say the 20B still sounds like a 20B and all that... It's just a bit different than everybody elses, and that makes it cool.