interested in knowing who out there runs only leading ignition only.
 

kind of a poll, since i don't see it talked about too much, also what were your power results on leading only.

You should also ask wasted spark or not.

i've done it before, didn't have a dyno at the time to see power gains or lost but it worked good.

i would assume waste spark, since it seems to give the best results in these engines but good point.


any more details like boost level, any dynos at all? power felt similar? plug fouling issues?

i'm trying to gather pros and cons of even using trailing ignition in some setups. i have used leading only before and the difference was hardly noticeable but not so far in any higher end builds. knowing that trailing spark can be detrimental and even quite costly at times. a fouling leading circuit may not even be noticed but the engine will surely notice it.

some engines fail due to mysterious circumstances, it would be nice to have the info on hand from those who have successfully used it.

The reason I brought it up is because at high RPM there's less time to charge the coils so single spark sometimes can work better, but you're right most of the time wasted spark works better. Like 99% of the time in my experience.

i have no experimental data, but i would hypothesize that trailing ignition doesnt make any difference to peak power. if you are running any less than 15 deg advanced, with 15 split at max power, the trailing plugs are firing on the down-stroke, which shouldnt affect power at all.

but I think trailing ignition does makes a big difference under light load, where you run closer to zero split. try cruising at constant speed and vary split from 15, stepping down to zero, you can feel a it has more power the closer to zero split you get.

I would say the effect of trailing ignition is like a linear curve from max power down to light load

Some of us now even run large negative split for idle and very light load as it also runs smoother and can run leaner.

:icon_tup: I've been doing this for awhile now with great success.

When I did it we were only running 15 psi, it feel like we lost power, we also never had any fouling issues. We blew the motor because of a faulty fuel pump. I honestly couldn't tell the difference even at low rpm. I'm gonna tune my car in a few days, I haven't tried this in a long time but just for r&d I'll disconnect the trailing plugs and see the difference as the car was tuned at about 14 psi before.

I'm bring this back too see if there has been a change of opinion. I ran no trailing for 3 years on my 6 port NA half bridge, wasted spark, msd 6a, 2 blaster coils direct fire, haltech e8. Engine ran great, put new plugs in every spring but I wouldn't say it needed it.

I'm installing a turbo and a new haltech elite and thinking of keeping it leading only unless some info turned up that would change my mind....

Also did any of you use a block off for the trailing plug hole? A o2 sensor plug is the same size and thread but not sure if it would be a bad idea due to sealing the threads.

Not turbo, but none of my bridge ported engines liked having no trailing. They did not idle or drive at low load at all.

It is sensitive enough that I can feel it on the highway when the terminals in the distributor (for trailing only) are dirty. Lots of little light-load misfires that go away with more throttle. Pull off the road, scrape the terminals with a small screwdriver, and it's fine again. The corrosion seemed to get worse/happen more quickly when high RPM would be used - I'd drive down to a rallycross just fine, and it would run like crap on the way home until I'd clean the distributor. Drilling a pair of 1/2" holes in the cap helped this dramatically, and I wish I could remember why I tried it.

(Yes, I know the fix is direct fire. Not ready to do that yet)

No reason to not run trailing. Properly calibrated trailing timing helps tremendously at low loads.

as far as load lows anyone wanna share numbers? i run what i thought was the factory 15 split in vacuum.

Anyone care to share an example of what negative split ignition curve for idle and light load looks like. Would like to try it. Mainly for fuel economy.

I'm curious as well. I've been running zero split since forever and the main reason i want to go to direct fire is so i can play with negative split, but this is uncharted territory for me.

Curious, helps in what way? HP? Fuel economy? Throttle response?

I didn't notice a difference when I removed mine. One possible reason could be the direct fire with MSD, please correct me if I'm wrong but I recall that MSD continues to fire the spark for 20 degrees of rotation, besides the location of the trailing plug I think this extra spark from the MSD is compensating for the missing trailing.

Ive done it on a 1000HP 20B street car that has a platinum sport in it that seems to have an issue with trailing timing wandering verified by a timing light. Reason we checked is we were getting a large amount of knock with them connected and zero knock with trailing disconnected.

Car runs perfectly without trailing.