EI on top plugs

Why are the top plugs used for EI rather than the bottom which have a greater tendency to foul. Using the hotter stronger spark of the EI would seem to be better on the bottom plugs to me, but I have little real knowledge of electronic ignition.

Someone please enlighten me.......


Glenn Wilkinson

People who put the EI on the top plugs do it for simplicity.
If you have a choice, it's better to have it on the lower plugs.

Actually

Klaus recommends putting it on top. Best ask him why!

Not always the case ...

glenn654 said:

Why are the top plugs used for EI rather than the bottom which have a greater tendency to foul. Using the hotter stronger spark of the EI would seem to be better on the bottom plugs to me, but I have little real knowledge of electronic ignition.

Someone please enlighten me.......


Glenn Wilkinson

Click to expand...

The "Jeff Rose"/ElectroAir Systems recommend using the BOTTOM plugs.

So ... it varies. There is no single approach although I think Klaus (Lightspeed) recommended the top.

James

Ease of service on the top and with the spark these EI's put out, good fuel burn for sure... with proper leaning the bottom plugs stay very clean.

I may be wrong but I don't think it is actually the quality of the spark that keeps the plug clean it is the quality of the combustion of the air/fuel mixture. If you have good combustion then the entire cylinder head area will be clean including the spark plug. Weaker spark plugs, like those on the magneto, produce a lower intensity spark which may cause a less complete burn and leave deposits behind which ultimately clog the plug. Even a good plug in an engine that is timed badly, runs too righ or has a lot of oil leaks may become fouled no matter how intense the spark is.

Don't know but I....

I, being of the lazy type, chose to run the the same plugs as the mag did. I could see no reason for rerouting plug wires from the remaining mag so I left them alone. So my EI runs the top plugs on one side and the bottom plugs on the other.

I previously had a LSE Plasma I on my -6, and they did/do recommend running them on the top plugs. I asked them why once (after thinking about the bottom plug fouling issue) but didn't get much traction on the Q. I do know that making short runs from the ignition coils (often mounted on top of the engine or on the firewall) to the plugs is a desireable state, so perhaps its just easier to do on top.

I recently installed a new Electroair system, and asked Mike there about using the top plugs, as I didn't want to change out my mag harness. Mike said it would be no problem, and it has run very well so far.

One thought I had was that it is recommended (from my install manual) that the EI spark plug wires not be run closer than 1/4" apart, and maybe that is easier to accomplish topside too (it was for me anyway).

Just another $0.02

Cheers,
Bob

Glenn,
I agree with Klaus on the top plugs as my first choice because of the air/fuel ratio based on stock injector location and/or air/fuel mixture characteristics for the carbureted engines. Top plug is in the best location for the first crisp ignition event.
Since my G3i system runs all the plugs on EI I only have to give my insight on the 1/2 EI system based on conventional magneto drop rpm on run-up. Previously before developing the G3i system, on my supercharged IO-540. My left mag fired all the bottom plugs and the right all top (still with EI), The fuel injectors face upward on this engine. Mag drop @ 2000 was always 15 rpm more on the right over the left. If I had my mixture a little to the richer side, the right mag drop was 20 to 25 more than the left. I know my fuel set-up is not your typical stock set-up, but has shown mag drop that my lower plugs were in a more correct "power" air/fuel ratio. However with the stock position injector facing down, this keeps the top plug in a more combustible "power" air/fuel mixture. I'm curious, if any other bottom/top L/R mag set-ups out there and their mag drops on this theory?
Thomas Shpakow
G3i