spark plug gap formula?

[Joseph Upson]

Using different wires on the same engine can contribute to the problem as a result of different wire resistance and induction interference. Given the physics involved, I would never run a wider gap than the engine was designed and tested to run with.

Some things are constant no matter what you do and in this case I don't believe there is any benefit in the long run from running a wider spark gap because it weakens the intensity of the spark which needs to be within a certain range to properly light off the air fuel mixture and shortens the amount of wear necessary to reach a point where the spark gap is inefficiently wide.

I've seen tests that have shown that high energy aftermarket ignition parts (coils and wires) improve performance and that has to be a function of increased spark intensity and decreased resistance which if you're not careful an overly wide plug gap can counter.

I learned at an early age before I knew much about engines while experimenting with the plug gap on an 8 hp lawnmower engine that a yellow spark (weak) from an extra wide gap would barely to not at all ignite the fuel and would foul out the plug and that a blue spark would ignite the mix everytime and the plug would stay clean.

On ignition parts I try to stay equal to or better than OE and that means no Autozone ignition parts or the like unless they have AC-Delco or a name brand aftermarket label stamped on them.

Stop playing with fire and shorten those gaps so you can keep the fire hot. That was one of the last things I did before the 3.9 finally fired up again and continued to do so effortlessly each time afterwards.

[sprucegagt]

Getting back on topic.

ok, i imagine i should be just fine at .060 or close to it.. 10.5 isnt that much more than 9.8 i wouldnt think.. maybe i will go out and buy new coils for the hell of it, i have to get thing done... what size wires are you running? what is too big?

has any1 ever revved there engine at night from under the hood with no light? as in more than one good rev in a row

10.5:1 compression is not to much for the stock ignition system. I don't think the wires are your problem, since changing out 4 different sets have not stopped your problem. Have you tried using new plugs?

[Joseph Upson]

Getting back on topic.
10.5:1 compression is not to much for the stock ignition system. I don't think the wires are your problem, since changing out 4 different sets have not stopped your problem. Have you tried using new plugs?

Someone posted here a little over a week ago about new plug wires on a saturn and a miss or poor running condition that went away as soon as the plug wires were rearranged, that prompted a question about whether it mattered which terminal on the designated coil pack a cylinder was connected to, which we are aware it does not.

Electromagnetic induction can be a real problem as evidenced by what happened with my CPS signal when I untwisted the wires. I have revved my engine in the dark at times in an effort to detect bad ignition parts and it is very effective at doing this because you are not suppose to see sparks outside of the plug wires or the coil.

The plugs as mentioned can be incorrect for the application also, some have built in resistances according to my GM FI manual which lists 3 ranges:

AC numeric codes 41-XXX.
500-599= non resistor.
600-799= resistor applications.
800-999= special metal (platinum tipped) resistor applications.

[sprucegagt]

/\ I agree. But having multiple wire sets failing, is a little more than just bad wire routing or plug gap.

[Alxsmt]

yep changed the plugs too. using the older style ones, not the $8 a piece.. (i believe 3100)

i dont really think its the wires but the guy that helped me build the engine insists on me getting some new ones so i did... same guy also said the iradum(sp?) plugs may have different resistance or something like that, he was going to look up the metal propertys or something to find out for sure. ive been told on here it makes no performance difference at all, just plug life

does any1 know why 3400s run a bigger gap than 3100s? i thought everything was identical electrical

[SappySE107]

What year? gen 3 should all be the same gap. Iridium plugs act like you have a hotter coil and they are self cleaning (unless its really bad). I would keep using them. GM uses them on the 3500 stock.

I prefer Magnecor wires but I don't know if they would help either.

[geldartb]

04+ 3400's got the iridium plugs from the factory too. the 05 3400 i got had them in there

[Alxsmt]

i cant rember exactly, the r44ltsm6 plugs, i could even be thinking 3.1. since that is true i guess im going to go out and buy some new plugs again lol. today i pulled my LIM off to change the gasket (had a small oil leak and that was the last thing to change) i had a cracked gasket on the back right cylinder (cant think of the number), not sure if it was there b4 or if i managed to crack it somehow pulling the plenum. doesnt act like a vaccume leak and i cant hear one but maybe that will fix my miss lol

[geldartb]

these ones are the normal plugs r44ltsm6. there working pretty good in my setup.

[Alxsmt]

so turns out my miss wasnt electrical! its gone now. guess im gonna toss my msd wires on when i get them to see if it fixes my blue wire syndrom. if not oh well i dont care as long as it doesnt miss

[Azrael]

Oddly enough, the recommended gap for ACdelco Rapidfires is 0.45" (#6) for my old 3100 while all other compatible plugs call for 0.60".