TOPIC: Spark Plug gap on Hemi

I've read the gapping instructions and had a question. I've got a Dodge Hemi, which has 2 plugs per cylinder. The instructions say to modify the gap on 1 plug until that cylinder misses, and then reduce and change all the others to match.

Since I've got 2 per cylinder, do I do this the same way (change 1 until cylinder misses), or should I change both per cylinder until a miss?

Thanks!

Harry

Hi Harry

I would adjust one plug and fire for effect, ultimately you want to adjust both plugs... work on one cylinder and start the engine, if there is no misfire proceed to the next cylinder and repeat. If there is a misfire reduce the gap by .001 - .002 at a time to get a working value.

You only want to increase the gap by 20%, ex. if they were original .042 you would increase them by .008 giving it a new gap of .050.


Karl Fortner
Tacoma, Wa.

That's what I planned on. my "OEM" gam is supposed to be 0.045, with 20% being 0.009.

My question, though, is that I know I need to work with 1 cylinder to determine the ultimate gap for the other 7. In my case, however, I have 2 plugs for each cylinder.

Do I regap 1 until it misses/hickups, or do I regap both for that cylinder until a miss?

I don't know if that will ... never mind. I just found some more information explainging why the hemi has 2 plugs. I thought it was some kind of timed firing for better HP/performance. Actaully, it's only 1 firing on the upstroke, the 2nd first on the downstroke. It's evidently for emissions, not performance.

So, if I can figure out which one fires on the upstroke, that's the one I should mess with.

Thanks!