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Spark plug gap?

homebrew

NAXJA Forum User
Location
Bremerton, WA
I tried searching didn't really find anything that answered my question. I have a 91 4.0HO running champion truck plugs. I am trying to find the best gap to give me the best combination of performance and fuel economy. I read in JP that you can increase the gap to help a little with MPG, how much is to much??? Thanks in advance. Paul
 
.35 for almost all chrysler products, and even my scouts run this as their specs. Hope that helps

Jeff
 
I've heard that increasing the gap helps mileage also. I don't know of any controlled study of various gap performances, but I usually run my plug gaps about 5 larger than factory specs. So for the 4.0, I run the plugs at 40 instead of 35.

I've also upgraded my plug wires to solid core with a spiral winding to supress radio interference. The solid core wires give a stronger spark, better able to jump the larger gap.

I use Accel "U-Groove" plugs, which apparently spread the spark out to a larger surface area, which is also helpful (if you believe their hype).

And one last note: I've heard that in the summer time, you can get away with a larger gap than in winter, because of harder starting in the winter. Don't know if that's true or not.
 
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