Old timer`s advice on spark plug gap finally clicked for me

For years I just set plugs to whatever the book said and called it good. Then this retired mechanic watches me doing a tune up on a 5.7 Hemi and tells me I was leaving power on the table by a couple hundredths. He showed me how to read the plug and adjust for the actual fuel mix in that specific engine. I changed my gap from .045 to .048 and the truck idled smoother and felt stronger on the test drive. Anybody else get schooled by an old timer on something they thought they had down?

2 comments

2 Comments

oliver_mitchell14d ago

That .003 difference really makes you wonder about all those "factory spec" numbers, doesn't it? My old man taught me the same trick back when I was building a 350 Chevy in the driveway. He always said the book gap was just a starting point, not the final word. Did he walk you through how to read the ground strap color to figure out if you need to go up or down next time? That's the part that took me forever to get right, you know, looking for the little heat ring at the bend and knowing what it means for the fuel mixture.

dakota_singh3913d ago

The fuel mixture angle is solid, but one thing people skip is how the spark plug reach changes everything. I've got a buddy who fought a misfire for weeks until he realized the plugs were 1/16" too long and the tip was barely poking into the chamber. That little difference in thread length can make your gap readings useless because the electrode isn't sitting where it should. Your dad's heat ring trick still works, but check the plug number first to be sure the reach matches your heads.