Most Accurate Way to Gap Spark Plugs?


May 25, 2001
Ok, I was wondering exactly which way to gap spark plugs to be EXACTLY on the gap that you want?

For example, I bought NGK UR5 plugs and their gap is .039" out the box. I know the preferred gap on our cars (below 20 psi) is between .032 to .035". I found a .034" on my spark plug wire gapper tool, so I bent the electrode (with the spark plug gapper tool) to get it to what I think is pretty close. Feeling unsatisfied , I then ended up getting a feeler gauge (.034") and put each spark plug on my bench vise and adjusted each spark plug so that when I slip the feeler gauge in the spark plug gap area, there is a slight friction made. The fact that these spark plugs also got that V-groove made it a little more vague.

There must be some kind of other way (or professional tool) that will get spark plug gaps EXACTLY what you want without kind of eyeballing/guessing/trial& error method? At the end of the day, it probably doesn't make a difference if I'm off between .032-.035" variance between each spark plug?
Awesome, I'm definitely getting that!

I did try to put the spark plug between the jaws of the vise and when I tightened it (while putting the feeler gauge in the spark plug gap), it would temporarily compress the ground strap until I loosened the vise (and the ground strap would basically spring back open). This is why I ended up using the little metal piece of the spark plug gapping tool to bend the ground strap to the right position.
What makes you think that, that tool will work any differently than the vise?
I'm not sure if this tool will work any differently than the vise, but it looks like it seems to be a better option.

For now, I'm running with the stock turbo on 93 pump gas (16-17 psi) with TT chip (along with MSD-50s, THDP, magnaflow exhaust)..
Not on Melissa's car (obviously).