What Should My Spark Plug Gap Be?

Questions or Problems contact us at: Ph.: 330-540-7223 or email brad@race-1.com

(all information below is a recommendation from Race-1 not necessarily from GM)


FIRST, there is no such thing as a 'magical' spark plug.

We are constantly hearing of “special” spark plugs that increase horse power and/or have decreased lap times.

If your spark plug is of the correct design and heat range AND was gapped properly it WILL PERFORM AS WELL AS OR BETTER THAN THE “magical” plugs.

Usually, when a racer claims to see a substantial gain from his new magical plugs—those new plugs did not require gapping. When the gapping procedure is left to the user it can easily be done incorrectly—causing an improper output thus inhibiting performance.

Now, for the proper gapping procedure...



Chevrolet Performance recommends .045 as the correct gap for both 602 and 604 engines.

Many tuners and engine builders follow this recommendation and may even increase it a small amount as top-end power numbers can possibly increase with a wider gap.

“The small gains that are created with wide gaps are not worth a fouled plug on restarts,” states Brad Hibbard of Race-1.

"How the plug is gapped is also very important," says Hibbard. The ground strap should be square and straight (as shown). The electrode should never be forced upon when gapping (use the “Go No Go” Gapping System). DO NOT PRY ON THE ELECTRODE.

Race-1’s ‘Ready-To-Run’ Spark Plugs (part #: CII-NGK8) are sold with the gap already adjusted. Our adjustment process is as follows:

  • The ground strap is bent up with a tool that only touches the strap and not the electrode.
  • The strap is pulled back down straight and square to the electrode.
  • A “Go No Go” Gapping System is used where .035 goes in and touching nothing and a .040 will not start into the gap.
  • A round style wire gap tool is used.
  • Net gap: .037.
  • In addition, Race-1 applies the proper thread lubricant, and the proper amount of the lubricant, on the threads. Note: Neither Never-Seez nor Anti-Seize should ever be used.

(The “Go No Go” Gapping System is as follows: Though it is possible to set the gap using one gauge, it is much easier and often more accurate to use two. Let's say you want to set the gap at .037". Use the .035" and the .040" gauges. When you can insert the .035" gauge between the ground strap and electrode without touching both of them, the gap is wide enough. To make sure it is not too wide, remove the .035" gauge and attempt to insert the .040" gauge. If the wider gauge can only be inserted touching both points, you have the correct gap. This is called the "Go-No-Go" method. One gauge goes through, the other doesn't.)

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