The GM switch over to a .045 gap when HEI came out was not done for performance reasons.
Spark Plug gap
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
.035" if it has a points system with stock coil; .045" if it has been changed over to HEI or to an electronic spark system with a high voltage coil. {The plug gap is determined by what level of spark energy is available to the plugs. Set it as wide as the ignition system will allow and still provide a reliable spark.}
Thread Starter
Burning Brakes
Joined: Apr 2006
Posts: 765
Likes: 0
From: Houston Texas
.035" if it has a points system with stock coil; .045" if it has been changed over to HEI or to an electronic spark system with a high voltage coil. {The plug gap is determined by what level of spark energy is available to the plugs. Set it as wide as the ignition system will allow and still provide a reliable spark.}
Burning Brakes
Joined: Aug 2005
Posts: 1,164
Likes: 1
From: Europe, France
I agree with what has been said :
0.035" with stock ignition ( points )
Up to 0.045" with HEI or CD electronic ignition ( MSD 6 for instance ),
BUT try it, the bigger the gap is not always the better...
0.035" with stock ignition ( points )
Up to 0.045" with HEI or CD electronic ignition ( MSD 6 for instance ),
BUT try it, the bigger the gap is not always the better...
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
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Instructor
Joined: Jan 2006
Posts: 228
Likes: 1
From: Warwick New York
It is a question of reading your plugs and assessing your proformance and/ or gas mileage depending on what is important to you. Racers use to gap plugs according to spark plug color and constant testing. Some run different gaps in different cylinders for best preformance to adjust for different characteristics in each cylinder. The gap can change the effective heat range of any plugs. HEI in most engines have a wider gap giving better ignition. The HEI was designed to jump a large gap giving a bigger spark. If you check chevy manuals that cover 1972 to 74 you will see the difference in gap from old points to early HEI.
Last edited by captl27; Nov 24, 2009 at 09:48 AM. Reason: add info
