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Spark plug gap

Ronald Weishaar

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Does anyone have this engine combination? What spark plugs and plug gap are you using? On my 540 cu.in., 10.5 compression with MSD 7AL-2 ignition box, MSD Pro Power coil and Indy 440 EZ-1 heads.
 
We run our race stuff tight .025"-.030"
Never seen an improvement going wider. Less chance of misfire when they're tight.
Doug
 
On my 496, 10.5:1 w a HEI ignition, I run 0.052 gap with my idle AFR set at 14.7 and cruise the same. But mine never gets raced.
 
Years ago the way some racers set plugs was to start with a close gap, and make a run. Open up the gap .005 and make a run. Keep doing that till your time falls off. Go back down .005 to your last gap and run it there.
 
Years ago the way some racers set plugs was to start with a close gap, and make a run. Open up the gap .005 and make a run. Keep doing that till your time falls off. Go back down .005 to your last gap and run it there.
That would be a lengthy process for me as it usually take an hour to pull the plugs and even longer to put them back. The gap I'm using now is.045. before at .035 it would back fire loud like a shogun going off I'm using RC12YC. the engine is in a 68 Dart and long tube headers.
 
Years back I decided to race my 440/493 Charger at the local drag strip that was hosting a race, show and swap event. I put in new plugs gapped at .045, poured in some 110 leaded Sunoco and headed to the track.
While cruising, it ran great. Once I hammered it, it popped, stumbled and ran terrible. My ET was something in the 14s, a full 2 seconds under what I should be running. Back at home, I first checked the air gap in the distributor. It is supposed to be at .008. It widened up to .020! I adjusted it and went out for a drive. It ran just right from that point on. The stock gap of .035 is also the spec suggested for the MP electronic setup but I found the .045 still ran fine.
 
That would be a lengthy process for me as it usually take an hour to pull the plugs and even longer to put them back. The gap I'm using now is.045. before at .035 it would back fire loud like a shogun going off I'm using RC12YC. the engine is in a 68 Dart and long tube headers.
IF you are using the Champion RC-12YC plugs as noted, you must be running a B or RB engine....yes? USUALLY, plugs gapped at 0.045", with a stock type of ignition system (you did not specify the type), a high end end misfire could occur. Gapping the plugs at 0.035" is a standard setting. Backfiring could be caused by a multitude of issues: Lean fuel mixture, vacuum leaks, too much spark advance, faulty ignition coil, or spark plug wire(s). Sometimes, long tube headers (small bore but long length) will cause a reversion with the exhaust gas exiting pulse, causing a lean condition, leading to a backfire condition. Just my opinion of course.
BOB RENTON
 
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