Spark plug gap - Team Camaro Tech
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post #1 of 8 (permalink) Old Dec 31st, 08, 06:48 AM Thread Starter
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Spark plug gap

Can an increased plug gap cause detonation? Thx!
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post #2 of 8 (permalink) Old Dec 31st, 08, 06:58 AM
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Re: Spark plug gap

yes it can ,bad gas , timing off ,......lots of factors...give a little more info on your car and whats its doing and when??
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post #3 of 8 (permalink) Old Dec 31st, 08, 11:11 AM Thread Starter
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Re: Spark plug gap

Thx! Long story but here is the Reader's Digest version: I have a 383 with 9 1/2 to 1 compression and Holley aluminum heads that had Autolite race plugs. It worked fine. A mechanic told me to go to a warmer plug and it seemed to work but now it pings at above 3500 RPM or so when I get on it. I have regular Autolite 3923's in it now with the timing only at 11 degrees. Total is about 32 degrees with an HEI MSD distributor. I may go back to the racing plugs coz I don't worry about fouling because I don't "baby" it. Or I may go to the 3922's since they are one step colder. I hate to go through the hassle of changing the plugs if I have to do it again if the 3922's don't work. I would then go to the racing plugs. maybe I should just go straight to the racing plugs and skip going to the one step colder 3922's. Thx! DeAngelo
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post #4 of 8 (permalink) Old Dec 31st, 08, 12:22 PM
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Re: Spark plug gap

The colder the plug, the faster the plug dissipates heat, especially with alum heads, the more rpm needed to keep the electrodes hot to burn off the deposits.

Lower the operating rpm, now the colder plugs become fouled quicker. Its like an "either/or" situation, high rpm, colder plug, lower rpm, hotter plug.

A wider gap has a shorter spark in duration with a high potential, meaning more kilovolts compared to a smaller gapped plug, longer time with lower kilovolts. It all depends on how much the coil is designed to be saturated with current running through it. Higher rpm, shorter amount of time to saturate the coil, less spark potential. HEI's generally allow 0.045" gap; some were up to the 0.060" gap.

All said, I'd stick with the plug type installed in the engine when delivered.

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post #5 of 8 (permalink) Old Dec 31st, 08, 05:45 PM Thread Starter
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Re: Spark plug gap

Thx, Everett! I agree!! The plugs in it were Autolite racing plugs (AR series). They had a very short electrode. It seemed to be cut in half. What is the purpose of that? Anyway, they worked great but I switched to a warmer plug (3924) because a mechanic I know suggested it. It pinged a bit. I then went to a 3923 plug and it helped. The AC Delco Rapid Fires were CRAP! I could barely step on it without it starting to rattle like a tin can!!! As soon as I went back to the Autolite copper cores, it worked like a champ. Well, now it is starting to ping a bit when I hit 4 grand or so. I may need to check my fuel mixture as well. I really don't have to worry about fouling cold plugs because when I drive, I GET ON IT!!! I don't "cruise", I stomp on it. That should create enough heat for those cold plugs to burn off any carbon deposits. Thx again! Hope to see you around one day! DeAngelo
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post #6 of 8 (permalink) Old Dec 31st, 08, 06:07 PM
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Re: Spark plug gap

[quote=Deangelo66;1129746]Thx, Everett! I agree!! The plugs in it were Autolite racing plugs (AR series). They had a very short electrode. It seemed to be cut in half. What is the purpose of that?

Are you referring to the ground strap cut back vs electrode?
Assuming so..it is akin to indexing spark plugs.The cut back ground strap will allow the spark energy to find any available kernel to light off vs hiding behind a full length ground strap.

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post #7 of 8 (permalink) Old Dec 31st, 08, 07:49 PM
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Re: Spark plug gap

Is your MSD HEI dist a "large cap" type, and does it have a vacuum advance unit? Why don't you go to the MSD web site and ask about plug heat range and proper gap in their forums? http://www.msdignition.com/forum/index.php

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post #8 of 8 (permalink) Old Jan 2nd, 09, 09:07 AM Thread Starter
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Re: Spark plug gap

Thx Fatblock and LS427. Yes, I was talking about the strap. And that makes sense. And I have an MSD Pro-Billet Ready-To-Run Distributor 8360. http://store.summitracing.com/partde...5&autoview=sku I will check the MSD site. It had Autolite AR3933 plugs in it when built. Thanks. D
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