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 Spark plug strap reading 
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Joined: Sun May 12, 2013 5:21 am
Posts: 332
Location: Michigan
I've herd/read different views on what the strap means in the past and wonder what other think and why.

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Mon Aug 08, 2016 7:52 am
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Joined: Thu May 08, 2014 7:47 pm
Posts: 235
Strap tells me how hot the burn is.


Tue Aug 09, 2016 4:33 pm
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Joined: Sun May 12, 2013 5:21 am
Posts: 332
Location: Michigan
So you use it for heat range or timing?

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Tue Aug 09, 2016 5:23 pm
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Joined: Thu May 08, 2014 7:47 pm
Posts: 235
When the heat range of the plug changes, so does everything else about the plug. Conductor length, the thickness of the insulation around it, and how far it protrudes into the flame front. Projection style plugs have long conductors, that push the spark into the flame front. the further a plug protrudes into the combustion chamber, the further away from the insulation of the head, the longer and thinner the insulation around the conductor is, and the ground strap is also longer and thinner as a result of this hot plug, it stays hot, and doesnt transfer heat well, especially in high load situation.


The plug will start to glow under rising temp an pressure of on compression stroke, and pre igniton of the charge will occur because the plug is to hot, and has glowing ground strap.

Say that instance right there caused a dead misfire. So you pull the plugs. all look good but the hottest cylinder......and that is because the ground strap has got so hot, it melted and torched right off by excessive cylinder pressure and temp caused by the explosion that took place, instead of a fast burn that should have taken place. The conditions just flat out ran over the tune up. And by that i mean, octane, plug heat range, combustion chamber & cylinder temp, and timing.

If the shock wave from the pre ignited flame front, on the compression stroke, colliding with the piston is great enough, the shock wave rattles the piston so hard in the bore, it can shatter, or break ring lands. Keep it knocking, and cylinder temp and pressure rises exponentially, keep that up long enough, it will blow the strap off first, then start hammering away, and the porcelain, and the porcelain pieces will bounce around in the cylinder, getting hammered fucking everything up. excessive cylinder pressure and temp, pushing on the head gasket, egg shaping cylinder walls, hammering the piston, something has got to give first.

I look at the plug as a fuse. when things get hot, i want it to blow the strap off before it hurts anything. Some race plugs will burn a whole in the piston before they even show any heat on the ground strap.

Alcohol motors don't leave a carbon trace, so the only thing you have to tune with is how hot the plug looks.


Wed Aug 10, 2016 6:28 pm
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