HEI upgrades spark plugs
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From: Lake George NY
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Autolite park plugs to fit the heads with .035" gap and standard heat range to start. Then play with heat range if required. Autolite seem to have a broader heat range to stay clean.
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The bigger gaps came into play to minimize misfires when the leaner mixtures were used to lower tailpipe emissions. The HEI system is a higher energy (the E in HEI), not higher voltage, system to promote a longer spark duration to light off the lean mixture, and also allow for longer plug life to meet the federal emission system durability requirements. The coil output voltage didn't change significantly, as the lower compression ratio engines of that era didn't produce much cylinder pressure. (The plug gap size and cylinder pressure combination is the primary determinant of what the coil output voltage ends up being. 50 kV is a coil insulation rating, and not an indication of what voltage or energy the coil will actually put out.)
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From: BC
The bigger gaps came into play to minimize misfires when the leaner mixtures were used to lower tailpipe emissions. The HEI system is a higher energy (the E in HEI), not higher voltage, system to promote a longer spark duration to light off the lean mixture, and also allow for longer plug life to meet the federal emission system durability requirements. The coil output voltage didn't change significantly, as the lower compression ratio engines of that era didn't produce much cylinder pressure. (The plug gap size and cylinder pressure combination is the primary determinant of what the coil output voltage ends up being. 50 kV is a coil insulation rating, and not an indication of what voltage or energy the coil will actually put out.)
Also, the OP said he was converting to electronic ignition but didn't say HEI. If you are changing over to something like Pertronix stick with the stock plug gap. There is no performance benefit to increasing gap in either situation.
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The title says:
HEI upgrades spark plugs
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Joined: Apr 2006
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From: BC