The Stovebolt Site Forums The Shop Area The Electrical Bay HEI Wires - Do MM Mater?

I see in ads for HEI ignition wires a number of sizes from 8mm through 10.5mm. Is bigger better? Are there other things to consider?

When HEI ignition was invented to comply with the 50,000 mile "service free" exhaust emission requirement of the Clean Air Act of 1968, there was a concern about the 50KV+ open circuit voltage capability of the coils they had to use being able to jump through the insulation of the 7MM wires commonly in use at the time. HEI wires on OEM systems became 8MM. The concern was somewhat misplaced, as a clean, properly gapped spark plug will fire at less than 10KV, regardless of what style of ignition system is used. There is NO WAY for firing voltage to rise higher than the voltage required to fire the plugs, so people who buy "flamethrower" coils and other P.T. Barnum Special ignition components like huge diameter wires are a prime example of his adage that "There's a sucker born every minute!" "A fool and his money are soon parted" has been true since the beginning of commerce centuries ago.
Jerry

Thanks Jerry, as a buyer of a Flamethrower coil I bought the hype. As it happens, I'm thinking of the new HEI dizzy which has a coil built into the cap so no coil is needed at all. Perhaps I can find another sucker like myself on Ebay . . .

If I understand you, 8mm is good enough. I notice a wide variety of prices, is there anything to choose from outside of price & color?

Paul,

I have the HEI dizzy and my truck runs really well. I have not had it down the road as of yet, but it looks good and only the future will tell!

Chris

Newer "small cap" HEI's use 7MM wires, so the 8's would be fine, I'm sure. They also fit the terminals on big-diameter caps correctly. The large diameter cap and rotor was also designed to combat a mostly nonexistent concern about crossfiring that's been pretty much debunked. Now, if plug gaps get huge due to neglect, or a plug wire falls off, then the coil has enough open circuit voltage available to jump right through coil insulation, etc. As long as the voltage has somewhere normal to go, any size wire is probably OK.
Jerry

Very good, 45 thou on the gap with HEI as I understand it.

A .045 gap on a plug with a clean, squared-off center electrode will fire at light throttle at around 6-10 KV. On snap acceleration the firing line on a scope will jump up to around 15-18 KV. As the plug wears and the electrode gets rounded off and the gap gets wider, the firing voltage will go up to around 15-20K during light load operation. When the loaded voltage approaches 30-35 KV the plug will develop an intermittent miss. Leaner than normal mixtures will require higher voltages to fire them. In the late 1980's GM experimented with extremely lean mixtures and a plug gap of .080" in hopes that enough combustible mixture would find its way between the center electrode and ground to light off. Those engines would miss if the gap was set to 35-40 thousandths, but would run pretty good at 80. Firing lines in the high 40KV ranges were pretty common on those engines. Even slightly dirty or worn plugs would miss.
Jerry