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Old 10-04-2010, 10:45 AM
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HEI coil voltage

How much additional voltage can a stock HEI handle from an aftermarket high voltage coil? I've got a 65,000v coil but was wondering if it would be too much for it. Thanks.

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Old 10-04-2010, 03:49 PM
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It doesn't matter. As long as you have a decent cap and wires. The internals of the HEI only care about the primary voltage and resistance not the secondary voltage.
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Old 10-05-2010, 03:24 AM
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Stock cap and pro comp 10.2mm spiral wires. Guess I'll give it a shot next weekend. Thanks!
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Old 10-16-2013, 08:05 AM
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Good to here someone working with a 318. I love Mopar. I do know one thing about the H.E.I. . They are power hungry. That stock wire my 72 Chevy Pick-up was too small. I put a 12gage wire to the B+. You will find guys tying an electric choke into this primary wire too. The buzz noise is puzzling though. What comes to my mind right off is there is too much load on it, but why at idle only. You don't have a ballast resister in the circuit somewhere do you.
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Old 10-16-2013, 09:02 AM
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The two questions you need to ask are one, how does the 65KV coil produce the higher voltage, and two, how much more heat will it produce? Heat is the enemy of all electronic components and remember the HEI lives by a small internally mounted electronic module.

A quick answer to both questions is that the higher voltage coil produces higher voltage by reducing the primary coil winding count and increasing the secondary winding count. Reducing the primary windings raises primary current load. The little HEI module has to take this load. The higher ratio of primary to secondary windings also increases the inductive "kick back" through the primary circuit as the coil fires. These factors weight heavy on the life expectancy of the module. The higher primary current and the higher KV output also creates alot more heat which further decreases the life of the module.

Companies like DUI that produce high output HEIs take these factors into account and use components that are better suited to the task. I have seen too many failed HEI modules where a high output coil was added to ever recommend it. I guess if you use the vehicle only for drag racing and trailer it to the track, that's one thing. But if you want reliability, think twice about running the 65KV coil in your stock HEI.

An externally mounted coil helps remove some of the heat load but the only sure way to run high KV and keep it reliable is an add on module like the MSD. The add on module takes the heavy current load off the little HEI module and you can run all the coil you want. The new digital add ons are best for this.
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