HEI

[TerryH]

Hi guys getting to swap out my points for a new HEI and and going to make up the my wires but wondering now that I am do I need to change the gap in my plugs..I hear yes and no..have a 428 bonneville

[Stripes]

An HEI puts nearly double the amperage to the plugs than a point ignition. Pontiac increased the gap from .035 to .060 when the HEI was initially introduced. In the years after that, many moved back to a .045 gap feeling the .060 was excessive. It will not hurt it to run any of those gaps, so the best way to know is to test your application. I run a .045 gap in my 469 with a factory HEI, and it likes it.

Remember, the most common issue with HEI swaps is the points style distributor had a resistance wire powering it limiting voltage but primarily amperage to the point set. An HEI needs full voltage and plenty of current to operate at its peak.  So run no resistor or resistance wire and ensure you have at least a 12 gauge or larger wire supplying power. You have to verify that with the engine running.

 

[Topless]

So the answer is: you don't have to change the spark plug gap, but it may run better if you move it up to .045.

Remember to check your total timing as many HEI's put in too much mechanical advance.