[66sprint6]

Has anyone ever upgraded your HEI ignition with an aftermarket coil from, say, Accel or another company? My friend seems to thnk that it will make a difference and he spent 200.00 on the coil and control module. I googled it and saw that the benefit is that you can increase the sparkplug gap, creating better fuel burn. I told him that a real GM HEI ignition is pretty good and hard to improve upon.

[77 TRASHCAN]

Your friend wasted $200.00, period.
The best module for the HEI dist is the stock, old timey 990 module. A stock coil works!!!

[firechicken]

Waste of money.
Don't believe the hype.

[Formulabruce]

I have updated them since 1975, even for customers at the dealership. We did so many, we bought them from the junk yard.

[george kujanski]

You can increase the gap with the OEM HEI. One of my cars lists .060 as the gap. I use about .045.

What happens if the gap is too wide is that other weak parts of the system start to get stressed. the cap, the wires, etc. In humid conditions they will show up as misfires, the voltage leaking off the wires because the discharge path from the wires to metal is easier than thru the plugs.

george

[mgarblik]

A stock HEI has tremendous spark energy and voltage potential. Open a wire with one running on a scope and 50-60 KV is not out of the question. As mentioned, they pack so much energy they expose weakness in the rest of the system. Wires, Cap, and rotor specifically. Other than fitment issues with certain intakes and such, the large cap HEI is hard to beat. Many late 70's engines specified .080" gaps on the copper plugs. That's pretty wide. An HEI will jump a 1 1/2" gap in the open air to ground. I would think the $200.00 worth of probably Chinese aftermarket parts is mostly crap. I have had good luck with NAPA Echlin branded parts for replacement parts when Delco was not available. Other brands, not so much.