i am planning on upgrading my factory HEI ignition system on my 89' Vette (cap in coil style), and was wondering what i should set the spark plug gap at. im planning on using: MSD 8.5mm wires, ACCEL cap&rotor, ACCEL supercoil, and a ACCEL module. with all this increased spark energy over the stock system, and the MSD wires superlow resistance, would a gap of .050 be ok? also, which plugs would you recommend: Rapidfires because of their copper conductors, or Bosch platinums because they last longer?

 

For my 406, I use the factory plug gap of .035". For spark plugs, I use standard Champion RC12YC plugs or it's AC Delco equivelant. Plugs are changed every other oil change. Never saw the need to go with anything else. At the most, I'd play around with the plug's heat range til I find one that runs the best with my combination, going hotter with N/A applications and colder with forced induction.

 

You could probably go .05 over stock with that setup, long as you stay away from nitrous and blowers. As far as the plugs, I hate the rapidfires. If your gonna do all that get yourself a good ignition box as well and then you'll be all set to go on with future mods.

 

I run HyperTech coil/cap/rotor (53kV), TPIS wires (lower resistance than stock but look stock) and AC Delco plugs with cjt-back ground electrodes gapped to .048" in my '88 Vette. The IROC has the same setup except it has the MSD SuperConductors.

The MSD SuperConductors are a "better" wire if you don't need stock look; the TPIS are still much lower resistance than the stock.

If that ACCEL dist setup puts out enough kV you can open up your spark plug gap too, if not stay closer to .035".

This combo with the cut-back plugs netted (a repeatable) 1mph more at the traps or 10hp along with a little better mileage due to the more complete charge burn.