gap for plugs - MSD box & dist.

The old Splitfire ads said they first ran an engine on the dyno with copper plugs, then again with Splitfire and measured ~20% more max power (or such). They didn't relate that the engine was cold in the first run and warmed-up in the second. When ads state, "up to 20% more", that means, "no more than 20%". You could see a 10% drop and still match that claim.

Re gap, I had a bad misfire in our 1996 Plymouth 2.4L when flooring on a freeway onramp. High throttle at low rpm is the worst condition since cylinder pressure is highest. It is harder to throw a spark at higher air pressure. In contrast, sparks easily jump feet in a vacuum chamber. A Chrysler TSB for the turbo version of that engine suggested lowering the spark gap to fix misfires. I reduced mine from spec 60 mil to 50 mil and no more misfires. Judging from later engines, if using the GM HEI ignition module, or similar, you might run 60 mil gap, assuming your plug wires are thick enough to not arc to ground (view idling engine in complete dark, looking for "ghosts" around the plug wires).