You want the gap as wide as you can, and still be able to jump the gap. The higher the compression, the closer they will need to be. If running any type of turbo/supercharger, they will need to be gapped closer also. The higher the out put of the coil, the wider you can run the gap. I am running 10-1 compression on my 393 with a MSD Digital 6 Plus, with there new HVC II coil, and am running .070 gap. This combination puts out 48,000 volts at 2 full amps compared to 40,000 volts at 1/3 amp of most so called high performance ignition systems.