Whats the difference between the gap in spark plugs? will one gap perform better then the other? i have a pair of NGK plugs with a .035 gap and AC Delco R45TS's with a .045 gap. I noticed that the AC Delco plugs ran better but they are also the stock heat range while the NGK's are one hotter (which is what the builder put in the engine).

 

A larger gap will give a bigger spark, but to fire a larger gap requires more voltage, which the ignition system may or may not be able to provide. Higher compression, and high RPM make firing a plug more difficult, and a smaller gap may be needed to prevent misfire. Heat range depends on how the engine is built and used. High compression and high speed driving usually calls for a colder plug to prevent preignition, low compression and tooling around city streets usually calls for a hotter plug to prevent fouling. For a stock engine factory installed plugs usually work best.

 

If your engine is new enough to have either factory HEI, or aftermarket like an MSD 6A or 6AL, then the .045 gap will work. If it's an older stock distributor you need to stick with the .035 gap.