Could someone explain the effects of different plug gaps, and what would be the "sweet spot" gap for a I/H/C/car in the 390 rwhp range?

TIA!
Mike B.

 

I dont know about sweet spots but here is some
info that may help your question.

http://ls1info.com/article.php?sid=46

here is some moreinfo that I found..

The NGK plugs seem to work best in the LS1, but there are three different choices. The
TR5s and TR55s are the stock heat range plugs, their only difference being the preset
gap. The TR5s come out of the box at .039, while the TR55s come at .059. NGK recommends only
changing the preset gap by plus or minus .010, so choose the plug you want based on which gap
you plan on running. The third choice in plugs is the TR6, which is one step colder and is
pregapped at .039. You can run this plug on a normally aspirated application, but remember that
it won't last as long. It depends on the type of driving you do, however expect a TR6 to last about
10-15k, and the TR5s and TR55s should be good for 15-20k quite easily.