how much timing should i bump off my motor (b18b1 / b16 head 12.1cr) to safely run a 50? or 75? i know on a stock it's close to -2 for a 75 and 1 step colder plugs - should i even do it? lol would i be safe with like a 35 shot - or should i just dump my pistons and get like 10.5's or something..