I want to buy one step colder plugs (ngk) what is everyone talking about when they gaps. What's a .35 gap? What gap size do I need?

 

The biggest you can run without spark blow out . Anywhere from .025 (small) to .040 (bigger) . With the mod's in your sig .035 would be a good place to start, but every car is different so testing a bunch of different ones is the best idea.