I start at .015 & it grows to .020 when hot. Oddly, I noticed with the alum head, I gain clearance when hot. My other stocker (LS6 cast head), does the opposite. Hot at idle is not the same as hot at WOT@7200rpm, so you have to watch it. Some racers, if they are setting the record or running someone heads-up, will tighten it up, but you run the risk of burning a valve.