from the B21/B23 reconditioning manual.

The fixation with having valve guide to stem clearances as tight as you would do on an iron OHV head like a SBC is one that I have always found rather amusing.

Too tight is as bad, and can be worse than, having the clearance on the loose side. The Volvo specs of around 2 thou intake and 3 thou exhaust, witht he max allowable being just under 6 thou for either makes some machinists a bit stir crazy: THAT'S TOO LOOSE!!

NAH!!

I like to have them right at 3 thou in a boost motor. That gives my valves some room to warm up and expand when I am in boost. And I do not have to worry about having any valves seize in the guides. [an occurrence that is NOT pleasant; nor is it inexpensive to correct]

...just one of the little things that helps my motors handle and live with the heat loads of boost.