bbc clearances
 

My buddy's engine is coming up a little tighter than I've been.
Drag only 427+.030 bbc with GM 1077 aluminum heads, steel rods, older Manley 12.5 pistons turning 7300 tops.

Piston is out .003 and he wants to use a .039 compressed gasket. Piston to wall clearance is .005 -.007, is this quench too tight?

He has loads of piston to valve clearance except radially. He used clay and has .030-.040 at the center of the piston, where the little triangle is. Too tight?

Thanks for any help

Re: bbc clearances
 

The quench is too tight. I can't get away with closer than 0.042" on a 4.165" bore with 0.0055" clearance. That's with a light piston, a light Crower rod, and a really good wrist pin. I'm near touching at that.

For a bracket engine, the valve clearance is too tight for comfort, too.

Re: bbc clearances
 

Like Alan said ,Piston is gonna kiss the head a little . I'd use a.050 or .055 " Cometic gasket .
I'm assuming it's the exhaust thats tight on the radial clearance , you can cheat a little and shift the head with offset dowels and avoid having to cut the pocket.
I did that more than a few times back in the old TRW piston days.
I've run valves that tight myself,but i wouldn't recommend it . they will kiss the piston .