I'm finally starting my initial racemotor mockup. I'm pretty tight on the exhaust valve to cylinder wall clearance, even after eyebrowing. I'm under 1/32" clearance, about .025, at max valve lift. Here's the numbers I've got: an early E88 head, milled .030, using .025 cam tower shims, intake and exhaust valves at 44mm and 35mm, L24 block at .040 over, .535 lift in/exh cam, comp head gasket measuring .056 before crush and assuming .047 after. Cylinder eyebrowing can't go any deeper and keep enough room above the top piston ring land. Wider eyebrowing is not an issue, depth is. Current eyebrowing has already dropped CR from 12:1 to 11.7:1. Exh valve clearance at rocker/cam set at .010, intake at .008.
Questions - Has anyone gone this tight on a valve-to-cylinder wall clearance before? If so, what was the outcome? How much can you decrease exh valve clearance at the rocker/cam before you run into problems? How does a manufacturer regrind a new cam to take a little lift off? (Isky L1)
I'd prefer not to use a thicker gasket and loose more CR. Some options are a little less cam (down to .510 or so), another set of pistons with a lower top ring (more $$ and less CR), or ??? In retrospect I would have stayed with the stock exhaust valve, but now that I've finally got the cylinder head the way I want it, and I don't want to re-do it.