Breathing new life into the 318 in the Scamp!

I get ya, but .490" lift is solidly .080" more than ANY factory 318 cam...perhaps a smidge more. And many of those factory 318s still had some valve relief. Furthermore, you've already illustrated in post #52 that even a stock cam either with stuck valves or over-revving (floating) will kiss a stock piston with no reliefs...clearly a bad thing. P/V clearance isn't about just lift either...0.050" duration and overall cam timing plays a significant part in that measurement as well, and I'm guessing that 210/219 split pattern cam is at least 15-20* larger than the stock 318 cam.

You're correct in asserting 340 pistons are higher in the bore...high compression 340s were actually 0.040" out of the hole, but X and J heads have a quench relief pad in the combustion chamber for that purpose, and their valve reliefs are rather large to compensate for a factory cam of over .440" lift.

If I had to guess, unless you've shaved down/equalized the decks to true spec (9.58" if memory serves), those stock slugs should be anywhere from 0.030"-0.060" in the hole. I'm not trying to tell you how to build your engine-that's yours to do, but I'd hate to hear you put everything together and see a horror story about this thing eating itself.