Stopping the knock: Lower compression and ported heads...
Would you elaborate on that? What dynamics would affect a solid lifter movement at .050 if valve lash is anywhere from .010-.030"? How is solid lifter motion any different in a running vs. not running engine? Is the effect different at different rpms?
It's the way the opening and closing of the valve is effected by the lash in conjunction with the lobe. Of course the lobe never changes but lash greatly effects the valve timing. Give it 1.000" lash or remove the pushrod and the valve never opens.
What opened my eyes was the day that I began to play with the valve lash on a solid lifter cam and test the cranking compression. The tighter the valve lash, the less cranking compression, increasing the lash gave me more cranking compression. The hydraulic cam runs zero lash, put solid lifters on a hydraulic cam and give it .020" lash and you've shortened the duration and the valve will open later and CLOSE earlier, bingo, greater cranking compression, higher dynamic compression. (And with that much lash on a hydraulic cam you'll probably destroy the cam, this was for illustration purposes only.)
It's the reason less lash will give you more top end and more lash will make the engine pull harder on the bottom.
On the dyno, we open and close the lash on the intake and exhaust as a cheap way to see if the engine wants a bigger or smaller cam, without having to buy a $130-$330 cam. Increase the lash on the exhaust and see what happens. Power increase? You might be able to use a smaller exhaust lobe. Power loss? Tighten the lash and see if it wants a bigger exhaust lobe. And blah, blah, blah, opening and closing the lash on the intake and exhaust to see how it effects the power curve Then make your best guess and re-order the cam you want for the engine's purpose.