Valve lash
When I am initially set valve lash cold on an aluminum headed, iron block engine,
I take the cam builders hot specs and go .004" loose cold. When the engine is fully up to temperature and heat soaked for a little while, I recheck the lash and see what the difference from spec is. I correct it to spec.
I use the difference I saw warm to change the cold setting. Next time I check it hot again to see if it is right.
I don't vary hot lash from spec except to see if it is faster with .004" less or more lash seperately on the intake and then the exhaust.. Then I go back to spec. If I want to go faster, I go back to the cam guy and tell him the results and have a different cam ground for that combination.
On an iron head/block, I go .004" tighter cold and recheck hot.