Valve lash.. Hot /cold ? How hot is hot?

I have only once measured the difference between hot/cold on an engine with iron block/alum heads. It was 0.003". Veeeeery easy to check. In my opinion, too much lash difference is allowed for alum heads. 0.003" for most alum heads, & 0.004" for a tall head [ that has longer valves/taller ports ]. Performance heads usually have s/steel valves; s/s expands at a higher rate, so that needs to be factored in, which means the hot to cold difference will be less.

To check on your engine. Have tools [ & feeler gauges, pen & paper ] ready for quick removal of the valve covers. Drive the car until engine is at normal operating temp. Switch off engine & quickly remove one v/cover. Check for loose rockers, measure the lash & record. Leave overnight to cool down & re-check the lash cold. There is your hot/cold difference.