There few thing which should be adressed too

Better lubricating oils and steel quality allows engines to opperate on higher power without melting.

Better design of valves. Old valves had ton of space between them and engine walls. Thus lot of conbastion agent were escape prior burning, greatly reducing power. Big distance was important for 2 things. First manufacturing was on much lower level and offset could be big. Second steel quality resulted in high expansion of metal, so it was important to leave space to prevent stacking and wall break