Quote:

Would anyone happen to know the intake valve closeing on the XE284H? I'm at 10.9x, but i have heart shaped combustion chambered heads & FTs around .025" below, quench will be around .060-.065", not the best but not bad, Looks like if i can stay in the 70s on intake valve closeing i should be fine, maybe even in the mid-upper 60s.

if you use a mechanical cam with assymetrical lobes you can play with the intake closing events by juggling the lash around. i use a cam like this on my 65 coronet. spreading the LSA and not doing a bunch of advance on the cam can help. from my experience 10.9:1 is high for pump gas. my 69 r/t has the 180psi engine and the intake closes around 68 degrees ABDC and its not tolerant of total timing above 35 degrees, easy to get detonation. the 160psi engine with the mechanical cam gets pretty touchy at 37-38 degrees total; so i keep it around 36 degrees. i don't have much faith in a lot of the internet hype about using high compression numbers with pump gas. my experience says 9.5:1 is the practical limit with iron heads. juggling the dynamic compression can help some but after a point its a dog chasing its tail. a lot of factors involved.