Originally Posted by burkgul
I will rebuild and port a pair of old GM sbc low comp heads for a supercharged 350. Right now I have two different castings to work on:
3998991 72-73 307/350 75cc 1.71"/1.5"
3997993 72-73 307/350 75cc 1.94"/1.5"
I plan on using a kit from Competition Products, #851326, and manganese bronze valve guides to rebuild the heads. The kit includes 2.02"/1.6" stainless steel valves, firstname.lastname@example.org"/email@example.com" 0.570"max lift valve springs, 7deg CrMo retainers and valve locks and umbrella valve seals.
Witch of the castings should I use? Or is their better flowing low comp castings to look fore?
These are early thin wall castings, I rather doubt they'll stand up to blower pressures for long. The problem everybody has with blowers (Ford, Chrysler, GM, the imports) is that the combustion chamber flexes and finally breaks with a rush of coolant into the cylinder. True blower heads usually include some extra support thru additional material thickness and some posts cast in to connect the chamber roof to the rocker box deck to spread the loads out over more structure.
My experience says you're being "penny wise and pound foolish".