150 HP LA 318 - vs - 230 HP Magnum 318

Closed chamber 273 heads, like the 920's, would increase the compression a bit (one point at best?) while still using the small 273/318 sized valves and ports. The 340/360 heads reduce the compression a small amount (both are open chambered but I bet the 340/360 chambers are a bit bigger) That trumps a little compression every time.