What I figured out along time ago is this: If a SBC head flows 220 cfm the cylinder may only "see" and use 199 cfm. A SBM head that flows 219 cfm will see and use 210 cfm. This is due to the valve angle 23* vs 18* . This is also why a SBC will respond to angle milling better than a SBM. It's also why a BBM responds to angle milling and a dowel shift BIGTIME. J.Rob
