Now the heads flow 259 cfm on the intake and 189 cfm through the exhaust port, both at 0.500-inch lift. Moving to 0.600-inch lift, the flow numbers increase to 269 and 195 for a gain of 16 and 6 ...

Ghoniem, 3D Vortex Simulation of Intake Flow in a Port-Cylinder with a Valve Seat and a Moving Piston, SAE Transactions, Vol. 105, Section 3: JOURNAL OF ENGINES (1996), pp. 1627-1639. Free online ...