There needs to be a big asterisk beside that 308 number. As I mentioned early on, I have used all the cheat tactics that I could come up with to get that number. For instance, the combustion chamber has clay covering the spark plug and sometimes covering the whole exhaust valve. This creates a top angle 'cone' around the valve that adds a few cfm. I have tried to optimize my port entry plate for a good smooth radius. The guide boss in the port has clay in front and behind. So honestly it's more like a 295 cfm port. And it's easier to get a port that peaks at 295 at 0.600 lift then drops off (like mine) than it is to get a port that peaks at 295 at 0.900 lift with no stall or back up. It has taken PBR a whole lot of effort to get the ports he does. I'm on flow test 580 something and haven't figured it out yet.