My statement is based on 1 SM factory CNC head that I purchased last year on Black Friday. In my opinion (which could be wrong), that one head had a throat that was way to large at 93% and a port volume that was a little too large for the 265-270 cfm that it flowed. It had a 2.02 valve. To get the throat to a more reasonable 90-90.5%, a 2.08 valve would need to be used. My guess is that a good 2.08 valve job on that head would get the flow into the 280s with little other work. That should put the port velocity into a little better range as well. I do not know if all SM CNC heads had the same specs as mine.