What don’t you by calculators. There are few things to bench race about when it comes to cylinder heads making power. But to break it down to simple, the KISS method would be, cfm X 2 = possible power output and only for a hot street engine. It is reasonable accurate for the basic bench race discussion of what a hot street car or mild track car can pull off.
It is not unreasonable to say a honest 300 cfm head can make 600hp and do it without going overboard on a few things that make for race type only material and fuel. You can build a 600 hp pump gas engine. I just wouldn’t try it with a small engine, like a 340 and expect it to be a grandma smooth idle smooth running delight to drive.
