i don't know the cfm but at 2500 rpm it's not much. I think bart is on the right track i just hate to completely cover up the engine. There has to be a reason for the cooling problem always with #4 cylinder. I have had my sensors on all cylinders and none have the high temp that the # 4 cyl does. It just seems to me there is something more than air flow causing this. Casey's boat runs the same as mine but doesn' over heat. We put my cht gauge on his engine when he first built it to verify it. He ran it as hard as i run mine and it never got to 450. And i have read others with this engine doesn't have the problem either. If all else fails i've got another complete engine to try. Let us know what you come up with.