I think the real #s from the 2.9 crowlers is 1300 cfm. We run them on the PS boat, and used with the "old school" cast iron heads they' re hard to beat. With the CFM #s of later years, they are probably a little on the "light" side of the flow capabilities of the 21st century heads................I'm still planing on using them on the short stroke PS motor, with the cast iron heads, although the heads of today will find them lacking in flow............MP