Ok since I no longer have access to a ProMaxx Head I went back to my pictures that I posted in my Edelbrock to ProMaxx comparison post. Hard to really tell from pictures but it looks like the ProMaxx heads had a 3 angle valve job compared to a two for Speedmaster. Not sure way they would cut a cost corner there because there is zero labor costs involved in the two. ProMaxx heads also have some cfm gaining attention to detail in the valve seat installation as it looks like the were flapper wheel sanded and cleaned up a lot nicer after being pressed in. Athe shortside was nicely blended instead of stepped. If I were a betting man these will be in the 248-258 cfm area max. The valve job sucks but I’m still sticking with it will flow better than an Edelbrock