Long story but, after hundreds of flow tests (self-taught) they were in the 370 range by .750". There are a few good CNC programs for them now. But flow isn't everything. (I learned to leave high HP headwork to a professional LOL.) (IMO) These heads were released in a time when there weren't many options available for BBM and their straight exit spark plug really dampens their marketablity. One addl. thing I might add is the existing pistons may need valve pocket work for radial clearence. I don't consider them an easy, practical, or economical 'bolt-on' upgrade considering what is available now.