The Boss Ford engines were "Semi-Hemi" design. So was the Chevy Rat motor. I've always thought the Ford would make more HP just cuz it was able to flow more air & fuel thru the heads than the Rat. I don't think they ran all that great on nitro (except maybe for Mickey Thompson cars), altho Bob Glidden sure made that engine run in Pro Stock. Seem to remember that the Mopar Hemi could only run so much compression due to the head design (gas & carbs), and the Rat & Boss engines went way beyond that just cuz they were "semi-hemi". Basically killed the Elephant in Pro Stock.