All it is the cylinder heads and not the engine its self. The biggest disadvantage for the Hemi design is it can only have 2 valves per cylinder. Because of this disadvantage, Top fuel dragsters use intake valves the size of your fist. 4 valves potentially can make a lot more power than just 2.
Its in the Top fuel dragsters rule book that all engines must have hemi spherical combustion chambers.[/QUOTE
if i am not mistaken the new hemi's do have 4 vales per cly and they do have 4 valves per cly in the top fuel racing .in the 50's to the 80's it was most cars had 2 valves per cly also the only engine that was banned from nascar was the ford 427 sohc cammer engine it was banned before it reach the track ,the mopar hemi had a handicap put on them so they withdrawl , the so call 427 gm mystery engine "less than 50 mystery were poduduced before Gm ban on corporate-racing was annonced in jan 1963the gm was banned from racing by gm not nascar ,the gm 427 was a wedge engine with canted valves and did not have a dome combustion chamber now back to the hemi gun i will past on it , to rich for my blood , i'll stick with my cheap norks