Many different head shapes (hemisphere, double bouble, turbo, cone, & trumphet); different head volumes; different squish band angles; different squish clearances; different water cooling setups; different plug types; & different plug depths, have been extensively dyno tested. The cone shaped head (very narrow squish band) & the hemi shaped head (1 deg squish angle), both at .000 to.001 deck clearance make the most HP.
