In what way are pistons used for hemi engines different than the pistons used for non-hemi engines? twice as many pistons are required for a hemi engine than a non-hemi engine due its increased need to generate power. the piston used for a hemi features a dome-shaped head rather than a flat head. the piston for a hemi has 6 compression rings, whereas there are normally only 2 for a non-hemi engine. the piston is oval-shaped for a hemi, but is perfectly round in a non-hemi.