the combustion chamber/piston dome size is NOT and issue when putting h22 pistons into the h23 block. its a matter of compression height, the h22 has a higher compression height, stick h22 pistons in a h23 head and the sides of the piston WILL hit the head. we learned this the hard way. the h22 piston sticks out of the top of the block slightly when put in a h23 block. its not the dome that hits it the flat part on the sides that hits.