the last motor we built had 041 ( 194/150 ) 64cc heads with speed pro .100 dome pistons and .537 / .555 cam. is the pro star alum. heads with 64cc 190 intake runners 202 / 160 , and speed pro .125 dome pistons and same cam a better combo i know the pistons will help a little on the HP. i was hopping for 460 + HP with the new combo