i have a 421 in 4mm 115mm longrod with blaster pistons. i have 17cc domes and have 210-215 compression. i think is to high. does anyone have compression readings with 18cc and 19cc domes. my alttude is about 1000 above sea level. i dont know what i need and where to buy at. i was looking for about 180-190 compression. please help thanks