CR250 Phathead Set 2005-07 hh25005 This Phathead set fits Honda CR250 2005-07. Phathead sets are CNC machined from 6160 Billet Aluminum. They feature interchangeable domes (combustion chambers) with different compression ratios. Phathead sets include a Phathead body, your choice of two domes, o-rings, all necessary hardware and installation instructions. The standard two domes for this set are the H31 (20.5cc) the dome closest to stock, and one step higher compression H32 (19.6cc). The higher compression domes available are the H33 (18.6cc), H34 (17.4cc) and H35 (16.8cc) domes. When selecting domes, the smaller the cc the higher the compression. To order a Phathead set choose the color of head body with the drop down menu below. Enter the 2 dome sizes you want with the set. By entering no dome selection defaults to the standard set of domes. WARNING. When using the higher compression domes you must run high octane fuel. Running low octane fuel in a high compression engine could cause serious engine damage. Experienced motor builders, to view a list of additional dome options available for this head set go to the H3 series domes category COMES IN ALLOY RED BLUE BLACK AND GOLD