Huh, weird. 515 + 515 = 1030 so how does a 1030 kit equal a 1050? Also, an xb12 has the same bore as an xb9 but there is an obvious difference in the engine displacement. I'm just trying to understand how it's possible for different cc kits to be the same. Also the blast kit is made for the blast head which is different than the xb head which is what I'm using. The xb9 piston is done shaped, higher compression than the blast but the blast has the same bore and stroke as the xb9 but uses a flat piston which is where is loses compression but keeps the cc and also it is exactly half the cc displacement of the xb9