Even though the Blacktop head incorporates a a lot more open combustion chamber (see “Head combustion- chambers”) it nevertheless has a greater static compression ratio (see “compression ratio”), this is purely because of the piston structure. The Silvertop piston incorporates a very compact dome with two deeply angled exhaust flycuts, https://4age-20v-blacktop-for-sal70234.newbigblog.com/37398810/what-does-blacktop-20v-4age-mean