Despite the fact that the Blacktop head includes a far more open combustion chamber (see “Head combustion- chambers”) it however has a better static compression ratio (see “compression ratio”), this is only due to piston structure. The Silvertop piston incorporates a pretty modest dome with two deeply angled exhaust flycuts, https://simonrstqo.blogoscience.com/34919981/what-does-toyota-4age-for-sale-mean