The Blacktop has an inner form from the manifold in a more of a heart shape compared to the Silvertop’s round inlets (see “Throttles”). The Blacktop inlets at the head side can also be broader to permit for the larger sized inlet ports in the head. Be sure to see https://ricardonfsnz.blogdosaga.com/34523270/the-best-side-of-4age-20v-itbs