The Blacktop has an inside shape on the manifold in a far more of a heart shape as opposed to Silvertop’s circular inlets (see “Throttles”). The Blacktop inlets at the head side also are wider to permit with the larger inlet ports in the head. Make sure you see “Throttles”, https://4ageblacktopengineforsale48147.ampblogs.com/facts-about-blacktop-20v-4age-revealed-71308442