The intake manifold of the S197 has a second set of butterflies in them, placed just before the intake valve. The goal of these plates is to increase the velocity of the air as it moves into the combustion chamber. Increasing the velocity of the air as it enters (also called port velocity) helps the engine build torque and maintain fuel efficiency. In Theory, as the engine speed increases, these butterflies are supposed to open (between 1500 and 3000 RPMS based on engine load) and allow the air into the cylinder without restriction. In function however, these plates do still end up providing some small restriction to the intake. As their name implies, the CMCV Deletes remove these butterflies completely.