The JET Performance Powr-Flo Spacer's bore is designed to increase the velocity of the air flow into the intake manifold. By delivering the air with more velocity, it allows more air into the combustion chamber for a denser air charge. The design results in improved throttle response and impressive power gains in the mid range and top end. In addition, the increased air flow results in improved overall fuel efficiency. Simple, bolt-on installation. Precision machined out of billet aluminum by JET's in house CNC machine shop.