Just like upgraded intake manifolds and larger throttle body’s that are more efficient.. S&B air box is slightly larger and more efficient than stock box with a flat air filter .. getting air to the intake manifold is a important factor.. we’ve picked up has much 10/20 hp on the dyno just by playing around with different filters .. I’m not saying I achieved that with this air box, but I did see some improvement.. and I like the way it sounds