The BBV opens up after a certain psi. Most twincharge setups are already hitting 11's before they add the turbo. When they do, they switch to a larger pulley on the s/c so that it doesnt rob the power by spinning the rotors that fast. It only is used to bring the boost up faster, no turbo lag. After that the turbo takes over. A single turbo only solution would have your turbo lag. You'd think that a few hp would be robbed by the inlet air/boost being limited to the bbv opening and blowing through the rotor packs, but maybe the tradeoff is worth it. ZZP claims that it will always outperform a turbo only setup, but nobody has really tested this accurately that I know of.