These springs are designed to work in the Q series, QR series, and QRJ series blow-off valves. The supercharger spring is specifically for supercharged cars only. If you have a quick spooling turbo it can actually push the valve open briefly before the chargegets to the manifold which results in dumping boost. TiAL BOV's need a 1/4'' i.d. DIRECT source to the manifold. Smaller lines and Tee's can cause delays in response time. Spring pressures have nothing to do with boost, ONLY vacuum.