[Craig Hendrickson]

H-O used both a wastegate and a blow-off valve on the TurboForce, but not at the same time and not always.

A wastegate is on the inlet side (between exhaust manifolds and turbo exhaust scroll). It bleeds off exhaust flow and pressure to control the boost indirectly. A wastegate lives in a hot environment being attached to an exhaust pipe somewhere. We usually ran them without an outlet pipe and muffler; you can definitely hear the "whoosh" when it opens up.

A blow-off valve is on the outlet side (between turbo outlet scroll and the pressure hat). It opens when the boost pressure exceeds its setting so it controls the boost directly. A blow-off valve lives in a more benign environment than a wastegate and is more effective on controlling the boost into the carburetor when you go from WOT to throttles closed quickly. However, a blow-off valve potentially lets the turbo overspeed and therefore operate further away from the sweet spot island on the turbo map.

Even though the wastegate is a little more expensive, that's what I would recommend. As a matter of fact, the earlier versions of the TurboForce pressure hat had a pad cast in the side which could be machined for mounting a blow-off valve. The final and best version of the pressure hat had eliminated that pad.

Craig