There are several ways to run gate control solenoids or pressure valves. In a car that is not a strip-only car, you really want to run a spring and just use the dome pressure (or leak off compressor sample pressure) to increase boost above the spring. Dual valves are always more stable unless it is a straight compressor sample bleed system (which often is not that stable anyway) where you just bleed off some compressor boost reference sample to trick the waste gate.
Waste gates tend to leak before reaching opening pressure. Simply bleeding the compressor sample signal off to atmosphere might not work so well, because the exhaust pressure can push the gate open and not give a stable boost pressure.
If you use CO2 (or some other pressure source), you can force the waste gate closed to seal the wastegate tight. The CO2 just augments the spring. With CO2, the system uses less CO2 and has much better control with a dual valve system, where one valve adds dome pressure and the other bleeds it off.
I use CO2 with dual solenoids (bleed and charge) to the dome and a 12 psi spring. That way I can dial any boost I like over 12 psi. It goes a long time on a bottle at the track. I've gone almost a season now and still have almost full CO2 pressure.
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89 LX. 363, single turbo, Super Vic EFI, TFS high port heads by TEA, solid roller, glide. Holley HP EFI. (exact combo varies)