Wastegate...
Wastegates act like the floodgates at Hoover dam. When the floodgates on the dam are closed the water is forced to go through turbines to produce electricity - like your turbos producing boost. However if the turbines begin to spin too quickly or too much water backs up behind the damn the floodgates must be opened to relieve some of the pressure - same thing with your turbos.
As your turbos approach the wastegate setting, 11PSI stock, a flap begins to open allowing exhaust gas to bypass the turbos. As you reach the preset boost limit the flap opens wider to hold the boost at the preset level. Sometimes the wastegate simply cannot flow enough exhaust around the turbo and boost will still rise - that's boost creep. T-bleeders like what you've got installed will weaken the pressure signal to the wastegate allowing boost to rise higher than the preset wastegate setting.
Pulling the wastegate hose will prevent the wastegate from seeing ANY signal and boost will climb a great deal. The turbos on the Supra are apparently small enough that the turbos simply don't produce enough boost to blow the motor, at least not real quickly. The downside is that when you do this the turbos spin VERY fast - out of their design range in fact. This is "bad" for them and can lead to an early failure (ahem). Long periods of high boost like this, say on the highway, would really stress them.
Also, when the turbos spin that fast they heat the air more than they would when operating within design spec - at some point you get diminishing power returns. This is also why single turbos at the same boost level will often make more power than the twins - the air temp is cooler because th ebigger turbo is more efficient.
Oh, electronic boost controllers are better because they will prevent the wastegate form seeing ANY pressure or opening at all until the desired boost is reached, they will then cycle a solenoid very quickly or open a valve to maintain the boost level you've selected. Some manual boost controllers can also do something like this using a check valve but I've yet to try one (built one, not had time). Fuzzy logic controllers work by learning just how close to the set limit they can get (without overshooting) before opening at all. This makes them "better" so far as response goes bu tthey don't always work well in all applications. Sometimes the solenoid in an electronic controller isn't strong enough to withstand the amoount of boost you run with out leaking air past - at this point you can no longer raise the boost further, something to keep in mind in high boost apps like some Supras.
Hope that helps!
