wastegates only work if your car is intercooled when you have pressure, and even then, it is only used to relieve pressure at points when it is too high. If you have an intercooler, coodoes, but with a manual tranny, as you shift, your turbo does not spin between shifts, because there is minimal exhaust for at least .5 sec (depending on driver). In that half a sec, a turbo spinning @ 4700 RPMS and say 15 lbs of boost, could drop to 2200 rpms, and 1 or 2 lbs of boost. The exhaust output is greater with an automatic because some load is always on the transmission for more exhaust to be exerted. As for a manual, as soon as you depress the clutch, the load is lifted, and the motor is no longer under any load, so the exhaust is considerably minimized, as opposed to a motor under a load.
The best example I can give you is, have you ever seen a big ass truck with too heavy of a load traveling down hill? Smoke would be pluming out of that trucks' stacks because the motor and tranny are taking all the weight, however, the second he shifts gears, the smoke stops, wether it be for a second, or even a half second, the is little or no smoke...All boost is gone. Then the truck shifts back into it, and a second later, the smoke comes billowing out again...boost builds up again, but @ a considerably lower amount. Same goes for cars, just less weight, and usually no deisel black smoke...lol...But the auto trannies are the best option for our cars as proven by most TR racers.
John