On a root blower like the GT500 ... Our on a blower period? Because my friend zo6 has a centrifugal Vortec blower and he has a waste gate. He also has a knob that allows to change the amount of boost.
If you have a blower, and you loose boost/perf with altitude, then it's a piss poor design that doesn't take into account the advantages of force induction over NA. 
Install your pulley that can actually give you 10 psi at max rpm and regulate the blow off valve to give you your 8 psi max. So when you drag race in Denver you still have your 8 psi. Now that would make sense to me. 
There's + and -'s with blower designs. Centrifigal has the advanatage of greater boost potential and control due to a wastegate, so you can actually spin it up for more boost then you actually need and the excess can be vented. It's drawback is that it's not as instantaneous boost as a positive displacement, and requires a lot more piping and engine compartment space. For all practical purposes it's a belt driven turbocharger. Positive displacement blowers are boost controlled over their pulley size, and all of them have an efficiency range (eg. spinning them beyond a certain point doesn't get you much except heat). So you can't set it to give you 10psi boost in Denver and then drive to Louisiana and it still only have 10psi of boost, will be quite a bit more. The opposite true in the other direction. You would have to pulley up or down to keep the boost consistent in a positive displacement, keeping in mind the blowers operating RPM range. One other reason you tend to see positive's at lower boost levels is becouse of the difficulty of intercooling them effectively. Since Boost is built right on top of the engine you only have so much room to cool off the boosted air in. While a centrifigal can run huge intercoolers and lots of piping to help cool the air in, since boost is built well before the engine. Given this, you may thing why would anyone want a positive over a centrifigal? two main reasons and why the OE tends to stick with them. They tend to be a smaller package with less piping and engine space taken, and secondly boost is pretty much instant. They make brutal torque down low, which makes them fun around town. If you want to make big power, centrifigal is the way to go. Almost every boosted car I see over 600 RWHP (that's over 700 engine) is either running a centrifigal or turbo, in large part due to intercooling issues on the positives. Can't run big boost numbers with high intake air temps or your engine isn't long for this world. At 533RWHP my PD blower engine ran into the intake air heat issue and timing had to be kept very timid. So I'm leaving a lot on the table due to heat that I wouldn't have to with a centrifigal with a large intercooler. The alcohol injection helped quite a bit later on when I added it last year, but even then I have to add the alky before the blower so I can't inject too much. I just wanted to get over that 550 mark anyway with my stock bottom end
BigRat
