a supercharger that makes 10psi at sea leval won't make that at higher altitudes, a turbo will still make all 10psi. If the wast gate sticks a turbo thats set up for 10 psi can make 20+(till it comes apart)... a s/c is spinning off the belt, it never changes boost...Silverback said:10 PSI will still be 10 PSI.
The difference is that there will still be less oxygen to burn, hence the loss of HP.