What people are referring to is how much boost they are running and at what elevation they are doing it at. THis gives everyone reading, an idea of how roughly how much power they are making, what kind of fuel needs to be run, etc. For instance, I am running 12 PSI of boost at 10K feet. I have to set up my clutching and figure out how much race/avgas is needed to safely run that level of boost. Someone at 2500' above sea level, would be making a LOT more power than me at the same 12 PSI of boost, and therefore would have to clutch differently, and run a bunch more octane in there fuel, to safely do this. For instance, lets say your '11 Pro makes 145 HP stock, at sea level. Because of atmospheric pressure, if you were to come out here at 10K feet, that number would drastically decrease. If you were to add a turbo, and run 5 PSI (at 10K'), your sled would be producing ROUGHLY, the stock, sea level HP. Your turbo will make boost at any elevation, but will equate to much different total HP, depending where you are in elevation. I hope that explains it and helps.
