Since I live above 6500' and we have a new "just supercharge it" guy I have a relevant question.  When a Turboed/Supercharged engine is running at say 10psi is that psi relative or absolute? Basically here at 6500' the ambient air pressure is significantly less than at sea level, so is this 10psi above the current atmospheric pressure (relative) or is it absolute so the car runs the same regardless of outside airpressure (the intake has the same psi in it rather the engine is at sea level or 6500')?

It's relative, in that at 6500' you are shoving in 10lb. of mixture that is way thinner than 10 lb. of mixture at 1000'.

 It would still be a kick in the ass though.

Thanks, it is important to know because I regularly drive to places around sea level which would mean a boost adjustment is necessary if I crank it up up here in the thin air I'd have to turn it down before the trip to keep from over boosting the engine.   

Yeah, with belt-driven blowers it's always relative to atomspheric.  Turbo guys have tricks they can use to make it relative to absolute absolute, although even then it's not easy.  The old Lotus Esprit turbo 4 motor had a turbo system that was somehow made to boost relative to a constant pressure regardless of altitude making engine output, theoretically, the same regardless of altitude.