Originally Posted by shineboy
Speed density thing?
Well if it is like my GXP (which has a 2.0 turbo direct injection like the ST) it it a pretty complex calculation having to do with air density, charge temps, amount of fuel used, fuel octane etc and then based on that it can electronically open the waste gate at the desired boost to achieve the advertised power level. Now I don't know if the ST has it but the GM DI turbos actually have a learn down feature. So basically of you put an intake and exhaust the car will detect the increased air flow and turn down the boost to get back to stock levels. It was pretty funny but when I got my car I did an intake and exhaust and before the mods it did 235 horsepower at the wheels and after it did the exact same (I'm now over the 400 mark, just have to tune it for new mods). But again this is a GM vs Ford car so I don't know if the ST has learn down but I am 95% sure the boost levels are based on the same procedure.
For a quick reference when I bought my GXP at sea level I was at 16 psi and when I got it home (Albuquerque 5000 feet ASL) it was at 21 psi. Take the ST for a romp in the mountains and the psi will go up to compensate.