Quote:
Originally Posted by Camaro1973
You lose boost because barometric pressure is lower at higher altitudes. The rest about cold days, hot days is just another factor. Regardless of altitude on hot days your simply going to lose more power because of the heat.
DA factors all of that in, elevation and atmospheric conditions. Temperature, humidity and elevation are all calculated.
If you take the same car, same temps but different elevation say 6000ft to 1000ft and at 6000ft it makes 75hp less because it’s lost 3lbs of boost, if you increase the boost back to where it was at 1000ft theoretically it should make the same power. (Keyword here is same temps)
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I think you are thinking of something else when it comes to "boost". The absolute manifold pressure will be lower because the lower barometric pressure is a lower starting point. That's not the boost pressure I was talking about. I was specifically referring to the pressure increase across the blower; what most people refer to as "boost" and engineers might call gauge pressure downstream of a blower. It inversely is the pressure loss across the system (engine and exhaust). Its lower at high elevations since the mass airflow rate is lower, and thus, there's less restriction.
If you can spin the blower faster to get the mass airflow back to what it would be at a lower elevation, then yes, since the mass airflow is equal, boost would go back up, and the engine would theoretically make the same power (that requires some assumptions, though, e.g., similar blower eff.).
And as far as ambient temperature, I wasn't implying that it is only applicable at high elevations, it is of course applicable anywhere. I was pointing out where supercharging loses more than a naturally aspirated engine (due to the higher charge air temps adversely affecting timing).