Quote:
Originally Posted by footie
I bow to your better judgement on this. I honestly thought N/A engines had less variations in temperature and altitude but clearly I must be wrong in this opinion...
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The SAE says that, at a given boost level, forced induction engines gain and lose more power due to ambient temperature and humidity than normally aspirated engines do, but they lose less due to altitude (which is obvious if you think about it*). However, turbo engines now do even better at altitude because they typically compensate for altitude (up to a point) by simply dialing up the boost accordingly.
They do this by dialing into an absolute pressure maximum, rather than a boost maximum. If a given car has a boost limit of 10.3 psi at sea level (thereby giving 25 psi absolute), it will typically bump the boost to 13 psi if you are at 12 psi ambient due to altitude or if you're in the funnel of a tornado - when admittedly max boost may not be the thing foremost in your mind.
Bruce
* The reason it's obvious is that, if you lose 3psi due to altitude in a max boost system (set at 10.3 for 25 total at sea level), you're losing proportionally less than if you started at 14.7 psi and lost 3.