Maybe I should re-read the entire thread, but I'll take a guess at the confusion [though I think was discussed before].
At sea level, you only have roughly 30"Hg [14.7psi]. At 30000ft, you only have about 20%, in other words the air will be much less dense, so the naturally aspirated engine will not get the same internal pressures and temperatures for optimal combustion.
I think everyone follows that, but where it becomes confusion: at some point [I think also mentioned earlier] a given engine; espcially diesel with no spark to initiate combustion, simply will not run. Until then, it will have less and less performance. This will be slightly different for each engine. Also, neither the pressure curve, nor [I guessing here] the engine response to it is a truely linear; in other words there is no simple factor to multiply and get the correction. However [again, I'm guessing], each manufacture likely takes their performance data, selects a range [maybe 0 to 10K ft; maybe 5K; maybe 15K], and makes a close approximation for a correction factor.
For the purposes here, knowing that there is a loss and knowing that a charger will make up most of it is likely the important thing [can't beat the ol at home testing either!]. Then whether you choose a 3 or 4% correction, well trust the manufacture info or your gut is the best I can think of.
Uh....clear as mud....and I was trying to clarify. /forums/images/graemlins/confused.gif Well, maybe, others read my babble as more informative than I do. /forums/images/graemlins/smile.gif
