Colyn,

Attached is the spreadsheet modified for use with a turbocharged engine.  All I did was fix the horsepower at the sea level value.  However, I think there will be some degradation at altitude, mostly because the aftercooler isn't 100% effective.  It should still be reasonably close.  Other than that, all you do is change the takeoff speed to what you think is correct and, of course, the weight.  One could change the aerodynamic drag, but it isn't a large factor.  The drag of the IV would drop because of the smaller wing area, but would rise because of the gea configuration.  I'm not sure which is dominant, b ut at low speed it doesn't matter.  The higher wing loading mostly results in a higher takeoff speed - I don't compensate for the increased induced drag.  Perhaps I should.

 

Playing around with the spreadsheet highlighted to me one possible reason there are recurring high elevation takeoff accidents.  On my ES the calculated takeoff distance at sea level, 59F, is 1450 feet.  At 1,000 feet it increases just 130 feet - hardly enough to even notice.  However, increase the pressure altitude from 7,000 to 8,000 at the same 59F and the distance increases from 3200 to 3600 feet - a whopping 400 feet increase.