I was up at my cabin this weekend cutting up some old slash and burning it since there was 10 inches of fresh snow on the ground, I thought about that claim of 3% loss with each 1000 feet of elevation gain, since I was at 10k. I was using my stihl 361 and it was tuned for slight 4 stroking out of the cut and it cleaned up in the cut, I don't know if it would have 40% more power at sea level, but I doubt it.
I'm sure this was done is a laboratory type setting where they can hold the fuel and air constant and measure power. Well, that's fine in a lab setting where all the factors can be fixed, but in real life we don't get fixed variables.
Take the auto tune or Mtronic saws for example. The engineers want the fuel/air mixture to equal 14.7, that is the optimal burn mixture. They obtain this by measuring the volume of air coming through the carb and adjust the fuel (richen or lean) to make the ratio = 14.7. The solenoid in the carb continually adjust the fuel to keep the saw in the proper operating range. This is all regardless of altitude as they claim they can adjust for altitude changes. Also Notice that they are not measuring the density of air, only the volume. That is a very important thing to consider when thinking this through.
So a person that can tune a saw for their conditions is just like an auto tune saw and can still get the proper staticometric fuel / air ratio.
