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When ROP, there is excess fuel and so HP is related to MAP (since MAP is throttle opening which is amount of air being provided to the available fuel), with unused fuel going out the exhaust manifold (and increases EGTs). So the amount of air limits the amount of energy extracted from the fuel.
When LOP, the fuel is limited (and air is relatively plentiful), and so fuel flow defines the available energy available to drive the engine cylinders. Fuel flow x conversion factor equals HP when LOP. Whether the conversion factor is 14.7, or 13.7 hp/gph (as I've been told for my TSIO-55E), the MAP is simply providing excess air at higher settings; the mixture is even more LOP. Cooler air goes out the exhaust manifold, flame extinguished
Recall that when you add MAP, the fuel flow increases. If you set 17.5gph at MAP 30" (what you call 73.5% power at 14.7 conversion factor), and you then increase MAP to 32" the fuel flow will increase to (best guess) 18.2gph, a higher power output. If you then pull the red knob some more, lowering the fuel flow back to 17.5gph, moving further LOP successfully (without cough or complaint), then you are rendering the SAME power output as the lower MAP but same fuel flow. You are correct in your supposition below, but how you got there was not so simplistic as just changing one setting (MAP).
Higher MAP is a tremendous source of heat, and so higher MAP generates more engine heat and higher CHTs. If you can operate your pressurization system adequately at the lowest MAP suitable to the flight (lowest compression heat delivered to each cylinder), and lean somewhere LOP to get the desired HP output for your budget or speed, you have reached Nirvana.
Jeff L
LIVP (LOP by 500' AGL)
PS My qualifications: I stayed at a Holiday Inn.
My ES-P has a TSIO-550E with GAMI injectors, and i've recently been through advancedpilot's web LOP course. But I'm still unclear on at least one point.
My TSIO-550E will happily run at 17.5 GPH at a MP of any of 30, 31, 32 (among others). All cylinders remain below 380, and TIT is reasonable.
My understanding is multiplying 14.7 x GPH yields HP, in this case 73.5% power
Is it 73% power no matter how I set the MP, so long as temperatures remain in control? If that's true, why would I select one MP over another (realizing I can't run wide open throttle)?
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