I have a 1974 P337 with air conditioning, Horton STOL, no wing de-ice boots, and the Riley intercoolers. I mention all these things because each impacts performance, though none of the mods actually say how much they impact performance!
I used to use 33"/2500RPM at 17,500 and obtain about 202kts on 34GPH (204pph). Lately, I've been at 31"/2500RPM at 17,500 and obtain 196kts on 26.6gph (160pph). Note that this is "slower than book", but "book" doesn't account for the STOL kit or the air conditioning scoops (or the intercooler scoop/venturi).
My POH calls the 33"/2500 "75% power", but calls for 80pph per engine (13.3gph), which I cannot obtain without overheating the engine.
The Riley STC instructs to reduce MP by an amount between 0" and 2" depending on altitude, and it's essentially a straight line with 0" at sea level and 2" at FL200.
So my theory is that if I run 33"/2500 at 17,500', I'm at more like 85% power, based on fuel stoichiometry. Reducing MP down to 31" brings fuel usage back in line with book, implying a return to 75% power. And of course, temperatures are much easier to control.
QUESTION: Nothing about the intercooler installation should increase the rated power output of the engine, should it? Sure, the engine will produce more power if I let it, but presumably the main everyday benefit of the intercooler is better thermal control (if MP is reduced to account for the colder/denser air bring introduced into the engine). A secondary benefit is that in emergencies, slightly more power than stock, is available. Does this sound like a good way to think about aftermarket intercoolers?
BTW, my rear engine actually runs cooler than my front engine. But during climb out on hot summer days (33"/2500rpm/140mph/cowl-flaps-open/full rich), I still have to watch the temperatures on both engines.
Thanks -- Dan
Quote:
Originally Posted by SkyKing
Richard,
Typical power settings, fuel flow in PPH, TAS (Knots) and Servo Inlet Temp:
10,000 @ 75% = 33" Hg @ 2400 RPM, 88 PPH, 195 Kts & 57 F
10,000 @ 65% = 30" Hg @ 2400 RPM, 76 PPH, 184 Kts & 52 F
10,000 @ 55% = 27" Hg @ 2300 RPM, 64 PPH, 170 Kts & 46 F
16,000 @ 75% = 33" Hg @ 2400 RPM, 88 PPH, 210 Kts & 65 F
16,000 @ 65% = 30" Hg @ 2400 RPM, 76 PPH, 198 Kts & 56 F
16,000 @ 55% = 26" Hg @ 2400 RPM, 64 PPH, 182 Kts & 48 F
SkyKing
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