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P-Ponk engines and JPI engine monitor constants

windknot54

MEMBER
Bend, OR
When installed my new 0-470-50, I added a JPI EDM-830 engine monitor. The EDM-830 calculates percent horsepower based on the MAP, RPM, altitude, and OAT.

During the setup process, you need to enter a couple of constants that the EDM-830 uses to calculate the percent horsepower (%HP). Of particular interest are: 1) the engine horsepower (hp); and 2) the ‘horsepower constant’ (HPC).

Lacking the results of a dynamometer test, the choice of the horsepower value for the 0-470-50 could be a bit subjective. The P-Ponk STC states 235 hp; Steve Knopp claims between 265 hp and 275 hp. I had a discussion with the JPI technical representative about the significance of this value, but I never received a satisfactory (or comprehendible) answer.

The horsepower constant has a clear and obvious impact on the %HP. For any particular power setting: increase the value of the HPC and the %HP increases, decrease the value of the HPC and the %HP decreases.

I asked the Knopps for information they might have on the 0-470-50 performance at altitude. Their response was that they believed the engine performed similarly to the IO-520-A, which has the same bore and stroke, and compression ratio. So, I have been working with the attached IO-520-A performance chart from Continental.

I’ve been flying around at various power settings and testing out the effects of the various constants. I can't fly lower than 5,000 around my place, so my testing has been at 5,000' and 7,500'. After all my experimenting, I have ended up using hp=275 and HPC=126 – a least for the moment.

I know many of you will be saying – “What’s the point? It’s all meaningless”. You’re probably right, but I’m an engineer and I love this stuff.

I would be interested in hearing anyone else’s choices on these constants and your experience.


I0-520-A performance curves.jpg
 

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Percent-of-power gauge:

$ - $$ - $$$ - $WOW!

THis is applicable to the fuel flow gauge also.
 
Since you do not know the horsepower, can you back into your question by comparing the specific fuel consumption to the fuel flow with the resultant answer being your horsepower? Isn't there an engineering calculation for this approach?
 
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