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.
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.