Okay I think I might need help, but thats an entirely different subject. I am just getting my overhauled IO550 on a new to me plane reinstalled. I am reviewing brake in procedure and after 25 hours the possibility of running LOP with my GAMI injectors. Part of doing this safely is being able to identify power settings as a percent i.e 65 or 75%. I don't have a manual for this engine that gives MP's and RPM for pressure altitudes to produce desire % of power.

Does anyone have an easy method for calculating this information.

Don't know if you are updating your engine analyzer, or considering it, but EI's CGR-30P shows you your instantaneous % Hp. I presume their -50 model does also. It's a great instrument. I appreciated it during the break-in of my current engine, when it was factory-new.

-DP

In a normally aspirated engine, I use the following formulae to help me estimate % power.

RICH of PEAK
((Cruise RPM/Max RPM) * (Cruise MP/29)) x 100 = % Power

Example: At cruise at 23 squared.
((2300/2700) * (23/29)) x 100 = 68%


--------------------------------------
LEAN of PEAK
((14.9 x fuel flow)/Max HP) x 100 = % Power

Example: When 25-50 deg LOP. FF = 12 GPH.
((14.9 x 12)/300) x 100 = 60%


Good luck.

I think that is the first time I have ever seen that formula. Good info.

Flying Dave wrote:I think that is the first time I have ever seen that formula. Good info.

X2

Squash wrote:In a normally aspirated engine, I use the following formulae to help me estimate % power.

RICH of PEAK
((Cruise RPM/Max RPM) * (Cruise MP/29)) x 100 = % Power

Example: At cruise at 23 squared.
((2300/2700) * (23/29)) x 100 = 68%


--------------------------------------
LEAN of PEAK
((14.9 x fuel flow)/Max HP) x 100 = % Power

Example: When 25-50 deg LOP. FF = 12 GPH.
((14.9 x 12)/300) x 100 = 60%


Good luck.

Thanks for these formulas! After some thinking the other day I came up with the same formula that uses manifold pressure and RPM, I unfortunately had I significant back ground in chemistry (which is really just math) in college and this seemed to make sense. I guess I just felt as if pressure altitude should play a role.


Also does the constant 14.9 represent a "standard atmosphere"? If so why not 14.7psi?

mainewoodsstol wrote:
Also does the constant 14.9 represent a "standard atmosphere"? If so why not 14.7psi?

No, the 14.9 does not represent atmospheric pressure; hence not 14.7. It is a LOP conversion factor that is used for NA engines with a compression of 8.5:1 to convert fuel flow to HP.