IO-360A and O-360 Power Spreadsheets

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I was away from home over the Christmas period, and I couldn't work on the project, so I found some time to produce a spreadsheet to calculate the power output of the Lycoming IO-360. The Excel 4 spreadsheet basically replicates the graphical power chart found in the Lycoming Operator Manual for the IO-360-A, -C, -D, -J, -K and AIO-360 series. The zipped spreadsheet can be found at this link.

Note - I found several errors in the original version of this spreadsheet that cause it to fail at lower rpm conditions. There are also data errors for 2000 and 2100 rpm. I posted a corrected version a few minutes ago, at the same link. The corrected version can be identified by the version history info in the spreadsheet. The original version has no version history info in it.

I tried comparing the spreadsheet calculations to data from the POH for a 1977 Mooney 201 with a IO-360-A3B6 engine. However it quickly became clear that the data in the Mooney POH differs significantly from the Lycoming power chart. For example, at 8000 ft and 2700 rpm, Mooney claims that 23.6" manifold pressure gives 75% power, while the Lycoming power chart gives something like 21" for 75%. Either Mooney wanted to cruise at artificially high power to give good marketing numbers, or they measure manifold pressure differently than Lycoming or Lycoming has changed their power chart since 1977.

The accuracy of the spreadsheet calculations were validated by spot checks against the power chart from a Cessna 177RG POH (IO-360-A1B6D). The spreadsheet typically calculated one-half to one percent higher power for the same rpm and MP than was given in the POH. But, the spreadsheet is valid at maximum power mixture, and the POH data is for recommended lean mixture, so this is probably about correct.

The O-360 power spreadsheet that I created several years ago is still available at this link.

I have had several requests to do a 160 hp O-320 power spreadsheet. Someday when I am on the road and looking for something to do I will do one. When I am home I prefer to use my time building.