Compression - Altitude Calculations

[Don C]

This spreadsheet was prompted by a thread a few days ago, which made me think about something that I realized many years ago. I lived at altitudes of more than 4,000 feet, and checking manifold vacuum and compression on the cylinders always resulted in low readings. I finally realized in Physics class in high school it was a result of atmospheric pressures (or lack thereof). The attached spreadsheet is set up so that anyone can enter the altitude where they are and barometric pressure (if known), the compression readings for each cylinder, and calculate the highest compression to each cylinder percentage and the compression ratio of each cylinder. If the altitude and/or barometric pressure is unknown enter zero and the calculations default to sea level standard pressures.

This is also an easy way to play around with pressures and see how much altitude and barometric pressures change the absolute pressure, giving you an idea of how it messes with carburetor air/fuel ratios.

If anyone sees any errors or flaws, please let me know.

Compression Calculations.xlsx

Compression Calculations.xls

 

[marks73]

That is how the big money boys who race all over the country do it.