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davey w

What Compression

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Thought this was a good topic read it in hot boat,260 merc should be right at 150psi,The main thing is that they are even as compression numbers can be different for several reasons and they are mainly the gauge itself, RPM the engine is cranking while taking the readings, elevation and atmospheric conditions. The 150 reading is on my gauge is cracking atleast 250 RPM near sea level. Addtionally these numbers are about maximum runing pump 91-octane gasoline. Better way to check an engines condition is to run a leak odwn test. This is a test that determines the amount of ear leaking by the rings. Gauges measure the amount of air supplied to the top of the piston with the porch shut and what escapes by the rings.

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Very true that a leakdown test is better to check engine condition, but I always do both and keep records & dates of each test. I live at 1300ft elevation and that's a 5psi drop per cylinder over someone near sea-level.

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