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Yanmar engine compression
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<blockquote data-quote="SkidRoe" data-source="post: 60388" data-attributes="member: 3290"><p>Hi k9, you were close in your calculation of static pressure. Rule of thumb atmospheric pressure is 14.7 psi (depending on your altitude). You also need to add one atmosphere to your calculation, as the starting point of the calculation is one atmosphere. With that, you have: (18 x 14.7)+14.7= 279.3 psi. As I said, this is static pressure only, not including any piston ring losses (blow-by). The one thing that this formula does not take into account at all is any of the "supercharging" effect you get from the inertia of the air rushing into the cylinder as the engine is cranked at speed. This will further increase the pressure achieved during a compression test, but is a difficult value to calculate by hand. Valve overlap, valve size, port design, intake manifold design, etc. all affect this.</p></blockquote><p></p>
[QUOTE="SkidRoe, post: 60388, member: 3290"] Hi k9, you were close in your calculation of static pressure. Rule of thumb atmospheric pressure is 14.7 psi (depending on your altitude). You also need to add one atmosphere to your calculation, as the starting point of the calculation is one atmosphere. With that, you have: (18 x 14.7)+14.7= 279.3 psi. As I said, this is static pressure only, not including any piston ring losses (blow-by). The one thing that this formula does not take into account at all is any of the "supercharging" effect you get from the inertia of the air rushing into the cylinder as the engine is cranked at speed. This will further increase the pressure achieved during a compression test, but is a difficult value to calculate by hand. Valve overlap, valve size, port design, intake manifold design, etc. all affect this. [/QUOTE]
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