the compression ratio is not a ratio of pressure. it is a volume ratio;specifically its the cylinder+combustion chamber volume at BDC/combustion chanber+cylinder volume at TDC. The compression gauge pressure for typical gas engines on tractors is ~ C x pambient x[(compression ratio)^1.4-1] wwhere C is between 0.65 and 0.75. ).67 seems to work well on the Ferguson Continentals and the N seried Fords The compression gauge pressure should always be measured with the throttle plate fully open.
So for your 7:1 compression ratio, if the ambient pressure is 14.7 psia , your compression pressure should be ~ 140 psi.
Having said that if the manifold pressure is 20 inches Hg vacuum, that"s about 4.9 psia so the compression pressure at idle would be ~ 48 psi.
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Today's Featured Article - Diagnosing Engine Difficulty - Diesel Tractors - by Staff. The following suggestions are listed for your assistance. You can make simple adjustments on your tractor that will improve its operation and save you the time and expense of hiring someone to do it for you. Always make one adjustment at a time, and if the adjustment made does not improve the condition, return to the original setting before proceeding to the next adjustment. Hard Starting Cold air temperatures. Insufficient fuel.
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