I am trying to determine the proper compression for my yanmar 40HP diesel engine. My Yanmar factory service manual says the compression is "18.0". I assume that is 18:1 ratio. I see someplaces on the internet that give different formulas for turning this in PSI. One of the simple to understand says to multiply a factor of 14.2 x ratio value. That comes out to 255 PSI compression on my engine. That seems almost too low of a value in itself. I seem to find some consistency that suggests that diesels need at least 300 psi to start. I paid someone to do a compression test on my engine and he said I have 190 psi. but that is a cold engine. I cannot comprehend if the data is meaningful, since the engine should be warm for a compression check so you can guesstimate the ring status. Question... can anyone confirm I have the correct formula for determining my compression value I am looking for. As we all know, if it is on the internet, it has to be true. Thanks Ken