compression range of 100 -120hp motors

[bigfork308]

In the next few mounths I plan on up sizing the motor on my boat to 100-120 range. any motor that I serouslly look at I will do a compression test.

Question is this.

I know that they should be within 10% of each other. But what range should they be in over 100psi. 90, 130 ????

I have looked everywhere and can't find anything on what range they should be in.

 

[tboltmike]

I went thru the same situation a couple of months ago. The service manual for my '75, 115 gave no numbers or mentioned compression testing and only got the spread numbers from this site and except one person hinted at 100 was good. Mine tested 80 to 70, but ran well once I cleaned the carb. The OMC local dealer said an overhaul was in my near future.

 

[Robin simmons]

I went thru the same situation a couple of months ago. The service manual for my '75, 115 gave no numbers or mentioned compression testing and only got the spread numbers from this site and except one person hinted at 100 was good. Mine tested 80 to 70, but ran well once I cleaned the carb. The OMC local dealer said an overhaul was in my near future.

So what is the compression supposed to be? Surely when he told you a rebuild was coming he told you what it was supposed to be

 

[racerone]

Should be around 130 PSI on a 75 model Johnson 115 HP.---Use a good gauge

 

[faztbullet]

Depends if you are looking at a crossflow or looper

 

[racerone]

Tested a 1990 model 100 HP Evinrude ( low hrs ) recently.-----Found 135 / 130 on compression test.