210 PSI Compression Test

[ajkolar]

I changed my spark plugs today as a yearly maint. item and decided while I had the plugs out I would check my compression. Results as follows:<br /><br />1 - 210<br />2 - 210<br />3 - 210<br />4 - 215<br />5 - 215<br />6 - 215<br />7 - 210<br />8 - 210<br /><br />Doesn't this seem high? This is a 1 year old motor (rebuild) and I know he said he (Raul at Rapid-O-marine) was going to put flat top pistons in it, so I am sure that would cause a slightly higher compression, but does 210 sound right? The last motor I took out was more around 140-150 psi. Thanks!

 

[Haut Medoc]

Re: 210 PSI Compression Test

Did you have the throttle wide open?....JK

 

[ajkolar]

Re: 210 PSI Compression Test

No I believe the throttle was at idle or fast idle position.

 

[3car]

Re: 210 PSI Compression Test

I bought a 4.3 S-10 motor w/ 25,000 miles on it, and the compression was between 190- 205 on all 6.

 

[Bondo]

Re: 210 PSI Compression Test

I'd say she's Pretty Healthy,.........

 

[KaGee]

Re: 210 PSI Compression Test

Boy AJ, them spark plug Mfg's really love guys like you! Only one season?

 

[ajkolar]

Re: 210 PSI Compression Test

I do not plan to change them every season, but I wanted to switch to the ones recommeneded in the service manual, especially after reading Bondo's appreciation of the MR45T. <br /><br />So no concerns about 210-215 psi in the cylinders of a 5.7 SBC, then? That is good news! I guess the jump from 150 in the old motor to 210 in the new one scared me for a second. Thanks!

 

[Bondo]

Re: 210 PSI Compression Test

That's MR43T.....Not 45

 

[ajkolar]

Re: 210 PSI Compression Test

Sorry, dang fat fingers! MR43T is what I put in and it idles real nice

 

[ron7000]

Re: 210 PSI Compression Test

Originally posted by ajkolar:<br /> was going to put flat top pistons in it, so I am sure that would cause a slightly higher compression, but does 210 sound right? The last motor I took out was more around 140-150 psi. Thanks!

average static compression #'s are usually anywhere from 150-180 psi. There are a lot of other things that influence the amount of compression when the engine is running so this measurement doesn't mean all that much. The good news would be a 200+ psi reading means you are definitely getting good compression.<br />What may have happened is the rebuilder used a thinner head gasket and/or had the heads and/or block decked which can increase compression. And of course the pistons have a large impact on measurable compression too.<br />If you've run this motor a few hours and haven't noticed pinging or had the valves meet the pistons at high rpms then you don't have anything to worry about. <br />Do you trust your compression gauge? Use a couple others and find out what they report.

 

[3car]

Re: 210 PSI Compression Test

I just did a compression check of my own.<br /><br />220<br />220<br />220<br />210<br />200<br /> 60<br /><br />