Compression question

[jbusch]

Alright guys, time to settle a debate. I have an 18 m8000 with 1800 miles on it and I live at 5300ft in Colorado. Its for sale and I have a guy that's interested in buying from sea-level. He asked that I do a compression test. My tester shows 120psi in both cylinders. He thinks I should be showing 140psi. What should it be? And is there a different between altitude and sea-level?
My dealer says 120psi is spot on here. His dealer says should be 140 to 145psi.

Thoughts?

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[Ol* Geezer]

Higher elevations will show lower psi as there is less atmospheric pressure available. 120 psi at 5300 ft is good.

 

[Motorbreath_]

Compression testing at elevation.

For example: Specified compression = 150psi, Altitude = 2000ft, (150 x .943 = 141.5psi expected@2000ft)

Altitude (ft)	Correction Factor		Altitude (ft)	Correction Factor
500	.987		3500	.907
1000	.971		4000	.888
1500	.960		4500	.880
2000	.943		5000	.862
2500	.933		5500	.853
3000	.915		6000	.836

 

[Old & slow]

Real life test for me was 145 at 2000 ft and 120 at 7000 ft same tester. Give or take a few feet on both numbers. The more important number is if they are equal between holes, testers will vary along with the elevation.
edit this was not a factory head and not from a C-Tec just an example of elevation difference.

 

[JMCX]

I live at 3400' and do regular compression tests on my 19 just to keep an eye on things. Have since new. I've never seen 120#. Always in the teens.

 

[kanedog]

300ft-125lbs

 

[Vern]

I live at around 4500ft, I’ve never checked my ctec, but the highest I remember ever seeing on a sled at my house is like 128 on a sled that had a recut head. I agree with the others, 120 is normal at your elevation.

 

[Goinboardin]

110 psi on mine at 7200'.

 

[Coldfinger]

Digit9 on youtube has a good video. Compression Testing A Snowmobile.

 

[Rick E]

Keep in mind that these are static cylinder pressure readings.
And yes, I agree that various altitudes will give us different static cylinder pressure readings.

It is also important to note that each cylinder gave the same reading.

 

[madmax]

Both my 18’ and 19’ cats are just over 120lbs in Salt Lake City, 5000 feet

 

[JMCX]

Also keep in mind that your and everyone else's $5 HF compression tester can give less than precision readings.

 

[kanedog]

Also keep in mind that your and everyone else's $5 HF compression tester can give less than precision readings.

Mine was $8. I guess I got ripped off!