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Whats normal compression?

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Old May 20, 2010 | 09:54 PM
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bill11012
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Whats normal compression?

I tested my compression well doing a plug change and it was only 115-120 PSI.

What should it be on a normal, healty engine?
It seems to run great and I though it would be higher than that...
 
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Old May 21, 2010 | 06:24 AM
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That is a low number but I dont know what the v-10 should be. It is listed as 9:1 in my 2003 owners manual. On Harley compression checks that would be anywhere from 170-180. The key is to disconnect the injector, ground the plug and open the throttle body plate completely. I dont know if it is the same on the trucks. Sorry to be of little help.

Did they all measure the same? That is the important part.
 
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Old May 21, 2010 | 06:59 AM
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Bill, do you open the throttle plate while doing it, AND did you have all the other plugs out of the engine at the time?

Cam timing/duration has a lot to do with "static" compression, but you're right, I would have thought it would be higher than what you found.
 
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Old May 21, 2010 | 11:33 AM
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No, throttle was closed and most of the other plugs were in.
They did all come out the same.
 
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Old May 22, 2010 | 10:55 AM
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Originally Posted by bill11012
No, throttle was closed and most of the other plugs were in.
They did all come out the same.
Then it makes perfect sense. The throttle should be open during a compression check, just so you can compare with other compression tests or the "book".

But with it closed, as long as they all came out the same (or within 10% I think), that's PERFECT.

Sounds like you have a great long-life motor in there
 
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Old May 22, 2010 | 11:10 AM
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Originally Posted by Krewat
that's PERFECT.
Sounds like you have a great long-life motor in there
Awsome!
 
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