need typical compression #???????
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Postmaster
Joined: Mar 2008
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From: Des Moines, Iowa
need typical compression #???????
hey guys I am going to look at a 1986 4.9L 300 I6 and need the regular compression rating for the engine??? I wanted to make sure the engine was still good before i pluck it... What would be the acceptable number range for cylinder compression????
I've heard 150-160psi??? does this seam right to everyone else???
I've heard 150-160psi??? does this seam right to everyone else???
Lead Driver
Joined: Jul 2009
Posts: 6,477
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From: Sheffield, AL
I am responding quickly in the event that you are soon to look at the engine.
Others will give a more definitive answer, but yes, what you have heard is good. I've seen members list as low as 125-135 psi and still running. The most important factor is that all are within close range to each other. There is a factor such as within a certain percentage [10 or 15% maximum???).
Others will give a more definitive answer, but yes, what you have heard is good. I've seen members list as low as 125-135 psi and still running. The most important factor is that all are within close range to each other. There is a factor such as within a certain percentage [10 or 15% maximum???).
Moderator
Joined: Dec 2007
Posts: 7,987
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From: Boise, Idaho
Yup, 150 - 160 is very reasonable, and still a fresh, healthy motor.
180 is usually BRAND new with tight work done, and 120 is where its' starting to get weak.
It's when there's a variation that you really need to be concerned, such as one cylinder that's 130 and one that's 150. I think 12% variation is about the max you want to deal with.
180 is usually BRAND new with tight work done, and 120 is where its' starting to get weak.
It's when there's a variation that you really need to be concerned, such as one cylinder that's 130 and one that's 150. I think 12% variation is about the max you want to deal with.
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