Compression Test #'s
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Tuned
Joined: Jun 2017
Posts: 279
Likes: 91
From: Indiana
Compression Test #'s
I had some rare down time so I did a compression test this evening and here are the results:
1) 121
2) 119
3) 120
4) 119
5) 120
6) 120
The only thing noteworthy was the #6 plug was very black in comparison to the others. When I have another free evening I do plan to throw on a vacuum gauage and see how it reads. But so far, do these numbers look healthy enough to start throwing on a few upgrades (offy intake, 4 barrel and either the HD, efi manifolds or headers). I was already kind of planning on pulling the motor as I have a RMS leak. So just wondering if it would be money well spent or worth doing anything while its out? Thank you in advance for any advise.
1) 121
2) 119
3) 120
4) 119
5) 120
6) 120
The only thing noteworthy was the #6 plug was very black in comparison to the others. When I have another free evening I do plan to throw on a vacuum gauage and see how it reads. But so far, do these numbers look healthy enough to start throwing on a few upgrades (offy intake, 4 barrel and either the HD, efi manifolds or headers). I was already kind of planning on pulling the motor as I have a RMS leak. So just wondering if it would be money well spent or worth doing anything while its out? Thank you in advance for any advise.
Logistics Pro
Joined: Mar 2009
Posts: 4,855
Likes: 609
From: Minnesota
I think you have a very good base to work from. I would pull it to do the RMS as it is much easier out then in. You will also be able to clean it better as well. Think about pulling the freeze plugs and hosing out the block to clean any debris out. This also allows you to replace 40+ year old parts.
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Tuned
Joined: Jun 2017
Posts: 279
Likes: 91
From: Indiana
Choke open, but I did not pin the throttle open. I have always heard it does not make much difference.
Laughing Gas
Joined: Jul 1999
Posts: 1,048
Likes: 22
From: Lacey, WA
A closed throttle will lower over all readings due to vacuum restriction. More important is 2 have all readings within 10%.....which you have.
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Posting Guru
Joined: Mar 2016
Posts: 1,412
Likes: 1
From: Barre Mass
X2 on that. Based on the readings you have your at 12% off original spec. Not bad for the age of the motor. I will bet if you do the compression test at WOT it will be better.
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Fleet Mechanic
Joined: May 2001
Posts: 1,396
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From: Cupertino
12% off? According to my 1967 manual, a 240 is speced at 150-200 psi on the compression test.
Nonetheless, methinks the numbers are fine for a driver. With the throttle blocked they would be even better.
Nonetheless, methinks the numbers are fine for a driver. With the throttle blocked they would be even better.
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