1964 394 Engine Compression PSI??

Old June 5th, 2018, 05:25 AM
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1964 394 Engine Compression PSI??

I have a '64 Olds 394 Starfire engine, 345 hp. What lbs/square inch (PSI) should I see when I do a compression test? Results taken last evening are as follows: cylinder 1-180 psi, 3-185, 5-182, 7-168, 2-180,4-161, 6-189, 8-166. Thanks for you help!!
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Old June 5th, 2018, 09:58 AM
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When I got my 63 six years ago the engine was said to be rebuilt with about 3000 miles on it. I did a dry compression test and got 180 to 182 psi all around which I was very happy with. Your numbers look good to me.
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Old June 5th, 2018, 11:16 AM
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Thanks Don for taking the time to relay that info to me! Much appreciated. I suppose then that my engine is in decent shape. I still need to do a carb rebuild and repair the exhaust leak. Thanks again!
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Old June 6th, 2018, 03:59 AM
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I looked in an old "Motors Manual 1966" that I have. It says the 394 compression is 190 psi. So I'm a little low on seven of the eight cylinders. I did not test with ALL plugs removed. I tested with only one plug removed at a time. I will retest to determine if this will make a difference.
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Old June 6th, 2018, 07:44 AM
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Originally Posted by BillJack View Post
I looked in an old "Motors Manual 1966" that I have. It says the 394 compression is 190 psi. So I'm a little low on seven of the eight cylinders. I did not test with ALL plugs removed. I tested with only one plug removed at a time. I will retest to determine if this will make a difference.


That will make a difference, don't know which way. My test was with all plugs out and carb wide open, but the engine was cold, ideally it should be hot.
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Old June 6th, 2018, 08:36 AM
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You're probably good enough. There might be a range that's acceptable like 170 to 190. This is a dry test ?
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Old June 6th, 2018, 10:00 AM
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Should be an acceptable PSI range and a percentage difference value. If acceptable was say between 160 to 180 you still wouldn't want seven at 178 and one at 161.
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Old June 7th, 2018, 01:50 AM
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The 1964 Oldsmobile Service Manual (number 1) page 5-3 says to open choke & throttle, remove all spark plugs, and be sure battery is charged. The lowest cylinder should not be less than 80% of the highest, and no cylinder should be less than 100 PSI. A bit of oil can be added to the cylinder to check for ring problems.
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Old June 7th, 2018, 03:58 AM
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Originally Posted by Ozzie View Post
The 1964 Oldsmobile Service Manual (number 1) page 5-3 says to open choke & throttle, remove all spark plugs, and be sure battery is charged. The lowest cylinder should not be less than 80% of the highest, and no cylinder should be less than 100 PSI. A bit of oil can be added to the cylinder to check for ring problems.

BillJack, you can't get any better than from Oldsmobile. I was using 10% variance off the top of my head. Recheck compression PSI and let us know.
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