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  • Engine: 259 High Compression

    Just before putting the Daytona away for the winter, I did a partial "tuneup" by replacing the '63 dated Resistolite ignition wires, rotor, cap and plugs. Also decided I should check the compression pressure to verify all is well ( I just acquired the car 12 months ago). Over the 8 cylinders, there are 6 that register 175-182 psi! This is way high for a stock apparent low mileage 259 engine. The engine has the appearance of never being apart, as the exhaust manifolds had no gaskets.
    The engine is very torquey and pulls well in 3rd gear (auto) with a 3.07 ratio. It doesn't burn oil but leaks some. Fuel mileage is good at 21 mpg (imp) over 3000 miles (trip to Springfield) with A/C some of the time.
    The idle has just a bit of roughness, but that would be due to cylinders 3 & 5 giving 135 & 150 psi respectively. These numbers are not bad for a 259, but in relation to the other six, indicate probable valve leakage.
    The heads are the stock 570's with thin gaskets visible. I'm puzzled by the high cold compression readings. The engine has no indication of being carboned up. The flat top pistons seemed to have normal appearance viewed through the spark plug hole. The heads don't appear to have been milled significantly as they seem to be 3 9/16" thick, give or take a few thousandths, as best as that can be checked on the engine. Any thoughts? Did the factory have any pistons that would push the 259 compression to this level?
    When I removed the plugs, they were all whitish to grey, indicating maybe a bit on the lean side. The carb is the stock 2 barrel and has been run on the 87 octane ethanol fuel. No pinging or knocking has been evident.

  • #2
    If the engine was cold, fuel still connected, and the carb was not held 'wide open' the readings will vary as the cylinders load up with fuel each time you crank it.........................................

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    • #3
      Both throttle and choke were wired full open. The tester is a screw in type with O-ring seal. The engine was spun 'till the pressure max'd - about 4-6 revs.

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      • #4
        I'd compare my gage to a few others

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        • #5
          Gauge was verified at 100 psi. The readings are real!

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          • #6
            When you solve the puzzle, be sure to let us know. I've never seen a stock non-R-series V8 crank 182 PSI.

            jack vines
            PackardV8

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            • #7
              Yea, I know Jack. That's what has got me puzzled. Over the winter period I'll acquire or rig up a leakdown tester to examine cyls. 3&5. If they have normal leakdown, then I'm really puzzled. As per Dan Timberlakes suggestion, I'll get another gauge for a check. However, my US made gauge certainly responds correctly with a noticeably strong reaction to the hose on the higher pressure cylinders.

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              • #8
                Originally posted by WCP View Post
                Yea, I know Jack. That's what has got me puzzled. Over the winter period I'll acquire or rig up a leakdown tester to examine cyls. 3&5. If they have normal leakdown, then I'm really puzzled. As per Dan Timberlakes suggestion, I'll get another gauge for a check. However, my US made gauge certainly responds correctly with a noticeably strong reaction to the hose on the higher pressure cylinders.
                That's your problem the USA gauge trying to work in Canada, it just doesn't know any better, no kidding aside it is an interesting thing to find out about , good luck., let us know what if and when you find it , we have a chapter member that the so called high compression on his new build 289 has him up a tree but he states he is reading 235psi and he has 55 heads and thick gasket, but he is another story.
                Candbstudebakers
                Castro Valley,
                California


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                • #9
                  Welll...

                  If the cam has been advanced...the cylinder pressure will go up...!?

                  Mike

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                  • #10
                    Mike, I've wondered about valve timing. Could the pressure be raised that much? This past winter, I pulled the engine for re-sealing and A/C installation. The timing gears were on the mark, but I didn't check or verify valve timing. I am impressed with the way this engine pulls, making it a very easy car to drive.
                    I just remembered, that I did compare the fibre cam gear with a new one, for keyway position and alignment mark. I don't recall verifying the crank gear mark. This US engine was built on Oct. 30/63.

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                    • #11
                      I guess that it is better to have a good pulling engine, with high compression than one with an even average compression that heats and does'nt run well; like the one in my Hawk that I have never been able to figure out. Just be thankful, David

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                      • #12
                        It may have a lot of carbon build up, which will increase compression. Arco gas on the west coast, and Thorntons on east coast are bad for building carbon up in Studes. I had one build up so bad I coulda spooned the carbon out of the head ports and off the bottom of the valves. It only took about 75,000 miles after rebuild to get that bad.

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                        • #13
                          Well, you say it runs strong and no pinging on regular fuel. Maybe, if it ain't broke, don't fix it.

                          jack vines
                          PackardV8

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                          • #14
                            I agree Jack, but I should sort out the 2 weaker cylinders. A spread of almost 50 psi is way too much. I don't really want to start pulling things down, but I may have a valve or two going away. A leakdown test is in order.
                            As to carbon buildup, you wouldn't think that would be problem after 4000 miles of highway driving on secondary roads, particularly when it runs as well as it does.
                            The overall fuel mileage mentioned above is overstated by probably 5%, as I discovered today that the speedo pinion is a 19 tooth one and so the speedo reads high The car apparently was built with 6.50-15 tires.

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                            • #15
                              Have you check the valve adjustment on 5 & 7 ? They might be off a little causing lower compression and a ruff idle.

                              Gordon S

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