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Projects Old school cool 248 Gmc

Discussion in 'The Hokey Ass Message Board' started by Neb Hillbilly, Dec 26, 2019.

  1. RichFox
    Joined: Dec 3, 2006
    Posts: 9,946

    RichFox
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    Size and location of the stock water line upload_2020-6-3_12-33-25.jpeg
     
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  2. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
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    gmcwater.jpeg I was planning to convert the exhaust heated intake to water heated. Is there a reason this won't work? Professional draftsman image included
     
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  3. RichFox
    Joined: Dec 3, 2006
    Posts: 9,946

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    I know lots of people do it. I always thought that when you want the carb heat, your water is cold and how will that help. Later when the engine is warmed up why would I want carb heat? Goes against my pilot training. My Cummins/Dodge had a little hot screen in the intake for starting, Worked great. You could really see it on the volt meter when it was working
     
  4. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
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    Because even after it warms up, it can have icing of the intake. If we only drove our cars when it was 80 deg we wouldn't ever get too. My machinist built a hot 250 and in the summer it ran fine but in the 50-60 degree spring and fall it would hardly run. Of course it is 97 here today so we get all the weather.
     
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  5. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
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  6. Six Ball
    Joined: Oct 8, 2007
    Posts: 3,386

    Six Ball
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    from Nevada

    I have never seen one of those water lines before. Were they only on the military engines?
    Won't the water pressure at the front and back of the head be the same? Why would water flow through the pipe if the pressure is the same on both ends? Does it come directly from the water pump on the passenger side? Should it flow from the rear of the head and return to the neck above the thermostat? Maybe I'm not seeing it right.
    I run exhaust heat from the headers on my 270.
     
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  7. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
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    The there should be higher pressure losses flowing through block because of restrictions. This would allow the tube to be the path of least resistance.

    Sent from my S48c using The H.A.M.B. mobile app
     
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  8. RichFox
    Joined: Dec 3, 2006
    Posts: 9,946

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    That pipe is a good thing. Especially on race/turbocharged motors. It flows to above the thermostat where there is a lower pressure because the thermostat is a restriction. It keeps steam pockets from forming in #5 and 6 near the exhaust valve I highly recommend them. I think during the life of a GMC many were removed during a valve job or rebuild and never reinstalled because the builder didn't know what it was,
     
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  9. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,671

    jimmy six
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    Listen to Rich... for a race or street GMC it is a must. Here it is on my sons 302+ The front thermostat housing is a Chevrolet and the port was for a temp sender. Both have 90* fittings and the tube is 1/2” aluminum. 8177EA45-84CE-4B57-8B56-C0A31E45B362.jpeg
     
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  10. Six Ball
    Joined: Oct 8, 2007
    Posts: 3,386

    Six Ball
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    from Nevada

    I understand what Rich is saying that it returns above the thermostat. That creates a difference in pressure and flow.
     
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  11. RichFox
    Joined: Dec 3, 2006
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    RichFox
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    I may misremember about where it is supposed to go. Looking at JD and my pictures. But it will flow water. Maybe because water at the back of the engine has become hotter and has a slightly higher pressure. I don't know. Still a good thing.
     
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  12. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
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    I plan to run mine in the driverside below the thermostat to make the tubing cleaner. One of my thermostat housings doesn't have that side drilled, the other does.
     
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  13. Six Ball
    Joined: Oct 8, 2007
    Posts: 3,386

    Six Ball
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    from Nevada

    We'll all know soon enough. It may not need a lot of flow. Thermo-syphoning alone should remove the cooler water and it will at the least flow when the thermostat in open. I'm mostly thinking of how a heater flows.
     
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  14. Six Ball
    Joined: Oct 8, 2007
    Posts: 3,386

    Six Ball
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    from Nevada

    This looks like the same engine Rich posted the picture of. It certainly appears to return below the thermostat. I'll shut up now. :oops:

    s-l1600-1.jpg s-l1600-2.jpg
     
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  15. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,671

    jimmy six
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    All of the thermostat housings I have or have seen have all there threaded bosses under the thermostat. We don’t need to worry if it works or not. GMC 6 engineers did that in the 30-40’s for us. I ran my first 10 years without that line because I didn’t know it existed and used the rear fitting for the temp sender. My engine always indicated it was hot. After installation of the line and moving the temperature sender my engines ran consistent and never ever over heated again.
     
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  16. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
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  17. Six Ball
    Joined: Oct 8, 2007
    Posts: 3,386

    Six Ball
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    from Nevada

    After a closer look. :confused: It looks like the tube also connects to the heater out let on the water pump and another tube runs to the right rear of the engine, probably to the heater. That would pressurize both lines directly from the pump. I'd like to actually see one of these neither of my 302s have them and none of my 270s either. All but one had been removed before I got them.
     
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  18. Cosmo49
    Joined: Jan 15, 2007
    Posts: 1,155

    Cosmo49
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    upload_2020-6-5_19-2-13.jpeg
    upload_2020-6-5_19-3-21.jpeg
    upload_2020-6-5_19-3-49.jpeg

    This is a rare piece above the thermostat water inlet neck that came from a (purportedly) 261. The plumbing is to the passenger side DUAL output water pump, water flow to the block BEFORE the thermostat opens.

    Edit #3: I really wish this piece could talk. The original color is a deep Army green.
     

    Attached Files:

    Last edited: Jun 5, 2020
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  19. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,671

    jimmy six
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    A new one for me... thanks for posting a photo...all mine are below the thermostat.
     
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  20. RichFox
    Joined: Dec 3, 2006
    Posts: 9,946

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    My water outlet was a custom made billet piece made by United Air Lines. They just didn't know it. Never payed any attention to a stock one before this thread.
     
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  21. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
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    Getting a few things gone. Degreed and painted the balancer. Drilled and tapped the intake for water. I am using the thermostat housing with both sides drilled. They came on 2 different GMCs I had IMG_20200605_161902.jpeg IMG_20200607_180509.jpeg IMG_20200607_180740.jpeg IMG_20200608_070104.jpeg IMG_20200608_070109.jpeg IMG_20200608_070111.jpeg IMG_20200608_070126.jpeg

    Sent from my S48c using The H.A.M.B. mobile app
     
  22. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
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    Messed with my Mallory s bit before stabbing it in the GMC. Interesting difference between a resistor plug on the left and nonresistor on the right. Both jump the gap but the nonresistor is bright blue. Going to start with R45S plugs but may move to nonresistor NGK if I have problemd IMG_20200610_171001.jpeg

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  23. Please forgive me if I missed it, but what are you going to put this GMC into?


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  24. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
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  25. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
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    Slowly assembling and mocking up parts. Put on the carbs for fun. Exhaust pipe is touching pain rail, not sure what I will do there yet. IMG_20200612_072452.jpeg IMG_20200612_072800.jpeg IMG_20200612_072524.jpeg IMG_20200612_072241.jpeg

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  26. Good progress, great info as always.
     
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  27. jimmy six
    Joined: Mar 21, 2006
    Posts: 6,671

    jimmy six
    Member

    One photo looks like the flange. The other looks line the pipe. I’d put a dent in the pipe or cut a piece out reverse it and weld it back since it’s on the backside.
    Sounds worse than it is but I moved a header like that one time by sticking a 3’ smaller pipe up inside the head an pulling on it away from the block. I’ve moved some 1/2”. Brace the engine before you try this as you could easily tip on over on a stand. Every thing looks great.
     
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  28. Neb Hillbilly
    Joined: Dec 20, 2019
    Posts: 337

    Neb Hillbilly
    Member

    It is touching on the pipe extension. I could grind off the small casting extension but I am temped to bend the header a bit. Which pipe do you guys think should go to the pass side? I am thinking the front pipe under the pan and back. Going to have buy a universal pipe set and decide on mufflers. I am likely going the longest 2.25 center punched glasspacks with a H pipe. I have a GM Finned coil that won't fit the std mount so I am building a plate for off the side cover. I also ordered a ultrasonic cleaner for the BXOV-2s. Hope I can get them cleaned up and looking nice and running even better. Pretty nervous about if they will work but only thing a guy can do is try. Then I need to start building plug wires.
     
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  29. tubman
    Joined: May 16, 2007
    Posts: 5,095

    tubman
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    This is coming together nicely!:)
     
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  30. Six Ball
    Joined: Oct 8, 2007
    Posts: 3,386

    Six Ball
    Member
    from Nevada

    Beautiful!
    I always felt the dual exhaust thing on an inline was a V-8 wanna' be idea. My '53 pickup has duals but they are both on the driver side, side by side all the way back with mufflers staggered. The 153 L4 in my roadster will have one pipe even though the header was designed for duals. The problem with my system is that it adds to the cramped area of the left rear of the engine mount, clutch & brake linkage, master cylinder and lines, + exhaust.
     
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