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Projects Six banger guys- need help identifying a Jimmy

Discussion in 'The Hokey Ass Message Board' started by tetanusshot, Dec 3, 2016.

  1. I just received these images via text. I'm not sure if there are visual differences between the GMC motors like the 235 and 261 Chevys. Can anyone tell me if this is a 270?

    He sent me these numbers from the plate right behind the distributor. 06----D2708 --94255

    I would imagine it is a 270 based on the above numbers. But I sure would settle for 302!

    [​IMG][​IMG]
    [​IMG]


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  2. Tman
    Joined: Mar 2, 2001
    Posts: 34,448

    Tman
    ALLIANCE MEMBER

    270 on the pad behind the dizzy is a 270, good find
     
  3. gas pumper
    Joined: Aug 13, 2007
    Posts: 2,956

    gas pumper
    Member

    And its got headers!! Real good find. If it's got a 6 bolt flywheel flange you got a winner there. If no still not bad. Happy Motoring
     

  4. Gofannon
    Joined: Feb 8, 2007
    Posts: 672

    Gofannon
    Member

    You might want to check the head numbers, information courtesy of Patrick's: http://www.patricksantiquecars.com/index.html

    JIMMY BASICS (Read Photo #1: L to Rt, #2 Top to Bottom)
    1. #2136477:
    [​IMG]
    Open (Hemi) chamber, small ports (7/16'). Served as the only head, apparently, for '228, '236, '248, '256 & '270 from 1939 thru approximately 1954, with the sole exception of some '270's which got the new big port "H" head (below). Compression was established by


    2. #2193417:
    [​IMG]
    The legendary "H" head - open chamber, with large 1 3/4" intake ports, introduced in 1950 and used only through '52 after which (819) was used. Great for performance! Forged, custom piston shown.


    3. #2193983:
    [​IMG]
    '302 head - big ports, "D" chamber, always with a 2-barrel carb, it seems. Installed in larger GVW trucks (never pick-ups) from '52 thru '59. An accompanying governor limited rpm's to 3,200. Also, a great performer, with "D" chamber. Custom piston pictured.


    4. #2194819:
    [​IMG]
    Small ports and small chamber. This head was apparently introduced about 1954 to allow lighter, flat-top (or even dished!) pistons on '248 and '270 engines. '236 and '256 engines were already gone and now '228 and '248 were dropped, leaving the '270 to serve in everything down to 1/2 ton. These (6) engines are the "small-block" Jimmy family; sharing rod and main bearing sizes, connecting rods and head-bolt pattern.

    Theoretically, any of the above heads could be installed on any of the blocks. However, the '477 head would be limited in performance by the small ports, and pistons would require some sort of lump (or, "pop-up) to make adequate compression. The '417 and '983 heads make excellent performance application with their large ports and good chamber design, though they are best installed on their respective blocks: '417 on a '270 and '983 on a '302 due to piston configuration. By noting the photo, it is apparent that the '302 head would interfere with the '270 piston, and the "H" head would make less compression with the '302 piston. The 2194819 head is a poor performance candidate by virtue of its small ports and restricted chamber. (note that parts number reveals introductory sequence ) None of the stock GMC pistons is recommended for a performance engine, due to their excessive weight.
     
  5. jimmy six
    Joined: Mar 21, 2006
    Posts: 9,471

    jimmy six
    ALLIANCE MEMBER

    The 819 head is great for street use with a flat top piston with a zero deck height when used with a big port intake. There is enough iron on the head to taper the first 1/2" to port match. This combo gives great velocity when the intake opens and adds to the torque of the engine. I would never waste a 302 on the street when a 270 readily available. They have the same stroke.
    If you look hard enough you can see why the 417 will out perform a 983 and why they are becoming unobtainium ( but not if you are willing to step up) naturally aspirated.
     
  6. 6inarow
    Joined: Jan 24, 2007
    Posts: 2,322

    6inarow
    Member

    Take it. I even grab 228s and 248s. they dont make em anymore.
     
  7. Thanks for the advice. As luck would have it, I have found both a 261 Chevy and the 270 GMC at the same time. One of these will ultimately go in a 53 Chevy suburban backed by an S 10 five-speed. The 261 is mechanic owned and is verified to run like a Swiss watch and the 270 will have to go on the current owner's word that it is a good engine. It might be a tough decision to decide which engine to go with for the suburban.

    If there is a way to have my cake and eat it too I will buy both and probably set the 270 aside. Mainly because speed parts seem to be easier and cheaper to source for the 261. By the way, both engines can be had for under 500 apiece!


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