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GMC 270 & 302 sixes, Need information

Discussion in 'The Hokey Ass Message Board' started by 38Chevy454, May 4, 2006.

  1. I bought a 51 GMC COE, see my other post with pics if interested, it supposedly has the 270 six. I do not have much familiarity with these engines, besides to know that the 302 is the more desireable one. Can anyone provide some resources to learn about them and help me decide what to do with it? My engine has a 4-speed compound low trans. Is the bellhousing pattern same as the Chevy 216/235/262 series? Is the bellhousing able to swap a newer style or OD type trans such as a Muncie or T-5? Is the 270 six even worth messing with? The engine currently has an updraft carb and intake.

    I am planning to replace the engine in the COE with a V-8 with more power and size. So my question is really whether this 270 six engine is worth keeping and what potential use for it in a future project. Thanks for any information and help.
  2. Bluto
    Joined: Feb 15, 2005
    Posts: 4,839


    Check the pad next to the dist. that has the engine size stamped on it

    270's are fine In fact even the smallest GMC is better than a Chevy.When I had the 228 in the 39 it would crap on 235 Chevy powered pick ups. I made enough money to build my 302
  3. Here is the post with my COE that has the 270 in it:

    Also, I forgot about the 228 version Bluto mentioned. I assume that all of the GMC sixes are the same basic block and head design? The differences being bore and stroke? Or is there a lot more to it?
  4. Bluto
    Joined: Feb 15, 2005
    Posts: 4,839


    There's a little more to it

    228,248 share stuff as do 270,302 Exterior dims are the same.Heads pistons differ. They are longer than those Chevy cart-ruck motors :D

    This has caused ''Long motor envy'' since 1939!!! :D
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  5. OldSub
    Joined: Aug 27, 2003
    Posts: 1,064

    Member Emeritus

    270's are worthless junk. Dump yours at my house.

    I've been driving a 270 powered '55 1st GMC Suburban almost daily for the last four years. I'm running a stock SM420 granny gear 4-speed and a GM 10-bolt with 3.08 gears.

    I've used it to tow a trailer loaded with a car and generally choose my more modern big-block powered pickup instead for that kind of activity. Aside from trailer towing I find it very drivable and it will easily run 70+ when appropriate.
  6. squirrel
    Joined: Sep 23, 2004
    Posts: 37,026


    I was wondering how long it would take before someone suggested that
  7. Alfster
    Joined: Jan 15, 2002
    Posts: 1,173


    Worthless engine. You can't make them perform or look good. :D :) :D :)

    Attached Files:

  8. Kinky6
    Joined: May 11, 2003
    Posts: 1,756


    Look right behind the distributor for a flat machined pad, scrape all the munge off, and read the number. First three digits are the engine size, if yours is stock it will most likely be a 270.

    It might be a 248 or 256, but not likely. The 302 didn't come out until '52 or '53, so you wouldn't have that unless its a replacement. Best thing about a 302, aside from the displacement, is compared to the other GMC's it has larger ports and valves in the head, = more air/fuel in & out.

    Now if it does say 270, read further, if it is a 270 H, you have a head that will flow almost as much air as the 302 head.

    These are not cheap engines to build, but with a good cam and aluminum pistons, an improved intake and carbs w/ dual exhaust, they can be a very cool hot rod engine with gobs of torque.

    Oh yeah, and really traditional, too! Later, Kinky6 :cool:
  9. Thanks for the help everyone, I will check this weekend and see what the stamped numbers indicate. The tag on the truck said it was a 270 engine, although it could have a replacement engine over the years.
  10. Tubby
    Joined: Aug 25, 2004
    Posts: 269


  11. Buzznut
    Joined: May 9, 2008
    Posts: 2,353


    I know this is a very old thread, but for the sake of the archives: a 270 has the number 232 4003 stamped in the drivers side. I really wish there were more discussions on parts fabrications, crossover and availability...
    Joined: Jul 30, 2006
    Posts: 1,195


    Yeah where does one begin to look for Hop Up goodies if he's got a GMC 270?
  13. Deucedreamer
    Joined: Jan 11, 2010
    Posts: 425

    from BC Canada

    Patrick's. Or search
  14. badsix
    Joined: Sep 26, 2010
    Posts: 108

    from oregon

  15. Royalshifter
    Joined: May 29, 2005
    Posts: 15,258

    from California

  16. wayfarer
    Joined: Oct 17, 2003
    Posts: 1,776


    The information I have says that casting number is a '55-'63 270
  17. Buzznut
    Joined: May 9, 2008
    Posts: 2,353


    That's correct, I'm not sure about other years. I just received the book "How to Hop Up Chevrolet and GMC Engines" in the mail from Amazon... I'll post more info once I find it.
  18. Spity
    Joined: Dec 20, 2008
    Posts: 438


    For what its worth im under the impression that a chevy inline 6 HEI distributer is a direct drop in, for a hotter spark.

    Please correct me if im wrong someone.
  19. Buzznut
    Joined: May 9, 2008
    Posts: 2,353


    In another thread I was told there are minor modifications needed...not sure what they are.

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