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350 or 400?

Discussion in 'The Garage' started by TexasBlazerBoy, Mar 7, 2007.

  1. TexasBlazerBoy

    TexasBlazerBoy 1/2 ton status

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    According to my VIN and LMC's breakdown I have a 400.

    First three letters of my VIN are:

    C=Chevy
    K=4 wheel drive
    R=1977 Model 400-4 V8

    Is there a way to tell the difference between a 350 and a 400?

    I don't think the motor has been replaced.
     
  2. dremu

    dremu Officious Thread Derailer Premium Member

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    Well, casting numbers are always good... but 400's are externally balanced, or something goofy, so the harmonic balancer is different. I'd go look but I sold '77 with the one 400 I had.

    Search on this, especially for any posts by "4x4High", you'll find lots of good info.


    -- A
     
  3. TexasBlazerBoy

    TexasBlazerBoy 1/2 ton status

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    Thanks, this is blowing my mind.
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Suffix code is a pretty cool way to tell too...if its there, HP, carburetion, year, and vehicle will all be specified.

    It's located on the pad just in front of the passenger side cylinder head. Lean over the fender, look straight down in that location, and you'll see the pad. Might need cleaned off to read it.

    Casting number should be at the very back of the engine, looking down.
     
  5. TexasBlazerBoy

    TexasBlazerBoy 1/2 ton status

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    Thank you for the very specific details towards the location I need all the help I can get.:bow:
     
  6. dremu

    dremu Officious Thread Derailer Premium Member

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    Oh, sorry.

    http://www.mortec.com/location.htm

    Everything you ever wanted to know about casting numbers, where to find, what they mean, etc. You coulda searched on "casting numbers" to get that =))

    -- A
     
  7. BadBob

    BadBob 1/2 ton status

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    An even sneakier way for you guys:

    400s have an extra freeze plug in the side of the engine block. So, they should have 3 per side instead of 2. There are some fairly rare 400 blocks that only have 2 and what looks like an undrilled boss for the third. This indicates something, but I forget what (4 bolt main or sommat).
     
  8. dremu

    dremu Officious Thread Derailer Premium Member

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    Weird. 400's are siamesed, right, and only have the cooling passages between alternating cylinders, instead of between each one, right? Seems odd that they'd have more freeze plugs with less passageways.

    ::shrug::

    -- A
     
  9. koldsimer

    koldsimer 1/2 ton status GMOTM Winner

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    Pop your flexplate cover off and take a look at the flexplate. If there is a big metal weight welded to the perimeter of your flexplate, you've got a 400. For about a year, i thought my 400 was a 350. I ended up cracking the flexplate while wheeling one day and when I replaced it, I threw in one for a 350. It vibrated like hell and I had no idea what I could have done wrong. After talking to several transmission guys, one of them told me to check my old flexplate to see if I had a 400. Bingo, 400 sbc!
     
  10. b454rat

    b454rat 1/2 ton status Premium Member

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    Look at the balancer, that is the quickest and easiest way to tell. Looks like grooves in it, and about 8" diameter.
     
  11. BadBob

    BadBob 1/2 ton status

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    You got me man, I didn't cast 'em. :p: Every single one I've ever run across was like that though.
     
  12. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    400 chevy SB is external balanced and has a large weight welded to the engine side of the flexplate. The harmonic balancer is also made in such a way that the outer ring is not perfectly round and smooth all the way around like any other balancer. SOME 400's have 3 freeze plugs on the side, SOME have a casting where a 3rd freeze plug was going to be machined for but most had only 2 freeze plugs per side like any other SBC. An old myth had it that all the 400's with 3 freeze plugs per side were 4 bolt blocks but that is only a myth. I've seen many 400's with 2 bolts that had 3 freeze plugs per side and even more that have the standard 2 per side.
     
  13. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    My 406 is a two freeze plug block.
     

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