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Are 350 & 400 parts interchangable?

Discussion in 'The Garage' started by BurbLover, Feb 4, 2005.

  1. BurbLover

    BurbLover 1/2 ton status

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    I just got a 79 K10 that the factory sticker by the radiator says its a 400. The guy I bought it from has no idea if it's still the 400 or if it's a 350. Since I don't have time to find the ## on the engine, I need to know if the cap/rotor/plugs/plug wires will be the same for either engine? It need a tuneup so that I can get it to pass emissions and I'm gonna go get the parts tonight.

    TIA!!
     
  2. sweetk30

    sweetk30 professional hooker Premium Member

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    all parts the same for the most part except the crank rods and flexplate/flywheel and balencer.
     
  3. BurbLover

    BurbLover 1/2 ton status

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    Thanks man!! Now I can go to the parts store.

    BTW, I see you're from Horseheads. I'm originally from near Cortland. Actually lived in Virgil, about 1.1 miles from Greek Peak Ski Resort. My dad still lives there. My mom now lives in Marathon. Small world.
     
  4. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    The flexplate and balancer are the only rwo things not interchangeable. A 400 crank obviously will interchange with a 350 (383ci) and the rods will to but I don't know why anyone would want to use 400 rods in anything else.
     
  5. HarryH3

    HarryH3 1 ton status Author

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    A 400 crank isn't a direct drop-in to a 350 block. The main journals on the 400 crank have to be machined down something like 200 thousandths so that it will fit into the 350 block. 350 and 400 rods are different lengths, so you get into oddball pistons to interchange the rods. :cool1:
     
  6. sweetk30

    sweetk30 professional hooker Premium Member

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    exactly!!!! whats up with people latly? most of them cant read the stuff thats been posted already. or mabey i just get the threads that have those people in them:crazy:
     
  7. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    of those things listed, the plugs MAY be a different heat range, but will still interchange.
     
  8. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    I never said a direct drop in... and neither did the original poster. He used "interchange."
    It depends on how technical you want to go with "interchangeability." The balancer and flexplate WILL NOT work at all with a 350 since it is internally balanced. Yes, the 400 crank has slightly larger journals but is an EASY and popular modification for 350's, infact it is no extra work for the engine owner since he has to have an used crank machined anyway. 400 rods will also work with the right piston, but like I said, I don't know why someone would want to use 5.565" rods in anything but a 400 block.
     
  9. BurbLover

    BurbLover 1/2 ton status

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    Okay, my situation is that I need to do a tuneup ASAP on a 79 K10 that I just got. I want to replace plugs, cap/rotor, & plug wires to start with. The original vehicle sticker show the engine in a 400. It appears to have th eoriginal 203 t-case in it. I was just trying to see if I bought the parts for the 400 and it turned out to be a 350 if it would cause a problem.

    I guess I'll know tomorrow after I change out the parts :grin:
     
  10. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    1) I would probably ask for 400 parts since that is what the sticker says, regardless they will fit with either engine.

    2) If you want to tell between a 400 and 350 real fast, look at the harmonic balancer. If the front edge has NO indentations or a "piece" missing and is a complete circle, it should be a 350. If there is a small piece or indentation missing on the edge of the balancer than it should be a 400. ;)
     
  11. BurbLover

    BurbLover 1/2 ton status

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    I'll check that tomorrow when I do the tune up. Thanks.
     

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