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350 ot 400 engine swap ???

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by Rasberry, Jun 12, 2001.

  1. Rasberry

    Rasberry 1/2 ton status

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    My cousin has a 78 blazer with a 400 in it that he is swapping out for a 455. He will give me the 400. My question is how much trouble would it be to swap it out in my 71 Blazer?

    I have a 350 mounted to a TH350 tranny. Will it bolt strait up, and will the motor mounts bolt up and will there be problems with the exhaust. Is this a simple engine swap or is there more than meets the eye?

    Thanks

    Rasberry 71' K/5 Blazer
    http://www.geocities.com/71blazer
     
  2. HarryL

    HarryL 1/2 ton status

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    Rasp,

    Can you say "simple"? direct swap. No problemo. Sehr einfach. muy facil. tres faciliment. Bez problemi.

    do your self a favour and buy new engine mounts, hoses and belts. Now is a good time to spray down the engine bay and slap in a fresh coat of paint.

    Have fun.

    Harry
     
  3. Rasberry

    Rasberry 1/2 ton status

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  4. Triaged

    Triaged 1/2 ton status

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    It is a direct swap. You need the flywheel off of the 400 along with the harmonic balancer. You also might want to think about using your 350 heads on the 400. This will bump up compression (but still allow 87octaine) for more power. 400 motors in stock form put out much less power than a '71 350 because the 400 is a "smog" motor.

    '71 Blazer CST with alot of rust
     
  5. Rasberry

    Rasberry 1/2 ton status

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    The 350 in my blazer now is from a 76 corrvette. I think the heads are 76cc as is, how much lower should I go.

    Thanks


    Rasberry 71' K/5 Blazer
    http://www.geocities.com/71blazer
     
  6. Ryan_B

    Ryan_B Registered Member

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    If your gonna take Triaged advise on putting your 350 heads onto the 400 ....Be Sure You Have The Steam Holes Drilled In Them!
    That is the single most important thing in the difference between 350 heads and 400 heads. 350 heads have no steam holes. 400 heads have steam holes, and you can drill them in 350 heads to make em work on a 400.

    The combustion chamber size (76cc) on your 350 heads may be the same size on the 400, so it would be pointless to swap heads unless you determine the heads your swapping on are a smaller cc.
    You could put in a thinner head gasket, but it will not make a very big difference, perhaps more trouble than it's worth.
     
  7. Triaged

    Triaged 1/2 ton status

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    I am not sure what size the cylinder heads are from the factory. I have the 71 heads on my 400 block. I could try to check and see if no one else knows. 76cc is about as big as it gets though.

    '71 Blazer CST with alot of rust
     
  8. Sodder

    Sodder Registered Member

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    Pretty straight foward just take your time and do it right the first time. Its a whole lot easier and a whole lot less expensive!!! Good luck on your project.
    Sodder
     
  9. 2quicK5

    2quicK5 Registered Member

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    350 and 400 heads from '71 through '86 have 74 or 76 cc combustion chambers. The 74 cc were used on '71-'72 high performance engines (LT-1). So unless you get 1970 or earlier heads, there will be virtually no difference in combustion chamber size and compression ratio. If your '76 vette heads came from an L82 engine and have 2.02" intake valves and 1.60" exhaust valves, you may want to use them instead. Just make sure you drill the steam holes. If they are the standard L48 heads and have 1.94" intake and 1.50" exhaust valves, then don't bother changing them, you won't notice any difference.

    John

    1972 K5 Blazer: 400 ci, 4 sp, 4" springs, 35" Tires

    2000 Trans Am, A4
    11.97@114 mph
     

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