350 vs 340 Difference

Discussion in 'Small Block Tech' started by Rustyh1, Oct 17, 2018.

  1. Rustyh1

    Rustyh1 Member

    I inherited a 1967 skylark from my wife’s uncle. I remember him saying that it was a 350 one time, he was a mechanic his whole life so I always assumed that’s what it was. Doing research it appears that’s it’s probably a 340 4 barrel. Is there any way to visually determine what motor it is. It’s a convertible if that matters. Looking to get the car going for my daughter to drive in high school in about 4 years. Car has 80,000 original miles and been garaged since 1981.
  2. flynbuick

    flynbuick Super Moderator Staff Member

    Take a flashlight and look on the step down between the carb and the firewall. Unless it has been changed, you will see 340 cast into the block facing up. If it is a 350 Buick "350" will appear. The Buck 350 was introduced in the 68 model year.
  3. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    The easy way to tell at a glance is to look at the exhaust manifolds, if the exhaust ports are spread out then its a 340, if the 2 center ports are right next to each other then its a 350.
  4. Rustyh1

    Rustyh1 Member

    Thanks, trying to decide what direction to go with this car kinda leaning to a 350 swap. Do you know if the brackets alternator etc will swap from this motor to a 350 Buick?
  5. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Everything should swap no problem, make sure you use the right water pump because IIRC there is like 3 different lengths and if you have the wrong one for the 340 pulleys they won't line up.

    What's wrong with the 340?
  6. Rustyh1

    Rustyh1 Member

    Don’t know. Just trying to figure out if I want to drop in a mild built 350 or get current motor running. With the compression on that motor what would be required to run current gas?
  7. 300sbb_overkill

    300sbb_overkill WWG1WGA. MAGA

    Turn the key and start it.:D

    But seriously depending on the factory compression rating for your engine midgrade or premium should be fine.
  8. patwhac

    patwhac Well-Known Member

    Yeah I would add new oil prime it with a drill and have at it! Then you can compression test it to see what shape it's in. May need to clean fuel tank/new fuel pump/rebuild carb? Was the tank drained before it was stored?

    Check out this thread, it has good tips for starting an engine that has not been run in years:

  9. alec296

    alec296 i need another buick

    340-350 basically same dimensions and external parts. Same crank and rods. Timing cover. Built 350 is pretty much a direct swap. 340-4 would probably only be 9.4 compression. Should be ok on 87-92 octane depending on tune.
    300sbb_overkill likes this.
  10. 12lives

    12lives Engage! - Jean-Luc Picard

    340-4 was high compression. 10.25:1 (IF new...) I run premium in mine and watch for pinging! Very good motor, runs strong, just little aftermarket support. Exhaust manifold on drivers side might crack, gives a little puff when broken. Choke comes from tiny pipe in pass exhaust manifold, usually rusted out but can be repaired. Uses a Carter AFB. You get a switchpitch trans with some interesting switches on the intake manifold and firewall - again very solid, runs forever.
    Last edited: Oct 17, 2018
  11. Rustyh1

    Rustyh1 Member

    thanks everyone for the replies. I think I’m going to try to get it running and maybe slowly piece together a 455. I’m sure I’ll have many more dumb questions as this goes on.

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