SBC to BBB Swap

Discussion in 'Street/strip 400/430/455' started by 69SkylarkGS, Aug 8, 2019.

  1. 69SkylarkGS

    69SkylarkGS Well-Known Member

    I have a 1969 GS350 the previous owner put a SBC 350 in. I’m preparing to start the process of swapping in a low mileage 1970 455 out of a big car to restore it to it’s Buick glory. The engine is on it’s way here and should be here next week. It is complete from carb to pan with accessories, including factory air parts. My car was a factory air car too. It still has it’s original Muncie M21, posi rear with 3.42 gears. I’m looking for advice on anything I’ll need to switch over or change in order to complete this swap. I’ve come up with the following through research;
    1- motor mounts/frame pads
    2-bell housing
    3- clutch
    4-relocate fuel lines
    5-exhaust work/downpipe
    The car currently has full length headers with a custom exhaust and flow masters. I figured I can probably reuse the flowmasters and rear section of the exhaust but will need metal work to cut and weld the front section. Any recommendations here?
    6- flywheel
    The engine I’m receiving is out of a big car so was hooked to a th400 and has a flex plate. I’ll probably buy a billet flywheel.
    7- aluminum radiator
    8- 455 fan shroud
    Any recommendations on what shroud to use when putting a 70 455 into s 69 GS?

    Anything I’m missing? Thank you for your help in advance! This is my first Buick at 33 years old so please excuse my ignorance. I am willing to learn though.
     
    Donuts & Peelouts likes this.
  2. Philip66

    Philip66 Well-Known Member

    1. You'll just need 68-72 a-body motor mounts and frame pads. The big car motor mounts are different. You can buy aluminum or steel frame pads from T/A Perf. and the holes are already there in your engine cradle.

    5. I would imagine you could use a good portion of the head pipe too.
    A SBC header exits fairly close to where a BBB header would exit. I would just wire the existing collector pipes off to the side until you have the engine mounted with headers installed, then you can decide where to cut.

    8. Finding a BBB fan shroud for a 69 or 70 used to be a chore, but not anymore.
    Both years are very similar and are reproduced in fiberglass. Not sure exactly how much but I'm remembering @ $160-170.00 from T/A. Year-One also carries these.

    That's about all I can help you with but I'm sure some 4 speed guys will be able to give you all the advice you need.

    Cool project, even better with pictures!

    Good Luck!
     
  3. telriv

    telriv Founders Club Member

    I also believe you'll need an oil pan & matching pick-up.
     
  4. 69SkylarkGS

    69SkylarkGS Well-Known Member

    Is there a preferred year fan shroud to use 69 or 70? I’ll probably also be using the stock exhaust manifolds that are coming with the 70 455. They are in good shape and with all my other expenses headers probably won’t be in the budget right now.
     
  5. 69SkylarkGS

    69SkylarkGS Well-Known Member

    So the pan that’s already on the engine won’t fit? I was planning on dropping it and cleaning it out anyway bc the engine has been sitting for many years but I was hoping to reuse it.
     
  6. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    No need to buy a billet flywheel.

    If the 70 engine has a rear sump pan you'll be fine. I can't remember, but it may have a center sump pan.
     
    69SkylarkGS likes this.
  7. Philip66

    Philip66 Well-Known Member

    Since your car is a 69 you will want a 69 fan shroud. There are some differences in the mounting tabs and the holes are also already there in your core support for a 69 BBB. Here's a link to George N.'s Buick Performance Club webpage about the differences between the 69 and 70 fan shroud. Tons of other articles and topics that will help you along the way...

    http://www.buickperformanceclub.com/BBShrouds.htm

    http://www.buickperformanceclub.com/FanShroudModification.htm


    You might want to read this page, it details the differences when swapping from a SBB to a BBB. I realize your going from SBC to BBB but there's a lot of helpful info.

    http://www.buickperformanceclub.com/conversi.htm

    I guess I assumed you were going with headers, sorry.
    If you have a good custom exhaust shop near you they can make you up a pair of head pipes for manifolds. If you're like most of us who have seen the quality custom shops disappear, you can order just a set of head pipes from T/A. They will fit exactly as they should and they will get you far enough back to hook into your existing mufflers/tailpipes.
     
    Last edited: Aug 12, 2019
    Dano and 69SkylarkGS like this.
  8. 69SkylarkGS

    69SkylarkGS Well-Known Member


    Thank you very much for the explanation! I’ll start checking out some of those links. I’ll probably just order the head pipes from TA unless I can find one locally but I’m not familiar with a quality place.
     
  9. 69SkylarkGS

    69SkylarkGS Well-Known Member

    Ok so I’m needing a rear sump pan, that clears it up for me thank you! Hopefully it has one but if not I’ll be looking for one.
     
  10. 1969RIVI

    1969RIVI Well-Known Member

    If your new engine came out of a Riv it will probably have a rear sump pan already.
     
  11. 69SkylarkGS

    69SkylarkGS Well-Known Member

    It came out of a 70 LeSabre
     
  12. 1969RIVI

    1969RIVI Well-Known Member

  13. sriley531

    sriley531 Excommunicado

    Mark Demko and 69SkylarkGS like this.
  14. 1969RIVI

    1969RIVI Well-Known Member

    Oh yeh right, brain fart lol in that case if the engine comes with a center sump and he needs a rear I have one.
     
    sriley531 likes this.
  15. Dwayne B

    Dwayne B Well-Known Member

    I have been considering building one of my 455,s and replacing the 350 in my 72 Skylark.
    I have been back and forth, the little 350 runs pretty good for just 72 stock motor with A TA 212 cam.
     
  16. m louk

    m louk Well-Known Member

    You will need a pilot bushing for the crank
     
  17. 69SkylarkGS

    69SkylarkGS Well-Known Member

    I forgot about the pilot bushing thank you. Some quick research shows that might be a pretty big hiccup as they seem to be hit or miss with fitting. I’ll probably need to measure it and have the bushing machined. That reminds me I’ll also need a big block z bar I believe.
     
  18. Philip66

    Philip66 Well-Known Member

  19. 87GN_70GS

    87GN_70GS Well-Known Member

    May need to drill and tap the side of the block for the z bar stud. Crank may or may not be finish drilled for the pilot
     
    69SkylarkGS likes this.
  20. 69SkylarkGS

    69SkylarkGS Well-Known Member

    I believe the block is already drilled but I’ll double check tomorrow. The engine came yesterday and I got it on the stand today with some much needed help from a friend of mine.
     

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