‘68 vs ‘73 350 Crankshaft differences?

Discussion in 'Small Block Tech' started by 68 Lark, Jul 8, 2021.

  1. 68 Lark

    68 Lark All Original 68 Skylark

    Rebuilding my current ‘68 350 SBB with reliability and a step up in performance in mind. Current crankshaft is worn out(already ground down and just lost a rod bearing). I have a ‘73 to use for parts. Any differences in cranks?

    Thanks
     
  2. sean Buick 76

    sean Buick 76 Buick Nut

    Hi, the only difference is the weight of the counterbalance. Any machine shop can re balance it for you though.
     
  3. 68 Lark

    68 Lark All Original 68 Skylark

  4. 68 Lark

    68 Lark All Original 68 Skylark

    @sean Buick 76 Are you aware of any differences in the blocks? Would it make more sense to freshen up the ‘73?
     
  5. sean Buick 76

    sean Buick 76 Buick Nut

    Yes there is one advantage to the 73 block, it has a larger oil pickup passage. I’m
    Not convinced that is any real advantage but it’s physically larger. The main thing is your cylinder head pick. The 73 block can use any year head. The 68 block
    Is only for 68-72 heads.

    I would use which ever block is in the best shape.
     
  6. alvareracing

    alvareracing Platinum Level Contributor

    Sean, does the 350 blocks have such difference in thickness like our BB? Or do they sonic pretty close to each other. I’ve never done a SB but I assume they would be no consistency like the BB.
    Fernando
     
    sean Buick 76 likes this.
  7. sean Buick 76

    sean Buick 76 Buick Nut

    i sonic tested 8 blocks to pick the best one and yes there are wildly different thicknesses. In general the 68-70 blocks have thicker walls however they still have core shift issues. The later blocks are still core shift prone. In general it’s a crapshoot, and my philosophy is to just pick a good running engine and bore it 30 thou without checking the sonic test. I don’t see much point in spending a bunch of time and money to see if an engine can go 60 thou overbore vs spending that time on head porting. I spent the time and money checking & blocks to find the best one as I was planning to shoot for 800+ Hp. That engine has since been slated for a 13:1 NA engine that will likely barely break 500 Hp....

    I’ve since built a new turbo 350 engine that was sonic tested, bored 30 over, girdle, billet crank etc.

    So yes core shift is a big issue, but I wouldn’t even sonic test unless using a power adder, revving over 6500, or trying to bore over 30 over.
     
    patwhac and alvareracing like this.
  8. alec296

    alec296 i need another buick

    Some blocks do test fine for .100 overbore with boost. It’s basically what you intend to use it for.
     
  9. sean Buick 76

    sean Buick 76 Buick Nut

    I would be curious to see long term reliability on a .100 overbore 350.
     
  10. gsjohnny1

    gsjohnny1 Well-Known Member

    i like them when they can over 7500....:D
     
    68 Lark, alec296 and Mart like this.
  11. 68 Lark

    68 Lark All Original 68 Skylark


    Thanks, the '68 block is definitely in better shape. Going to give it a bath and double check everything is still flat. It was bored and decked 5 or so years ago, still looks to be in good shape. The '73 has never been apart.

    What is the difference with the heads? I was looking into TA's stage1 heads for it, wondering if there would be an added benefit with the '73 block and those heads vs '68.
     
  12. sean Buick 76

    sean Buick 76 Buick Nut

    No appreciative performance difference in the heads for performance. I plan on flow bench testing all the year heads to have proof, but I haven’t done it yet. I have all the year Heads on the shelf to test.

    the alum heads are great, however I feel that custom forged pistons and forged rods are needed to make the most of them. $ for dollar I see larger HP potential by optimizing the compression ratio, cam pick, and quick clean up porting on the iron heads.
     

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