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Thread: Rebuilding a 350

  1. #11
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    I sent you an email on my 1972 block. I have all the parts and extras of anything you would need

    Johb

  2. #12
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    This is a useful read

  3. #13
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    I know I am late to the party but here is some info:

    The 68 and 69 Buick 350s oil the top end of the engine though a passage into the heads... This seems to work fine
    The 70-81 engines oil the top end of the engine through the pushrods which also works well. However you just need to know this in the case of mixing and matching parts from different engines. The pushrods are a different diameter and obviously hollow for the later versions

    The 74-81 heads have different shaped passages, and we prefer the 68-73 heads for performance use. Some of the 75-81 heads have oversized valves in the exhaust side, bt no real performance gain in stock form.

    The 68-71 heads are more likely to crack, MANY cracked early heads out there...

    In mid 72 Buick added an extra passage to the heads and this eliminated the cracking issues. The blocks also received an extra "scallop" which covers the new head passage for a dead end but it is needed to keep the coolant from pouring into the valley area of the engine.... If you use late heads on an early block the coolant will pour into the block and make a mess.

    The later blocks can be used with any year head even early versions.

    If converting the 68-69 engines to pushrod oiling just block the oil passage in the block and use all the newer style parts for the top end...

    One bit of testing that i am working on is flow testing the 68, 69, 70, 71, 72, 73, 74 and 77 heads so that I can see which years flow the best....

    So far the most desirable head seems to be the 73 versions because they have the extra coolant passage but they are not the poorer flowing style from 74 and later...

    So if you are buying a complete engine to do a quick rebuild I think the 68-70 engines are the best...

    If doing a modified rebuild then the best is to use a 74-81 engine with 73 heads... this way you get the stronger rods, pushrod oiling system, larger pickup in the oil pan (I don't remember which year that started).

    Another warning though is if mixing and matching the rods and pistons there are two different weights... The 68-72 engines have the lighter rods and the crank is balanced to match that. If you swap to the stronger 74-81 rods it throws off the balance of the engine... Plus most engines under 500 HP are fine with the "weaker" old style rods.... Its only for the 500+ HP Buick 350s that we really need the later rods anyways...

    Regarding pistons there are several dish and compression heights on the 350 pistons over the years... Ranging from about 10:1 compression down to about 7.8:1. The advertised compression ratios were all HIGHER than the actual compression ratio they had....

    Scotty Brown (Buyracingparts) is making nice light forged pistons for us for about $600 which can be custom ordered to get any compression ratio you want without milling much off the block.

    All the Buick 350 heads are about 58 CC unless they are milled.

    I checked the compression ratio on the 71 Buick 350 in my Skylark and it was about 7.9:1 compression, with a Poston 114 cam, home head porting, custom intake manifold and some boost it still made 450 HP at the tires but it really needed that boost!
    Sean G
    70 Skylark-Twin turbo 350 powered
    75 Regal-350
    76 Century-350
    78 Skyhawk-V6
    and 18 spare Buick 350s in the barn.

  4. #14
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    The advertised compression ratios were all HIGHER than the actual compression ratio they had


    that applies to pretty much any factory engine at least until you have a machinist blue print it.

    as a fer instance, actual deck height of the block is usually a bit taller than theoretical design spec. that's going to drop compression over "factory rating" all by itself.



    Regarding pistons there are several dish and compression heights on the 350 pistons over the years...



    OEM rods are all the same length though?

    if the later rods happen to be slightly longer we could pin early shallow dish pistons on them and get a bit more compression.

    obviously, the rotating assembly should *always* get rebalanced after changing major components.
    The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
    Vladimir Lenin

    Government schooling is about "the perfect organization of the hive."
    H.H. Goddard, Human Efficiency (1920)

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