Using used std 70 455 pistons in a std bore 74 stage 1 engine

Discussion in 'Street/strip 400/430/455' started by bamboo72, Sep 7, 2022.

  1. bamboo72

    bamboo72 Well-Known Member

    Does anybody have any respectable comments on I'm using standard 1970 standard bore 455 Pistons with a higher compression rate in a 1974 standard bore 455 stage 1 out of a Riviera? I would prefer not to have to bore if this is an acceptable method any positive feedback or constructive criticism is accepted as I am just not 100% sure if it is the correct thing to do as I say I just do not want to bore the engine if I do not have to and if I I'm able to use the 70 Pistons is there anything special my Builder will have to do to rods or anything else. Yes I have the true stage one heads. Thank you in advance for any and all input and advice
     
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  2. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The reason for boring a cylinder oversize is to correct any wear that causes the cylinders to be out of round and not straight. Seems to me, these are questions that you should be asking your machinist. I mean, how are we to know the condition of your block? Rings seal best in a nice straight, round cylinder. Other than those considerations, there is nothing stopping you from swapping standard bore pistons in a standard bore 455. The dish is shallower on a 1970 piston. The 1970 pistons have roughly 23-25 cc dishes, the 74 pistons are roughly 37-40cc, not sure exactly, but you could measure. There might also be a difference in the compression heights, so the installed pistons might differ some in how far down they sit at TDC. Again, your machinist should be able to calculate what your static compression bump would be by measuring everything.
     
  3. SpecialWagon65

    SpecialWagon65 Ted Nagel

    I've got a similar situation - I've got a used set of 70 pistons and a 72 block I am planning a guerilla build just for a kick.
    We shall see. Need to measure block and so forth.
     
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  4. rmstg2

    rmstg2 Gold Level Contributor

    Depending on the condition of the bore, I wouldn't do it without at least honing the cylinders so the rings will have a better chance of sealing!

    Bob H.
     
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  5. Mark Demko

    Mark Demko Well-Known Member

    I know it’s tempting from a cost standpoint and “I did it myself” BUT a machinist once told me “why would you put round pistons in an out of round hole”
    That stuck with me.
    You’ll probably end up with an oil burner if you try to cut corners.
     
  6. Gary Bohannon

    Gary Bohannon Well-Known Member

    70 pistons have 2 advantages over the 74 piston.
    1. A shallow dish for more compression.
    2. A taller compression distance to put the piston closer to the deck of the block.
    You should have the rods machined to take stronger ARP bolts. You may need to sort through a dozen rods to find a suitable set of 8 due to factory variances in the notched area.
    Check pistons for cracks and diameter of the skirt. Then check bore diameter for fit after honing.
     
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  7. Jim Weise

    Jim Weise EFI/DIS 482

    Knowing what I do about Buick 455 blocks, having measured the out of round and taper in hundreds of them, I would say that it's not likely that the block will be in spec. The thinwall casting we have tends to move around a bit, pushing the cylinders out of round.

    I won't say it's not possible, but not likely.

    Now, all is not lost...

    If in fact you could hone it back straight, then you could send the pistons out to Line2Line coating in Mi and have them apply their APC coating to them. We do this all the time during freshen up builds, although I have never done it to a factory piston. This allows us to straighten the bore back out and still maintain your piston to wall clearance.

    Here is the company/process information

    https://www.line2linecoatings.com/#

    JW
     
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  8. bamboo72

    bamboo72 Well-Known Member

    Thanks for all the info guys, i was thinking ahead about the pistons, the short block has not been torn down yet so wesr and measurements are unknown at the moment. I knew I would get straight forward and honest answers from everybody so that is greatly appreciated, especially from Larry and Jim I appreciate that for getting back to me everybody has good answers. As I say I was thinking ahead if this could be an option or not.
     
  9. No Lift

    No Lift Platinum Level Contributor

    Sometimes you have to do what you have to do. First thing on the block you plan on using is how big is the ridge at the top. You won't be able to tell until you get it apart. If it is not bad then you have a good chance of sucess. You will need to run a glaze breaker on the cylinders. If a machine shop checks the bores for roundness and wear and they say decent they can put a fresh cross hatch on the cylinders.

    The biggest thing you need to do is check the '70 pistons for cracked ring lands. Use one of the old rings and just insert it in the land backwards so you can spin it around the outside. If cracked it may drag. Sometimes that will spot a tight spot that you can do the screwdriver check. You need to place a medium screwdriver between the lands and very carefully, lightly try to pry them apart at multiple positions around the piston. You don't want to pry so hard as to put divots in the land edges. It usually cracks deep inside the groove where the land meets the piston and if it is cracked you can see and feel it give a little as you pry. Obviously, any noteworthy wear on the skirts could be a problem.

    We used to do this all the time but that was back when you could find fairly low mileage blocks and good pistons. Good luck.
     
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  10. Schurkey

    Schurkey Silver Level contributor

    OEM pistons weren't that great to begin with. They're not worth rehabilitating for re-use; if in fact they're in good enough condition to be rehabbed.

    The OEM pistons were too heavy, (antique Buick full-skirt design) and had not-enough compression height. That can't be "fixed".

    Modern pistons can have proper compression height, less weight, thinner rings/lower friction, and overall better quality. The piston top can be better-matched to the combustion chamber of the cylinder head. I wouldn't waste the time it takes to clean the originals if this is an engine where power production is even moderately important.

    OTOH, if rock-bottom price is the utmost concern, you could do worse than '70 pistons IF (big IF) they're in usable condition as described in previous posts.

    This coming from a guy who re-used seven out of eight pistons on the short-block currently in my '88 K1500. The short-block core came from a '97 K1500; the pistons have a modern thin ring package, modern hypereutectic construction for tight piston-to-wall clearance along with consistent weight-matching, and the block was decked .025 to achieve proper squish/quench and slightly improve compression ratio.
     
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  11. Jim Weise

    Jim Weise EFI/DIS 482

    I am sure price is the issue here.. the first piston that is anywhere near the correct spec, is the TA 1611B, now made by RaceTec/Autotec and is at the $700 mark, plus shipping... Last time I checked anyway.. who knows with prices going up every day, you would want to check the current price before buying. The next step is a custom piston, and you not going to get into one of those for less than $1000 bucks these days, from any of the major vendors. Might be able to get a 4032 Autotec for a touch less, but not much.. any of the 2618 material Buick pistons are going to be over 1K. My shelf stock Diamond stroker combo pistons have went from $749, to $850 to now $935.00 First price increase took 9 years, the second one took less than a year... and who knows what the future holds. With all the major piston companies being gobbled up by the same holding company, price competition has gone right out the window.

    Forget about any low price cast piston, unless your aim is to simply make noise and smoke, because short of decking the snot out of everything, you end up at 8 something to one compression.

    That's why the idea of using good 70 Factory pistons has any merit at all. I shutter to think how many of those I threw away over the years, without even looking at them.

    JW
     
  12. Bens99gtp

    Bens99gtp Well-Known Member

    Not saying I would tell anyone to do it, but I ran stk pistons in s motor b4 that was about to kiss the 10 second window. And the piston isn't what went wrong in the end.

    So. I have done this b4 with no issue. But can't say it would work a second time.
     
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