Safe to swap pistons?

Engine, Trans & Driveline

  1. Bladeruner69

    Bladeruner69 Member

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    So I built a 500" 400 block based stroker 10 years ago and finally got everything up and running earlier this year. The problem that I am having is the static compression ratio and pinging under heavy throttle.

    I have flat top pistons and 88cc heads which gives me a compression of 10.8. My engine builder told me that I should be fine with thicker head gaskets but nope. I have mix or use an octane as is.

    My question is, with very low milage(less than 100) and hours am I able to swap out for some dished pistons and use the same rings to bring the CR down without machining the block?
     
  2. toolmanmike

    toolmanmike Moderator Staff Member FBBO Gold Member

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    How thick are your head gaskets now? There are a lot of different thicknesses available.
     
  3. Xenon

    Xenon Active Member

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    As much as I strongly recommend against it there are shims available for such ..
    https://www.summitracing.com/parts/fel-8519sp/make/dodge

    As toolmanmike ask,, what is current head gasket thickness?
    standard steel is about .020 compressed..
    Fel-Pro blue is about .040 compressed...

    In answer to your question , yes , you can use the current rings again...
    HOWEVER....
    Strongly recommend doing a quick hone before reinstalling..
     
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    • 1 Wild R/T

      1 Wild R/T Well-Known Member

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      What heads are you running? 88cc sounds like Iron heads & if thats the case you'd be better off swapping to aluminum heads
       
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      • wyrmrider

        wyrmrider Well-Known Member

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        E85
        water/ meth injection

        dist curve?

        going to closed chamber heads there is still the compression
         
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        • old guys rule

          old guys rule Well-Known Member

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          Laugh out gaskets has what you need. The gasket they have can lower your compression Rachel about one full point
           
        • old guys rule

          old guys rule Well-Known Member

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          That's flat-out gaskets
           
        • 66Satellite47

          66Satellite47 FBBO Gold Member FBBO Gold Member

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          I agree with Wild, which heads have you got? my 500" EDE RPM head motor worked fine on pump 93. Timing was a conservative 36*, all in at 1200 RPM, just off idle. Which gaskets are you using? Seems like 10.8 would be tough with iron heads. Even with iron heads & head gasket thickness, the right cam could help.
           
        • 493 Mike

          493 Mike FBBO Gold Member FBBO Gold Member

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          More duration will lower that static CR.
          Mike
           
        • yella71

          yella71 Well-Known Member

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          change your heads. use aluminum you will never get away from pinging with iron unless you use 100 octane gas. I don't care what anyone says....
           
          Last edited: Mar 22, 2020
        • Stanton

          Stanton Well-Known Member

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          Felpro make a .052 thick BB head gasket. If you want thicker you can contact these guys: https://www.scegaskets.com/

          Swapping pistons is obviously a bigger and more expensive job !!
           
        • 33 IMP

          33 IMP FBBO Gold Member FBBO Gold Member

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          If you have open chamber iron heads, you already have no quench, so.... summit has cometic mls gaskets at 60, 75, 90 and 125 thousanths thick. Decide which one you need to get the compression ratio to where you want it, and install. They are NOT cheap, but a hell of a lot less money and work than a new set of pistons.
           
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          • 33 IMP

            33 IMP FBBO Gold Member FBBO Gold Member

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            If you have a 4.375 by 4.15 engine with 88cc heads, a typical.025 deck, flattops with a .041 felpro, that calculates to a 10.8 c.r. A .125 cometic will drop that to 9.16 to one. Other adjustments in between are available. Around $250/pair.
             
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            • wyrmrider

              wyrmrider Well-Known Member

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              there are rebuilder shims
              is there an answer on whuih heads?
               
            • threewood

              threewood FBBO Gold Member FBBO Gold Member

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              What cam is installed?
               
            • 1 Wild R/T

              1 Wild R/T Well-Known Member

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              So far we are only guessing, not enough info... My earlier post about what heads for instance, he could be running open chamber Edelbrocks at 88cc or it could be iron.. Either way it's a poor choice since there's no quench.. What cam? A bigger cam might be the best option... Or not..

              Tell us about your build...
               
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              • beanhead

                beanhead Well-Known Member

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                No offense....but you need a different engine builder! 10.8 static and (maybe)no quench, on that lovely northern CA gas? He shoulda knowed better! But, we don't know which heads you have; are they already aluminum? They make them with 88cc chambers. Don't know your piston height, cam timing, ignition curve and timing, is it properly tuned(not too lean?) Anyway--if a piston swap is what you desire (proper pistons will definitely fix your issue) you shouldn't need any 'machining' with bores that fresh..Rings are the cheap part of the equation..
                 
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                • 66Satellite47

                  66Satellite47 FBBO Gold Member FBBO Gold Member

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                  Wild, I wonder how much difference the quench really makes. I don't know, but on my bracket motors, I used both the 906 & 915 heads, equal porting milled to give almost the same static CR, same cams. Both combos made nearly the same power based on actual ET/MPH. The quench difference didn't seem to matter. Any thoughts?

                  But OP does need to give us more detail.
                   
                • beanhead

                  beanhead Well-Known Member

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                  Another thought, have you done a simple compression test to see what the cranking pressure actually is? What if it's really only building 140/cylinder? Then there's something else causing the issue. I'm not saying you're wrong on the info of your own engine, but these things need to be verified before spending the dough and/or tearing into it.
                   
                • 1 Wild R/T

                  1 Wild R/T Well-Known Member

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                  If your running high enough octane fuel quench won't have a huge effect on total power output...
                  It does on the ability to make more power with lower octane fuel without damaging the engine... And for a street driven car it can give improved throttle response at lower rpm..
                   
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