Piston recommendations?

Engine, Trans & Driveline

  1. Portagee

    Portagee Well-Known Member

    Messages:
    51
    Likes Received:
    9
    Joined:
    Nov 11, 2020
    Location:
    Sonoma County, CA
    Local Time:
    2:26 AM
    I'm building a 440 for my '69 bee, and have just finished assembling the short block. For reference, I'm using a '74 block (std bore) with a standard forged crank, six pack rods, and stock flat top pistons.

    I just measured the deck clearance to be 0.150", and a calculated CR of 7.8:1 (using 0.039 gasket and 906 heads, estimating 86cc chambers).

    I read that this is typical for smog engines with low compression, but definitely not what I'm looking for with this engine. I plan to run comp cams' version of the MP purple cam (K21-672-4), so this compression ratio is not gonna cut it.

    Any recommendations on how to address this? I've considered everything from decking the block, milling the heads, using a shim head gasket, etc...

    I'm thinking that the best path forward would be a piston swap, but I don't know how to select the best aftermarket piston for this application.

    Thoughts?


    Thanks,

    Mike
     
  2. 33 IMP

    33 IMP Well-Known Member

    Messages:
    5,256
    Likes Received:
    7079
    Joined:
    Dec 21, 2017
    Location:
    taxifornia,soon 2b Arizona.
    Local Time:
    2:26 AM
    The best choice is absolutely a piston swap, the other methods are bandaids that bring their own problems.
    At theoretical blueprint deck height, pistons with a 2.083 compression height would be zero deck. I have seen flat tops at 2.06, 2.02, and 1.99. Yours appear to be 1.93. You obviously know how to use a compression calculator. Plug in various deck heights till you get the compression you want. With open chamber heads, you dont have any quench to worry about, so head gasket thickness can be juggled to get where you want too.
    I understand that the sixpack pistons really give about 9.5 to one, but.... measure and calculate yourself.
     
    • Agree Agree x 1
    • ruffcut

      ruffcut FBBO Gold Member FBBO Gold Member

      Messages:
      514
      Likes Received:
      694
      Joined:
      Dec 26, 2016
      Location:
      northwestern pa
      Local Time:
      5:26 AM
      I agree with 33Imp. piston swap is the best way to get there. There are lots of off the shelf pistons out there today and you can also get custom pistons at a reasonable price. Just do the math and choose the compression height for your application. Not really that hard as you already know how to measure things correctly! ruffcut
       
    • 440Coronet500

      440Coronet500 Well-Known Member

      Messages:
      1,204
      Likes Received:
      1604
      Joined:
      Jun 27, 2019
      Location:
      Mi
      Local Time:
      5:26 AM
      I would recommend a piston and rod swap. Those 6 pack rods are heavy! So many pistons available today too. With those open chamber 906 heads your going to want your pistons damn near zero deck. 440'
       
    • BSB67

      BSB67 Well-Known Member

      Messages:
      1,616
      Likes Received:
      1314
      Joined:
      Jan 18, 2018
      Location:
      PA
      Local Time:
      5:26 AM
      Boy, it didnt take long to spend $1,000 of the OPs money.
       
      • Like Like x 1
      • 1 Wild R/T

        1 Wild R/T FBBO Gold Member FBBO Gold Member

        Messages:
        4,061
        Likes Received:
        8062
        Joined:
        Jul 9, 2019
        Location:
        California
        Local Time:
        2:26 AM
        When you gotta send out a search party to find the pistons....

        He was already thinking piston swap & asking about the best aftermarket piston for the application...

        440Coronet500 isn't wrong about the 908 rod being heavy & by the time you buy rod bolts & have the rods resized your probably $350 in, CNC Motorsports has the Eagle rods for $515, you can buy a number of rods cheaper but...

        O/P's post. "I'm thinking that the best path forward would be a piston swap, but I don't know how to select the best aftermarket piston for this application."
         
      • Portagee

        Portagee Well-Known Member

        Messages:
        51
        Likes Received:
        9
        Joined:
        Nov 11, 2020
        Location:
        Sonoma County, CA
        Local Time:
        2:26 AM
        :rofl:

        Thanks for thinking of my wallet!

        And thanks to everyone else - I figured a piston swap was the way to go, just wanted others' opinion. And don't need a whole search party to help lol, but do value the opinion of people here who know more than I.

        I'm perfectly capable of finding an aftermarket piston that will fix the compression ratio (didn't mean to say I didn't know how - just that I'd appreciate feedback). However, if anyone else has swapped in aftermarket pistons to work with a stock 440 crank, six pack rods, and 906 heads, I would appreciate hearing about it!

        Thanks!
         
      • 440Coronet500

        440Coronet500 Well-Known Member

        Messages:
        1,204
        Likes Received:
        1604
        Joined:
        Jun 27, 2019
        Location:
        Mi
        Local Time:
        5:26 AM
        For my 440 build I used 2355 Speed Pro forged pistons, stock forged crankshaft, LY rods, 906 heads, Edelbrock RPM Performer intake, 1407 750cfm Edelbrock carb, and a
        298/303 Duration 0.466/0.488 Lift Summit 6401 cam. 440'
         
        • Like Like x 1
        • Portagee

          Portagee Well-Known Member

          Messages:
          51
          Likes Received:
          9
          Joined:
          Nov 11, 2020
          Location:
          Sonoma County, CA
          Local Time:
          2:26 AM
          That's great information, thanks! So looks like those pistons are for 0.030 overbore, so I'll try to find their equivalent stock bore 4.320 pistons and check the CR for my engine.

          How do you like the performance of your 440 with those components? I'll be running a trick flow single plane intake, and my cam has similar duration, but with 0.509 lift - so I'd expect it will be a bit more radical (which is why I'd like the 10:1 CR).

          On a side note - how does everyone feel about swapping out pistons without rebalancing the rotating assembly? I've just had everything balanced to within 1 gram, and have gone from externally balanced to internally balanced and will be running an ATI damper. I would really like to not have to re-balance everything, and hoping I can just weigh the new pistons vs. the old ones and pray they're within a few grams of each other....
           
        • 1 Wild R/T

          1 Wild R/T FBBO Gold Member FBBO Gold Member

          Messages:
          4,061
          Likes Received:
          8062
          Joined:
          Jul 9, 2019
          Location:
          California
          Local Time:
          2:26 AM
          First I don't know how a 400 slipped into this conversation...

          Second if you don't want to re-balnce stick with the 2355, they are heavy like the stock piston.... And BTW 2355 comes in different sizes, naturally the std bore is more $$$$

          https://www.summitracing.com/parts/slp-l-2355f/make/dodge

          I'd buy the cheaper .030 over piston & spend the saving on boring the block...
           
        • F4R/T

          F4R/T Well-Known Member

          Messages:
          1,249
          Likes Received:
          1611
          Joined:
          Jun 17, 2020
          Location:
          Illinois
          Local Time:
          4:26 AM
          I’ve got old speed pro in mine.. big heavy but 11.0:1 .. I like squeeze and with my Mr. Six Pack #4 Cam and lifter set up.
           
        • BSB67

          BSB67 Well-Known Member

          Messages:
          1,616
          Likes Received:
          1314
          Joined:
          Jan 18, 2018
          Location:
          PA
          Local Time:
          5:26 AM
          Im not saying anyone was wrong. But you can kinda tell the guy is on a budget because he just wants to "swap" pistons. Not saying that's right or wrong either.
           
        • lewtot184

          lewtot184 Well-Known Member

          Messages:
          4,665
          Likes Received:
          2951
          Joined:
          Aug 21, 2011
          Location:
          indianapolis
          Local Time:
          5:26 AM
          so, what compression ratio are you shooting for? if the block is finished bore/hone now how will that influence piston choices? what does a 75cc edelbrock head do for you? is the cam you've picked a must have or are there other choices?
           
          • Like Like x 1
          • 440Coronet500

            440Coronet500 Well-Known Member

            Messages:
            1,204
            Likes Received:
            1604
            Joined:
            Jun 27, 2019
            Location:
            Mi
            Local Time:
            5:26 AM
            I agree with 1 Wild R/T, 2355 come in multiple sizes and are heavy like the original pistons. The goal of my build was basically to the 440 HP spec. I used a slightly bigger cam than the stock 440 HP. I always have the rotating assembly balanced on my builds. It makes sense when you change rotating/reciprocating mass. I would discuss this with your engine builder/machinist. The ATI damper is a great choice and the only one I recommend besides Fluid dampers. 440'
             
            • Agree Agree x 1
            • BSB67

              BSB67 Well-Known Member

              Messages:
              1,616
              Likes Received:
              1314
              Joined:
              Jan 18, 2018
              Location:
              PA
              Local Time:
              5:26 AM
              Based on the original post, It's a standard bore, and I believe that initially he was not going to finish bore/hone anything.
               
            • 747mopar

              747mopar FBBO Gold Member FBBO Gold Member

              Messages:
              12,865
              Likes Received:
              16598
              Joined:
              Oct 30, 2012
              Location:
              ohio
              Local Time:
              4:26 AM
              For a street motor I like the Keith Black Hypereutectic pistons, not badly priced and fit tighter in the bore. I've used them on 2 motors now including my current stroker which sounds comparable to yours with no complaints. It's 9.8:1 with 452 heads but being a 400 based stroker the math won't be the same.

              Are your 906's ready to go, do they need rebuilt? I ask because that alone could cost almost as much as a set of heads.
               
            • BSB67

              BSB67 Well-Known Member

              Messages:
              1,616
              Likes Received:
              1314
              Joined:
              Jan 18, 2018
              Location:
              PA
              Local Time:
              5:26 AM
              Yes, you can maintain reasonable balance by swapping the 2235 for what you have. Just check weights as you go.

              But the question you should be asking (well, maybe not) is what does everyone think about putting a new piston in a used bore................
               
              • Agree Agree x 1
              • PRHeads

                PRHeads Well-Known Member

                Messages:
                1,087
                Likes Received:
                1373
                Joined:
                Aug 31, 2018
                Location:
                So. Burlington Vt
                Local Time:
                5:26 AM
                One of the more important considerations I would have with regards to running new pistons in a used bore is....... ring travel near tdc.
                If there is really any kind of wear ridge in the used bore, you don’t want the new pistons to have the rings riding over that ridge when coming up to tdc.

                “If” you can find a taller piston that has the top ring land no farther from the pin c/l than the current pistons, and the ridge is minimal, I’d consider using new pistons in the used bore, provided the wall clearance is within a normal range.

                If the rings would have to ride over the ridge...... I’d have the cylinders bored oversize.
                 
                • Agree Agree x 2
                • BSB67

                  BSB67 Well-Known Member

                  Messages:
                  1,616
                  Likes Received:
                  1314
                  Joined:
                  Jan 18, 2018
                  Location:
                  PA
                  Local Time:
                  5:26 AM
                  This.
                   
                • 1 Wild R/T

                  1 Wild R/T FBBO Gold Member FBBO Gold Member

                  Messages:
                  4,061
                  Likes Received:
                  8062
                  Joined:
                  Jul 9, 2019
                  Location:
                  California
                  Local Time:
                  2:26 AM
                  And at that point your looking at custom pistons... Like I said before best cheap route .030 over 2355's & bore the block..
                   
                  • Agree Agree x 3
                  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
                    By continuing to use this site, you are consenting to our use of cookies.