A12 compression height question

A12 Mopar Discussions

  1. TrackPack

    TrackPack Well-Known Member

    Messages:
    135
    Likes Received:
    77
    Joined:
    Jun 6, 2018
    Location:
    Minnesota
    Local Time:
    2:33 PM
    What was the compression height of the pistons used in the A12 cars? Supposedly the same as the 440 4 BBL's.
     
    Last edited: Mar 10, 2020
  2. BSB67

    BSB67 FBBO Gold Member FBBO Gold Member

    Messages:
    1,054
    Likes Received:
    840
    Joined:
    Jan 18, 2018
    Location:
    PA
    Local Time:
    3:33 PM
    Do you want the exact number? Not sure. From memory, it's close to 2.03. Like 2.029, or 2.032 I have the original NHRA approved Speed Pro forged pistons. It measures 2.034 with calipers.

    It is the same piston as the 68 and 69 4 bbl piston.
     
  3. TrackPack

    TrackPack Well-Known Member

    Messages:
    135
    Likes Received:
    77
    Joined:
    Jun 6, 2018
    Location:
    Minnesota
    Local Time:
    2:33 PM
    Thanks. I'm actually looking for a measurement of the production piston to compare with the L2310 piston that you have.
     
  4. BSB67

    BSB67 FBBO Gold Member FBBO Gold Member

    Messages:
    1,054
    Likes Received:
    840
    Joined:
    Jan 18, 2018
    Location:
    PA
    Local Time:
    3:33 PM
    No. 2286P

    I looked at some info regarding the "original piston" compression height. Says 2.031". But I did not measure it myself, that info is from someone else, but a trustworthy source, FWIW.

    DSC09750 (1280x960).jpg
     
    Last edited: Mar 12, 2020
    • Thanks! Thanks! x 1
    • TrackPack

      TrackPack Well-Known Member

      Messages:
      135
      Likes Received:
      77
      Joined:
      Jun 6, 2018
      Location:
      Minnesota
      Local Time:
      2:33 PM
      Oh, my mistake. Sealed Power 2286 that you measured at 2.034 vs the production 2.031. That helps me out. Thank you.
       
    • BSB67

      BSB67 FBBO Gold Member FBBO Gold Member

      Messages:
      1,054
      Likes Received:
      840
      Joined:
      Jan 18, 2018
      Location:
      PA
      Local Time:
      3:33 PM

      Yes. But I used calipers with them still mounted on the rods. So my measurement could be off a little.
       
    • 33 IMP

      33 IMP FBBO Gold Member FBBO Gold Member

      Messages:
      2,701
      Likes Received:
      3318
      Joined:
      Dec 21, 2017
      Location:
      taxifornia,soon 2b Arizona.
      Local Time:
      12:33 PM
      @BSB67, I think your piston is a 2266 trw. Trw claimed that was a 10/1 piston (hahaha) at .092 down in the hole.
      Trw sixpack forged replacement was L2355F, 022 in the hole, with a 2.061 c.h.
      Trw had four different forged pistons for 440s back in the day, 2266, 2295 (dome),2355, and2388. I have weights, volumes and measurements from a 1989 trw catalog if anybody needs them.
      Unfortunately, i don't have info on original 6pack cast pistons for the op.
      Edit: that 2266 is literally the heaviest piston in my trw book, 880 gr. Plus or minus 10gr.,and a 225gr pin.
       
      Last edited: Mar 12, 2020
    • 1 Wild R/T

      1 Wild R/T Well-Known Member

      Messages:
      1,522
      Likes Received:
      2430
      Joined:
      Jul 9, 2019
      Location:
      California
      Local Time:
      12:33 PM
      10-1 with a 68 cc chamber... To bad the average BBM head has a 88-90 cc chamber....

      And yet if you walked into the average machine shop & ask for a 10-1 440 with forged pistons thats the piston you got nine times out of ten...

      True measured C/R around 8-1... Now cam it for your "10-1" C/R & you have the perfect recipe for a dog.... & I'm not talking about the BBQ served outside the base at Subic Bay PI....
       
    • BSB67

      BSB67 FBBO Gold Member FBBO Gold Member

      Messages:
      1,054
      Likes Received:
      840
      Joined:
      Jan 18, 2018
      Location:
      PA
      Local Time:
      3:33 PM

      Suggesting I cannot read a part number and a caliper? Does this help you. I purposefully purchased these pistons in 1990. They have long since been unavailable. They sit 0.048" in the hole. I have the original bill of sale if you'd like to see it.

      IMG_5199.JPG

      IMG_5192.JPG
       
      Last edited: Mar 12, 2020
    • 33 IMP

      33 IMP FBBO Gold Member FBBO Gold Member

      Messages:
      2,701
      Likes Received:
      3318
      Joined:
      Dec 21, 2017
      Location:
      taxifornia,soon 2b Arizona.
      Local Time:
      12:33 PM
      I was just going by what I could see on your post #4 on my phone. And there is no valid 2286 in my1989 trw book. If its later than that, or a sealed power, than I'm mistaken Sorry, I didn't mean to insult you, and I didn't have access to the better pictures you posted later. And I did say "I think".i didn't suggest anything.
       
      • Like Like x 1
      • BSB67

        BSB67 FBBO Gold Member FBBO Gold Member

        Messages:
        1,054
        Likes Received:
        840
        Joined:
        Jan 18, 2018
        Location:
        PA
        Local Time:
        3:33 PM
        All good. Looking back, I came off a little strong. My apologies.

        Sealed Power. 1990 was probably about the last you could get these.
         
        • Thanks! Thanks! x 1
        • BSB67

          BSB67 FBBO Gold Member FBBO Gold Member

          Messages:
          1,054
          Likes Received:
          840
          Joined:
          Jan 18, 2018
          Location:
          PA
          Local Time:
          3:33 PM
          Yep. If you have a set of 2266s, with some planning you can get its 1.99 compression height to work out okay. It is a replacement for the 67 HP motors and will get you in the upper 9s with 915 heads and a 0.022 gasket. But what usually happened was they got matched up with 906 heads done on the cheap, 0.040 head gasket, and a 509 cam. Turd recipe.

          But it's the 1.92 pistons that are impossible to work with in a NA application.

          I never understood why, back in the 80s and 90s, they bundled these crappy pistons into discounted complete rotating assembly's. They were in all of the magazine's. It wouldn't have cost any more to put the 2355 verses a 2388 pistons in the kit.
           
          Last edited: Mar 14, 2020
          • Thanks! Thanks! x 1
          • Agree Agree x 1
          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.