early 273 pistons.

Small Block Mopar Engine

  1. pishta

    pishta I know I'm right....

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    I took the heads off a 64 (11-20-63) dated 273 I had collecting dust and found the pistons are pretty high in the bores for a 2bbl design. Flat tops with 4 reliefs 2bbl style BUT they are only .022 in the hole? I measured them with a feeler gauge under a straight edge, .022! Markings are V273 12 7 on the pad and the pistons have a circular pattern on top. I was actually thinking this was an unmolested survivor but it had a felpro .040 head gasket instead of the thin steely so someone was in there at one time. Also there is NO ridge in the bores and no numbers on the piston tops. bore measured 3.629 ish, (maybe the ridge that was removed), but def not a +.010. They also had early 2465315 closed chamber heads so Im wondering what CR these were at.
    20170904_182818.jpg
    20170904_182948.jpg
     
  2. pishta

    pishta I know I'm right....

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    "..64-67 has a pin height of 1.79", 0.031" in the hole and 68-69 has a pin height of 1.82", 0.001" down the hole.." (Mopar Performance Engines 8th Edition) ? Can anyone confirm that or had a 273 open with an almost zero deck piston?
     
  3. clifftt

    clifftt Well-Known Member

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    I've had a '64 2v and currently have a '66 4v Formula S. Those pistons look like the 10:1 (advertised) 4v pistons. The 2v had somewhat of a dish. My 4v were flat with valve reliefs and slightly under the deck when I pulled it apart.
     
  4. 65dartcharger

    65dartcharger Dart Charger 273 Historian FABO Gold Member

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    Interesting! I have a 273 block casted in February 1964 with power pack. Used the same pistons! The block had a special tag attached to it too!
     
  5. SSVDP

    SSVDP Well-Known Member

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    • pishta

      pishta I know I'm right....

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      yeah, Im sure they are not the OEM 2 brow pop up 4bbls. The 68-69 .001 pistons were never used with the closed chamber heads so Im wondering if these pistons are stock or aftermarket. and what the CR was with this combo. Im not really after compression as this will be a turbo motor and I already have the turbo camshaft. Maybe flip 'em for some open chamber heads...

      Ouch, I should have snapped those up. Never saw them.
       
    • nm9stheham

      nm9stheham Well-Known Member

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      Hey Pishta, I just ran some numbers on this, and with .040" thick head gaskets, 62 cc chambers, and estimating about 8 cc's volume in the eyebrows plus in the ring around the perimeter, I come up with a static CR of 7.92. Even with .022" thick head gaskets, the SCR is 8.25.

      So this does look to be the (a) lower compression combination. If it is tight, it may be just right for your turbo setup.

      That all falls out of the pin height and the standard rod length, 1/2 of the stroke, and standard deck height. I can look at a stock 2 BBL '68 piston if you like.
       
    • 66fs

      66fs FABO Gold Member FABO Gold Member

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      I've had a number of early 273's and .020 in the hole is about right for 2 barrel pistons. The original gaskets were composite, not steel shim. The steel shim gaskets were aftermarket by Chrysler.
       
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      • toolmanmike

        toolmanmike Moderator Staff Member FABO Gold Member

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        Back in 64 the 8.5:1 ratio was probably about that! The 4 valve relief pistons are in fact 2 barrel pistons. The 4 barrel pistons are domed like these Egge pistons. 09_24_0.jpg
         
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        • pishta

          pishta I know I'm right....

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          Wow, I thought these would be up there. I had some 318's that were open chamber heads and like .140 in the hole. I can imagine what kerosene those could burn.
           
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          • perfacar

            perfacar Well-Known Member

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            on the 2 bbl 273, the deck is to be, -.011 down. 57.3 chamber with . 020 gasket, comes up 9.5 cr. this is info mopar supplied to NHRA tech.
             
          • 65Val

            65Val Average Length Member

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            My '67 273 had steel shim gaskets. It had never been apart before I did it.
             
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            • nm9stheham

              nm9stheham Well-Known Member

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              Sadly, the factory chambers all seem to measure up larger and the CR is lower. I assumed 62 cc chambers and Pishta's deck height measurement in my numbers for this one. I always take the NHRA numbers as being the max CR that you can machine for in certain NHRA classes, not what is out there stock.
               
            • nm9stheham

              nm9stheham Well-Known Member

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              Yeah, those were the loooow CR truuck 318 pistons. The SCR depends a lot on the starting displacement and you don't have nearly as much here as, say, a 340.
               
            • 66fs

              66fs FABO Gold Member FABO Gold Member

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              Those are minimum numbers. Typically .040 mill on the heads to achieve those numbers. Not sure on decks. If they measured flat and equal, I ran them as is. Not a Class racer, so I could choose what to do.
               
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              • perfacar

                perfacar Well-Known Member

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                I know that, was just stating what max CR can be, I'm not stupid!! usually average CR on those was 8.8 . back off.
                 
              • pishta

                pishta I know I'm right....

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                That would be great, measure the height from top of the pin bore to top of crown if you could.
                 
              • 66fs

                66fs FABO Gold Member FABO Gold Member

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                If you are talking to me, That reply was not for you. It was more for those that followed your post. Having cc'd, a number of heads, It was interesting to me that both J heads and 273 closed chambered heads took .040 to get to NHRA minimum cc's.
                 
                Last edited: Sep 9, 2017
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                • nm9stheham

                  nm9stheham Well-Known Member

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                  Hey Pishta. I measured one and got 1.332" from piston top to top of pin bore. (My dial caliper has sharp edges on the ends of the jaws so I can avoid any added length when measuring to the inside of a hole.)

                  That works out to a compression height of 1.823" which is not what I expected as that would put it right at 0 deck height with standard crank, rods, and block dimensions. I had to scrape down a few thousandths of carbon to get to the AL piston and get that reading. I can do more of them if you like.

                  These came out from what we understood to be a virgin 1968 273. The tops look identical to what you show, with 4 small eyebrows and a bevel on the edge.
                   
                • pishta

                  pishta I know I'm right....

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                  cool, stand by: Ill measure mine once I get one out this afternoon and see if its any different. 1.822 is spec per Deck Height and Compression Distance Data. (but all LA's say that...?) Im trying to detemine if the late 273 was taller than the early due to the open heads they used and the increased compression they claim.
                   
                • nm9stheham

                  nm9stheham Well-Known Member

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                  I looked at your link and the 1.822" dimension is for what is called "Maximum Compression Distance". That works out to be deck height above pin center for the standard rod, crank and block dimensions, but I don't think that is meant to be actual piston compression height. The 318's were way short of that and the 340's longer, yet they list that number for all LA's so that is not actual piston CH.
                   
                • 65Val

                  65Val Average Length Member

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                  I have a chart that says the early pistons (64-67) were 1.79pin height and late pistons (68-69) were 1.82....not sure if it's accurate or not.....YMMV......would that .03 in. make up for the larger,open chambered heads that were available 68-69?
                  MoparSmallBlockPiston-RodsChart.jpg
                   
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                  • nm9stheham

                    nm9stheham Well-Known Member

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                    Hmmmm... that is jiving pretty well with what has been found so far. Is that from some performance book? Tnx!
                     
                  • 65Val

                    65Val Average Length Member

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                    Yes, but I can't remember which one! I think it was Larry Shepard's book. I saved it from a Google Books preview, but can't find it now.
                     
                    Last edited: Sep 9, 2017
                  • pishta

                    pishta I know I'm right....

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                    I got that book. I'll check it as I remember it has an extensive spreadsheet of all the LA pistons dims that I'll scan and post. Duh, I forgot I had it (but cant find it!) . But that dimension ensign called out makes sense now, Thanks nm9. The book lists 9:1 for 68 with open chambers and 8.8 with closed chambers with almost the same pin height. Was the closed chamber head just deep?
                     
                    Last edited: Sep 9, 2017
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