273 piston options

Small Block Mopar Engine

  1. 360DartGT66

    360DartGT66 Not a 360 anymore FABO Gold Member

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    I'm building a 273. Please don't say I should go with a 360 in stead, I won't.

    I want to be able to rev the engine as high as possible. The stock slugs make this difficult (if I could even find a set of stock 0.030" over stock slugs).

    When it comes to the stock pistons and rods: what is the limit in terms of rpm?

    I've found two viable options for pistons.

    1. Egge 10:1 pistons: Egge Piston Set with Pins – Egge Machine Company
    2. Ford 5.4 pistons, Ford stroker rods and 3.58" (360) stroke crank.

    The Egge pistons are just cast aluminum. What would be the rpm limit on those? They are lighter than stock, but not by a lot, maybe 10%.

    (These particular Ford pistons are hypereutectic but there are forged ones to be had, of course. Not sure if I need that, I won't be boosting it.)

    Does anyone have a better idea?

    Now, there is the third option of custom pistons, did anyone do this? What are we talking in terms of cost? Where to order?

    The Ford combo:
    The pistons are pretty much the same bore. 3.63" vs. stock 3.625. I would probably be needing to go with 0.020" or 0.030" over pistons, the block needs to be bored and squared up.
    The compression height is significantly smaller though. 1.157" vs stock 1.822" Hence the need for a longer rod.
    The rods are 6.657" vs stock 6.123" and differ from stock when it comes to journal size and Big End width. The journal needs to come down from 2.125" to 2.086", a difference of 0.039". Not impossible, right?
    The big ends of the rods need to be ground from 0.94" to 0.927", a total of 0.013" or 0.0065" on each side. My machinist can do this, no problem. Probably not even very expensive.
    A third option would be to offset grind the stock crank by 0.030" and deck the block 0.100" and use the same piston and rods. Decking the block 0.1" will cause all sorts of pain with the intake and general fitment but I don't want to stroke the engine, I would like to keep it as stock as possible. I would actually rather de-stroke it but that would make my compression height problem even worse.

    So, thoughts? Tips? Used 0.030" over 12.5:1 pistons laying around?
     
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    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      I say keep it as Chrysler intended and give Egge the nod. Their pistons are NICE. I have a set in my 331 Hemi.
       
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      • 360DartGT66

        360DartGT66 Not a 360 anymore FABO Gold Member

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        You're up late, Rusty!
        Yeah, Toolmanmike likes the ones he has in his 273 too. It is - by far - the cheaper option and since the going price for a 273 isn't all that high, it's probably the more sensible choice.
         
        Last edited: Jan 15, 2022 at 2:28 AM
      • RustyRatRod

        RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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        I'm not having a good week. Haven't slept well in a long time now. I think I'm fixin to die.
         
      • 360DartGT66

        360DartGT66 Not a 360 anymore FABO Gold Member

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        That would be a shame. Who could possibly take your place here?
         
      • RustyRatRod

        RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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        lol. Now that's a goodun right there.
         
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        • Oldiron440

          Oldiron440 Well-Known Member

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          What is the intended use for this combination and how high do you want to turn it?
          The 12.5 pistons you have and E-85 would work but you'd need to run a Holley or a Holley knock off.
           
          Last edited: Jan 15, 2022 at 6:51 AM
        • Charrlie_S

          Charrlie_S Well-Known Member

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          My opinion. Either the Egge pistons (most economical) or a custom piston for your crank and rods.
          The Ford parts combo you listed seems quite expensive.
           
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          • toolmanmike

            toolmanmike Moderator Staff Member FABO Gold Member

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            Hey @memike, that guy with the race Valiant you post pics of, he is running a 273 isn't he? Wonder what his combo is?
             
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            • Oldmanmopar

              Oldmanmopar Going left turning right FABO Gold Member

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              We bought a set of early commando domed from egge's they also have the later 4bbl flat tops. I have a set here if you want pictures to see what they look like.
               
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              • azaustin

                azaustin FABO Gold Member FABO Gold Member

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                I didn’t know there were two different types of Commando pistons. Is there any advantage to the domed piston?.
                 
              • memike

                memike Super Moderator Staff Member FABO Gold Member

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                Yes, I learned about his build over 8 years ago Mike. I can't recall what magazine or drag racers news paper i seen it in.
                 
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                • JDMopar

                  JDMopar Well-Known Member

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                  My 273 is at the machine shop right now. I bought a nice set of NOS .030 flat top pistons for it, but they ended up being too far in the hole to get proper compression. My buddy that is doing the machine work is a HP engine builder for NASCAR folks and has a lot of connections. He called a company called Race Tech, and they are making me set of custom forged pistons for my motor. The price is barely more than the Egge pistons and we are getting modern ring grooves instead of 60-year-old stuff. Race Tech will build you some pistons to your specs, so if you decide to go that route you will need to have your engine builder/machinist to measure twice and order once...lol.
                   
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                  • azaustin

                    azaustin FABO Gold Member FABO Gold Member

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                    JE used to make custom pistons, don’t know if they still do. A friend of mine used to work there and had them make me a custom big bore piston for my XR400 Honda. It was a very nice piston and has been in the bike since 2004.
                     
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                    • 66fs

                      66fs FABO Gold Member FABO Gold Member

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                      How far on the hole were they?
                       
                    • 66fs

                      66fs FABO Gold Member FABO Gold Member

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                      Flat tops are 2 barrel pistons with 4 valve reliefs.
                       
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                      • 360DartGT66

                        360DartGT66 Not a 360 anymore FABO Gold Member

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                        The ones I’m considering (Egge) are supposedly 10:1. There were forged TRW 12.5:1 pistons made back in the day - allegedly.
                        The intended use is weekend drag race and the occasional parking lot donut.
                         
                      • 360DartGT66

                        360DartGT66 Not a 360 anymore FABO Gold Member

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                        They no longer make any pistons for the 273. Neither does anyone else. Except Egge.
                        AFAIK.
                         
                      • 360DartGT66

                        360DartGT66 Not a 360 anymore FABO Gold Member

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                        Compression only.
                         
                      • 360DartGT66

                        360DartGT66 Not a 360 anymore FABO Gold Member

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                        I’ve seen pics and both Toolmanmike and Rusty attest to the quality of the pistons.
                         
                      • 360DartGT66

                        360DartGT66 Not a 360 anymore FABO Gold Member

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                        This is very interesting.
                        Is there any way we could work together here? Are you getting 0.030” over pistons then? What will be the specs?
                        I’ll gladly cover some of the cost if I can piggyback off the work you’ve put in.
                        Mind if I give you a call later?
                        Send me a PM with your number in that case.
                         
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                        • Rat Bastid

                          Rat Bastid .004 light

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                          The first question is how high do you want to turn the engine? And actual RPM or close approximation would help.

                          The second question is why? Cost is a big factor in RPM. The cost of everything goes up by an order of magnitude once you go past 7k. 7k to 8k or so is an order of magnitude. 8k to 85k is another. And it gets worse from there.

                          It’s not just pistons to worry about. Is block rigidity. Crank rigidity. Rod strength. Valve train. Oiling issues. And on and on. RPM is cool. RPM makes power. RPM costs big $$$$$$$$$$. And requires incredible maintenance.

                          That’s why I asked.
                           
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                          • 360DartGT66

                            360DartGT66 Not a 360 anymore FABO Gold Member

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                            Yes. Not cheap. There are cheaper options for rods though.
                            I’d really rather avoid that option.
                             
                          • 360DartGT66

                            360DartGT66 Not a 360 anymore FABO Gold Member

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                            I’d like to say 7k but as high as the stock stuff that’s going in it will allow - for now.
                            If I buys pistons that fit the stock rods then that’s what’s going in it now.
                            I’ll be using the stock rockers and flat tappet lifters for now.
                            I’ve got a set of solid roller lifters but I’m thinking solid flat tappet for starters. I dount think that will be the limiting factor just yet.
                            I’ll be doing oiling mods and Adding a stiffer spring to the Melling 72HV pump I found in the engine when I took it apart.
                            This is going to be a fun project for me, not a race engine. If the parts I choose limit me to 6k then that’s what the limit will be. Until I decide to buy a better crank and rods. Or springs and rockers if that’s what’s limiting me.
                            Short version: I’m aiming for 7k.
                             
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                            • Plymouth 65

                              Plymouth 65 Floorable Deplorable

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                              Thes 273 Commando pistons were above the deck and have 2 valve reliefes. 65'
                               
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