Poly Engine what was good/bad about it and why is the LA better?

Small Block Mopar Engine

  1. bcschief

    bcschief Well-Known Member

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    A really good book that includes poly engines is SA Design How to build Chrysler Engines by Frank Adkins ISBN number is 1-884089-54-2 . Not sure if it is still in print new but should be widely available used.
     
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    • 33IMP

      33IMP Well-Known Member

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      Emissions. Quench also has a dead area, increasing hc emissions.
       
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      • Killer6

        Killer6 Well-Known Member

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        If You saw Christine in the theater, the engine displacement callouts were there, 350. I hadn't heard of one before that, I was thinking "what's this 350 bullshit!?", went to the trusty encyclopedias & Damn!! 1st-year-1-year-only-sho-nuff 350ci Dual-Fury option B engine.
         
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        • 65 Cuda 340

          65 Cuda 340 FABO Gold Member FABO Gold Member

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          Yes, Christine's motor was a big block. That's clear from some of the pix.

          Don't know if the movie car was original in any way, but the optional motor for a 58 Fury was a dual quad 350 big block (as you say, first year for the B motor) with 310 hp. Standard motor in 58 Fury was the dual quad 318.

          High performance 58 Dodges and DeSotos had dual quad 361 big blocks. Dodge had 320 hp, DeSoto somehow got 345 out of the same motor.

          In 58, Chryslers still had the early hemi, with 392 cubes in the New Yorker and 300; lesser models had a 354 poly, which was a Chrysler hemi with poly heads. No relationship to the Plymouth 318 poly, and virtually nothing interchanges.

          Can't remember if the 350 inch B disappeared after 58 or after 59, but it was soon gone.

          The 383 appeared in 59. Had 325 hp with a single four barrel or 345 hp with dual quads. Dodges and DeSotos only. Top Plymouth motor in 59 was a 305 hp 361 four barrel. Next option down was the 260 horse four barrel 318.

          The RB first appeared in 59, with 413 cubes for New Yorkers and 300s, 383 for lesser models. And this Chrysler 383 was a raised deck version, basically a 413 with a smaller bore. It was soon dropped and replaced with the B, low deck 383. Can't remember exactly what year, but by 62 for sure the RB 383 was gone.

          Then came ram induction for big blocks, in all sizes. Long ram, short long ram, and ultimately short ram (AKA cross ram).

          And then the 273 was introduced in the 64 model year, basically a small bore 318 poly with wedge heads. For Valiants, Darts and early Barracudas only at first, but soon was the base V8 in B bodies.

          426 hemi the same year. 440 in 66. Wedge 318 in 67 (in the US). 340 in 68. 360 in 71 and 400 in 72. Last year for big blocks - 1978.
           
          Last edited: Nov 17, 2021
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          • Killer6

            Killer6 Well-Known Member

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            Funny because all the more advanced v8's that replaced the LA-based Magnums have nearly the identical twisted-wedge poly-esque chamber & valve arrangement.
             
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            • tonysrt

              tonysrt FABO Gold Member FABO Gold Member

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              The poly motors had to have rocker arm adjustments and the LA had hydraulics that didn't need adjustment. To me that was an advantage for my Dad. I know Plymouth Polys,277,301 and the 318 had adjustable rocker arms, don't know if they ever became hydraulic or when.
               
            • tonysrt

              tonysrt FABO Gold Member FABO Gold Member

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              The 67 318 had hydraulics. I know because I had to replace 1 on my Dad's car.
               
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              • MOPAROFFICIAL

                MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                LA- Light Assembly.

                The polys weight and its width killed the versatility and the heads lacked high power potential. They didn't peak as high as the later LA's do, they were wider, they weighed more and cost more to to produce. There were a couple cool versions and if you get one of the earlier Poly ' the 325 or 315 or somesheet'...maybe it was the Windsor poly/hemi ..anyhow someodd cid..you could swap that early particular truck hemi head onto the odd ball early poly.
                It may be the truck, 315 or whatever poly that is the one that accepts the pre passenger car 'not the 392/354/331/241 stuff ' but the truck indust type hemi heads.
                 
                Last edited: Nov 17, 2021
              • 65 Cuda 340

                65 Cuda 340 FABO Gold Member FABO Gold Member

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                270, 315 and 325 Dodge poly motors, plus 301, 331 and 354 Chrysler poly motors can all be converted to hemis, using Dodge hemi heads on the Dodge motors, and Chrysler hemi heads on the Chrysler motors.

                57 DeSoto Firesweeps were basically Dodges with DeSoto trim, and used 325 Dodge poly motors. These can be converted to hemis with Dodge hemi heads. There was never an actual DeSoto poly.

                Plymouth used Dodge poly motors in 55 and in lower line 56 models without power pack, in 241, 260 and 270 inch versions. These can be converted to hemis with Dodge hemi heads. The actual Plymouth poly (277, 301, 303, 313, 318 and 326) is its own motor, not based on any hemi motor, and cannot be converted to hemi.
                 
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                • Brooks James

                  Brooks James VET, CPT, Huey Medevac Pilot FABO Gold Member

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                  Damn, i watched that movie closely looking for details. Where were the 350 callouts located ??
                   
                • tonysrt

                  tonysrt FABO Gold Member FABO Gold Member

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                  I don't think they ever mentioned the size of the motor because I had a 58 Fury that only came in Beige and had the 350 motor in it. I think I would have remembered if they called it out.
                   
                • RustyRatRod

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

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                  That's just beautiful. Nowadays, they have to cover engines up with stupid plastic covers because they're ugly and have no personality.
                   
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                  • RustyRatRod

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

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                    It's not hard to see how much straighter a path the airflow has verses the LA heads.
                     
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                    • Brooks James

                      Brooks James VET, CPT, Huey Medevac Pilot FABO Gold Member

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                      Im watching it right now.
                       
                    • Killer6

                      Killer6 Well-Known Member

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                      IIRC Valve cover, My crappy TV/DVD combo gets too blurry when I attempt to freeze/zoom it, but it's there.
                       
                    • harrisonm

                      harrisonm Well-Known Member

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                      You guys all missed the most obvious thing that was GOOD about the 318 Poly....... It was a MOPAR!!!!!
                       
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                      • rumblefish360

                        rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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                        The Poly head design is a good one. The breathing is very good. But the Poly ports are restrictive and the head is not going far in porting. A fella on FBBO did a hell of a job on his. Not for normal car guys for it was a bit unconventional.

                        The newer head? 4.7? That I believe is also a like the Poly head.

                        Im not sure why the Poly didn’t catch on. There are no performance head parts for them. Only recently headers.
                         
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                        • matthon

                          matthon Well-Known Member

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                          I have a poly 2 barrel with headers.
                          Great on gas.
                          Best part, spark plugs are easily accessible, but it runs so well I can't see myself pulling plugs.
                           
                        • Brooks James

                          Brooks James VET, CPT, Huey Medevac Pilot FABO Gold Member

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                          Yes!!! I just finished watching it, I cant believe I miissed. the callouts after watching 4 times !! What a great movie.
                           
                        • Bewy

                          Bewy Well-Known Member

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                          The 318 Poly; brilliant design.
                          One of the few engines out of Detroit where the port sizing, cam specs etc came together to make a spectacular performer. Driving one, it felt more like 418 cubes instead of 318...
                          The poly was handicapped with a low 9:1 CR, but still showed tail lights to many a Chebby or Ferd.
                          Many Dodges & Plymouths were sold here with Polys. All were 2 bbl. Aussie car magazine writers were none to kind to 'Yank Tanks'. But the poly.... They raved about them. I still have magazine road tests where terms like 'Road Rocket', 'Blistering Performance' were used to describe them. A 58 Belvedere was timed at 118 mph, Poly with a 2bbl. They couldn't believe it...
                          I remember a mate of mine had a 59 Belv poly with a lot of miles on it, kept oiling up a plug, so only running on 7 1/2 cyl. He had a mate with a Falcon with a 302 taken out to 312 cubes. The Falcon would have been 300-500 lbs lighter. They had a drag race & at 80 mph, the Falcon driver looked out his window...& saw a red front fender next to his door. Nuff said!
                           
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                          • S'cuder

                            S'cuder FABO Gold Member FABO Gold Member

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                            I'm pretty sure in the book, Christine's engine was a dual quad 318 Poly.
                             
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                            • cudamark

                              cudamark FABO Gold Member FABO Gold Member

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                              The cranks are not the "same". You can interchange them with some caveats. The convertor register is a different diameter, so, you can put the 318 crank into the 273 if you use a reducer bushing for automatic applications, and you can put a 273 crank in a poly 318 application if you machine the crank register to accept the 727 converter button. Manual trans isn't an issue unless you're going from auto to manual on the swap. Then you need to check to see if the pilot hole got the final machining for the bushing, or, you'll need to use the magnum bearing or make a custom bushing as the case may be. Also, the crank swaps should require a rebalance due to the difference in piston weights. This also only applies to the '62-7 polys, as the '61 and older had an extended 8 bolt crank flange.
                               
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                              • dartfever

                                dartfever Well-Known Member

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                                The Poly has a great intake port. The exhaust port really need help though. And as previously mentioned, they can't be hogged out for huge numbers. Here's a pic of mine. 294 HP and 320 TQ. More show than go, but I'm ok with that.
                                satellite first run4.jpg poly dyno.jpg
                                 
                                Last edited: Nov 19, 2021
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                                • toolmanmike

                                  toolmanmike Moderator Staff Member FABO Gold Member

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                                  Nice! And some nice numbers.
                                   
                                • dukeboy_318

                                  dukeboy_318 FABO Gold Member FABO Gold Member

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                                  Weight. Size and cost
                                   
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