Compression ratio?

Engine, Trans & Driveline

  1. sabre67

    sabre67 FBBO Gold Member FBBO Gold Member

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    1966 Chrysler 383 2bbl according to My Mopar.com website states that this engine has a 9.2:1 compression ratio. Can anybody verify this C.R. in a factory manual for me? I dont have any 1966 books. Thanks:thankyou:
     
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    • Kern Dog

      Kern Dog FBBO Gold Member FBBO Gold Member

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      No matter what the factory service manual states, it is bullshit. They seemed to LOVE to overestimate the ratios.
      My 1970 383 was rated at 8.7 to one but when I tore it down and measured everything, it came in at 8.12 to 1. It was an original piston, standard bore, UNrebuilt 383.
       
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      • WM23M9

        WM23M9 FBBO Gold Member FBBO Gold Member

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        8.12:1 be correct..
        (Still a Bulletproof, healthy motor.)
         
        Last edited: Mar 2, 2021
      • Kern Dog

        Kern Dog FBBO Gold Member FBBO Gold Member

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        Healthy does not have an E before the Y.
        Be correct yourself.
         
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        • WM23M9

          WM23M9 FBBO Gold Member FBBO Gold Member

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          C'Mon Maaaan! LoL I'm too old for these damn midget FONES.
          20210214_121930.jpg
           
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          • Kern Dog

            Kern Dog FBBO Gold Member FBBO Gold Member

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            • WM23M9

              WM23M9 FBBO Gold Member FBBO Gold Member

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              "A man's Got to Know his Limitations"
              FB_IMG_1609268627081.jpg

              LoL, oops that pic's from 1971's Dirty Harry..
              Briggs-
               
            • yella71

              yella71 Well-Known Member

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              Is this the pissing contest post?
               
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              • 66Satellite47

                66Satellite47 FBBO Gold Member FBBO Gold Member

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                My 1966 Factory Service Manual states the 383 2BBL has a 9.2 CR.
                However, anyone that has actually taken a virgin engine apart has found the published number is high, compared to the ACTUAL measured values. More than likely the actual is around .5 CR lower than advertised.
                 
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                • Don Frelier

                  Don Frelier FBBO Gold Member FBBO Gold Member

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                  We had a 1966 Chrysler Newport with a 383 2barrell. That thing would surprise you, it was just one of those "good ones".
                   
                • 66Satellite47

                  66Satellite47 FBBO Gold Member FBBO Gold Member

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                  My '70 Barracuda Gran Coup had a 383 2 BBL to start with. Added a DP4B & 3310-1 Holley, cheap headers. Would do pretty well on the street. Never lost to a 351 Mach 1, about even with the Chevies of different models & motors. The 340 Darts & Dusters were a major challenge. Lost to most of them. They didn't kill the tires and would run rpm. My last street race was against a '71 454 Chevelle, many rolling goes, he only went by after I lifted when my needle was well past 100. My 383 2BBL base motor was pretty good. Not so much at the track. So I bought my '65 Coronet drag car. Eventually made that a consistent winner.
                   
                • Don Frelier

                  Don Frelier FBBO Gold Member FBBO Gold Member

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                  My cousin had a 70 Gran Coupe 383 super commando.
                  We redid the heads, new chain and put headers on it otherwise it was stock.
                  With G-60 Bias ply tires if you laid a patch and backed up up on it you could nearly pull the front wheels.
                  One of my favorite cars ever never saw any car stay close on the highway from 50-100 even corvettes.
                   
                • diesel_lv

                  diesel_lv Well-Known Member

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                  I love Mopar more than any other, but I've had damn near every make out there. The 351 Mach 1 was a slug off the line. It had a Cleveland which couldn't get out of it's own way unless 3.73 or steeper gears and high revs. The 2bbl heads came w 2.02 intakes and 4bbl came w 2.19's. They were for top end high rev light cars. Now the Windsor was great on the bottom end and could get a 4,200lb pig moving pretty easy.
                   
                • That_Tall_Dude

                  That_Tall_Dude FBBO Gold Member FBBO Gold Member

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                  my 69 2 barrel, was stated to be 9.2 also

                  but that with shim head gaskets and most folks rebuilding don’t use them

                  most folks use a thicker composite, felpro, that drops the compression ~ 1/2 a pt

                  also it’s assuming zero deck which most blocks aren’t, and varied quite a bit

                  Basically have measure to know

                  the big question; why do you want to know?
                   
                • sabre67

                  sabre67 FBBO Gold Member FBBO Gold Member

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                  Looking at cam choices
                   
                • 33 IMP

                  33 IMP Well-Known Member

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                  Then, if your engine has ever had the heads off, the chances are you really have compression in the low 8's, and i would be conservative with a cam choice. ( it probably really had around 8 1/2-8 3/4, and might have lost another 1/4 to 1/2 point from a head gasket change.)
                   
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                  • Kern Dog

                    Kern Dog FBBO Gold Member FBBO Gold Member

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                    The 8.12 CR that I calculated was with a .020 steel head gasket. With a Fel Pro .039 gasket, it drops to 7.85 to 1. Terrible!
                     
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                    • That_Tall_Dude

                      That_Tall_Dude FBBO Gold Member FBBO Gold Member

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                      was this on yours?
                       
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                      • That_Tall_Dude

                        That_Tall_Dude FBBO Gold Member FBBO Gold Member

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                        Only way to make a good cam choice is to know the compression.

                        These blocks vary a bit, and can have the piston below the deck

                        I think mine are .030 with the original 2 barrel pistons that also had small dish

                        but I read about them being quite a way down

                        it really affects 383s CR due to the big bore and short stroke

                        Really kinda need to measure & calculate the CR
                         
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                        • Kern Dog

                          Kern Dog FBBO Gold Member FBBO Gold Member

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                          It was the 383 I rebuilt for this car:
                          2 XH AA.jpg

                          I had first planned to hone the cylinders and rebuild the 383 with the stock pistons. They sat .076 in the hole though. THis put me about a point under the goal.
                          I ended up going .030 over and using Speed Pro pistons that sat .025 below deck, then decked the block to get them at .014. I was aiming to be in the 9.25 CR. The heads I have were milled before I got them and when I checked the volume, they came in at either 83 or 84 ccs. My final CR was something like 9.2 or close to that....right where I was hoping to be.
                          I'm fuzzy on the details but I wrote about it in my build thread titled....
                          https://www.forbbodiesonly.com/moparforum/threads/lookie-what-5000-buys-you.178346/page-37
                           
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