Compression test results

Big Block A body Tech

  1. GREEN GHOST

    GREEN GHOST Well-Known Member

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    Just finished testing compression this afternoon, results below are cold & dry. From everything I red the numbers seem higher than what I would've expected for a healthy engine. It's a 500ci 440 stroker with approx. 10.5-1 compression and a small hydraulic cam. Are the higher numbers a result of the baby cam ? Or is the CR possibly higher than I'm thinking?. .. . .cylinder 6 will remain a mystery and I'm ok with that lol. Just getting the spark plug out was a hellacious event that took 15min & had me wishing the car had a 408 in it . . .couldn't imagine a hemi in this thing
     
    Last edited: Dec 27, 2021
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    • GREEN GHOST

      GREEN GHOST Well-Known Member

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      20211227_154018.jpg
       
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      • 69conv

        69conv error 401 FABO Gold Member

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        You got the tough ones out. Sometimes its easier with a wrench from underneath 1 sixteenth at a time.
         
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        • GREEN GHOST

          GREEN GHOST Well-Known Member

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          2 & 4 I had to do from under the car , 8 was no prob from up top. . .6 OMG just taking the plug out from under the car was painful.
           
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          • 69conv

            69conv error 401 FABO Gold Member

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            Some people drill a hole from the fender and put a body plug in to make access easier. My 400 Dart is the 1 sixteenth from underneath variety!
             
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            • DrCharles

              DrCharles Well-Known Member

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              My 451 Dart is of this variety :D
               
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              • fishmens67

                fishmens67 FABO Gold Member FABO Gold Member

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                low deck takes me 20 minutes or less to change plugs.
                45 plus years of experience helps. :)
                 
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                • Garrett Ellison

                  Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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                  Give us the cam specs and what the installed centerline is. Also, altitude, crank stroke, and rod length. You may be able to retard the cam four degrees to bleed off some compression if you have detonation problems you find are impossible to tune out. I would recommend a proper solid lifter cam (well really a mechanical roller with matching hardware, if you can afford it) in any stroker build. Really a waste of a good stroker kit if the valve opening rate isn't maximized, unless you built it for a motorhome or a dump truck. A flat tappet hydraulic might be okay if it's big enough, but I wouldn't risk it with the current lifter issues.
                   
                  Last edited: Dec 27, 2021
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                  • DrCharles

                    DrCharles Well-Known Member

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                    I only have 41 years experience wrenching on my vehicles, so #6 plug is a little harder for me. :rolleyes:

                    Also I don't have two elbow joints in each arm which you would need if you had my (Hedman 78030 B-body) headers and no inner fender hole.
                     
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                    • fishmens67

                      fishmens67 FABO Gold Member FABO Gold Member

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                      20 minutes with 78030 B- body headers.
                      I had them on the 67 Fastback and a 68 Dart.
                      Still have my fastback, be right back I'm going to change the plugs. lol :lol:
                       
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                      • GREEN GHOST

                        GREEN GHOST Well-Known Member

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                        Also forgot to add that after the seemingly endless threads of the spark plug the thing dropped on my throat. . Insult to injury I guess
                         
                        Last edited: Dec 27, 2021
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                        • GREEN GHOST

                          GREEN GHOST Well-Known Member

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                          Lol . . .I have the large tti headers & raised port promaxx heads . . .mine might be a worst case scenario
                           
                          Last edited: Dec 27, 2021
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                          • GREEN GHOST

                            GREEN GHOST Well-Known Member

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                            I'm planning on changing the carb, intake, & cam so any advice is much appreciated. I'm still trying to figure out the exact combo but what I know for sure:
                            Rod brand / size ( see copied post)
                            Pistons (see copied post)
                            Cam (see cam card)
                            750 dp holley
                            M1 intake
                            Promaxx Victor raised port style head
                            Tti large headers
                            1.6 roller rockers so cam should act slightly larger on lift
                            I have to confirm the crank, but fairly certain it's an eagle 4.25. Some forum members who are more knowledgeable than myself where nice enough to help me figure out the particulars below
                            SmartSelect_20211227-202735_Samsung Internet.jpg 20211121_193022.jpg
                             
                          • Garrett Ellison

                            Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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                            Much respect for anyone with the fortitude to deal with that kind of fight…
                             
                          • Garrett Ellison

                            Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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                            Okay, to figure out your compression we need the installed intake centerline and the rod and stroke length, without a doubt. If you have the numbers from the pistons, that would help. But right off the top of my head without using a dynamic compression ratio calculator, I’m thinking your compression is closer to 11:1, going by the cranking compression numbers you posted.
                             
                          • GREEN GHOST

                            GREEN GHOST Well-Known Member

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                            11:1 with aluminum heads is still ok with 93 pump correct? . . .why would they put such a small cam in a higher compression engine ?
                             
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                            • TT5.9mag

                              TT5.9mag Two atmospheres are better than one

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                              What’s the problem? Are you getting detonation? Does it not run well? Why are you doing a compression test? Show some pics of the plugs you pulled out.
                               
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                              • Garrett Ellison

                                Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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                                But yes, what issues led you to want to check compression? And well, it's not that it's usually a small cam, but it does have an intake closing of 63 degrees. Assuming you're at average altitude of 250 feet of elevation in NJ, the figures show with a 7.1 inch rod and a 4.25 inch stroke, and an average of 190 PSI cranking PSI, that if the cam is installed "straight up", you have 11.2:1 compression, on the nose. And even if it's worse case scenario of the cam having been installed four degrees advanced (I would certainly hope someone installing a cam in stroker wouldn't advance it, it's not like it's going to need any more bottom end torque with a 230 @ .050 intake duration!) it would still have 10.8:1 compression. But it can be premium pump (preferably 93 or 94 octane) compatible with efficient closed or heart shaped chambers. I've seen 11.2:1 with the same cam and similar (195) cranking pressure in a 391 stroker 318 with Edelbrock heads, and with enough tuning, it ran well on premium pump 93. What intake, cam, and carburetor will be dependent on what it weighs, and what gear, transmission, and converter, if applicable.
                                 
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                                • TT5.9mag

                                  TT5.9mag Two atmospheres are better than one

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                                  I run a 236/242 @050 hyd roller in a 496 BBC. It’s in a jet boat so I needed the power in the 5600 rpm range and it’s just about perfect. I’d say for a street car/burnout machine with 500ish cubes that thing should make lots of usable torque and you won’t have to twist it up all the time to do it. If you can tune it, that’ll be the key with 190 psi cranking.
                                   
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                                  • Garrett Ellison

                                    Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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                                    Oh, no doubt it could the tune could be optimized for street driving. What are the overall goals and plans for the car? You may not need to change anything.
                                     
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                                    • Bewy

                                      Bewy Well-Known Member

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                                      Unfortunately, if you are having a problem, #6 might be the cause.......
                                       
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                                      • RustyRatRod

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

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                                        Simple trick to get hard to get to plugs out and in. Break them loose with "whatever" you can first, then get a length of fuel hose and slide over the end and turn them out. Reinstall them the same way. You can work right around header tubes like that. This is why it pays to put some kind of high temperature lubricant on the threads, so they will be easy to remove.
                                         
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                                        • GREEN GHOST

                                          GREEN GHOST Well-Known Member

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                                          The previous owner told me that some times it will start to run rough due to the valve seals in cylinder 3 needing to be replaced. After letting it sit a couple weeks I took it out yesterday and it was just not running well. Some forum members recommended I do a compression test while the plugs are out before I start on changing the seals. The plugs looked pretty trashed, all are black with varying degrees of wetness
                                          20211227_153945.jpg
                                           
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                                          • GREEN GHOST

                                            GREEN GHOST Well-Known Member

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                                            I remeber reading that trick awhile ago & totally forgot until you mentioned it. 100% the route I'm going to go when reinstalling
                                             
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                                            • GREEN GHOST

                                              GREEN GHOST Well-Known Member

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                                              I'd really like to have at least a mid 11 second ride (would love to break 10s) & be able drive fairly comfortably on the street. No power brakes / steering so vacuum really isn't a concern. I'm fine with pretty much a max cruise of 60 -65mph, also only using spring / summer / fall & nicer weather
                                               
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