1. HP2

    HP2 Member

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    Got myself a 71 Duster a couple of years ago, seller had no clue of engine internals or nothing else but I got a good deal and bought it. Haven't had time for it until now.
    340", Eddie heads, Torker intake, expensive red dp carb, newer crap MP distributor, Hooker Comp headers... that's what you can see.

    Fiber glass hood and bumpers, subframe connectors, full interior, drag radials... Will see mostly short trips and some visits to the 1/8-mile. Stalls around 3,000. Would guess 3.91 gearing. Manual valve body.

    Started it and it run. Drove it home, 7 miles. No noises but run like a pig.
    Did a compression test: 150-154 psi except for cyl 1 with zero. Stamped steel rockers. Exhaust pushrod stamped its own hole in a rocker, his brother intake had an s-shape so I pulled the engine and then the head. Looks all good otherwise. No damage on head, cyl walls look good. Pistons all the way up to deck.
    Single springs seems a little strange with that high lift cam. Will check pressure open and closed.
    Got a set of 273" ductile iron rockers from a friend yesterday. Will check lift and duration on cam tonight. Will also pull pan and see if there's something there I don't want to see there.

    Fiber glass hood and bumpers, subframe connectors, full interior, drag radials... Will see mostly short trips and some visits to the 1/8-mile. Stalls around 3,000. Would guess 3.91 gearing. Manual valve body.

    Have no experience of 340's so looking for advice. I guess to much lift and high revs for OEM rockers and 273" rockers will do?
    What duration, lift and LS would work best with the combo above?

    Thanks!
     
    Last edited: Jun 8, 2021
  2. 440 Charger

    440 Charger FBBO Gold Member FBBO Gold Member

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    Cant help you with the ls.
     
  3. oldkimmer

    oldkimmer FBBO Gold Member FBBO Gold Member

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    How do u know how much lift the cam has. Many back I the day used the factory 340 single spring with a dampner. The street Hemi grind Mopar cam for 1. Even the next size up which is referred to as the 284/484 cam. Pull the front cover a bd timing chain. Their may be some clues there. And yes many were run with the stamped rockers. If u go to the 273 rockers u will need new pushrods. Kim
     
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    • HP2

      HP2 Member

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      I measured both lift and duration with a dial indicator directly on the lifter
       
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      • 1 Wild R/T

        1 Wild R/T FBBO Gold Member FBBO Gold Member

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        And? What numbers did you come up with? Stamped rocker with a hole punched through it I've seen many times... The pushrod next door being a pretzel probably was some kind of contact with pushrod number one...

        No signs of piston/valve contact? Might want to check lift on all sixteen lobes just to be safe... Less then .385 lobe lift should be Okay with the Edelbrock springs if you trust Edelbrock... To be safe .350 would be .525 @ the valve assuming true 1.5 ratio.... Which isn't likely...

        Edelbrock claims their springs are good for .575 lift... 273 rockers & proper length pushrods will probably solve it...
         
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        • oldkimmer

          oldkimmer FBBO Gold Member FBBO Gold Member

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          This is like pulling teeth trying to get information. Kim
           
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          • 440 Charger

            440 Charger FBBO Gold Member FBBO Gold Member

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            Flip the numbers probly a .484 lift and 284 duration I run a .509 lift and 292 duration on stock rockers with no problems other than lopy idel at 1100 rpm. But when they wake up its fun you can do a different ratio rocker and push rods and all the fun stuff if you dont the old scoolers that built them. Lobe seperation is also a thing to look at I run 112 degrees. Cam choices are always interesting for sure all depends what you want it to do .
             
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            • 440 Charger

              440 Charger FBBO Gold Member FBBO Gold Member

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              Never assume that would make an ass out of you and me lol.
               
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              • oldkimmer

                oldkimmer FBBO Gold Member FBBO Gold Member

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                That’s what I said. 284 D. 484 L
                 
              • HP2

                HP2 Member

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                I'm so sorry gentlemen, I beg your pardon! My post didn't come up by some reason and I have been busy on not been able to check my laptop...

                Here is what I came up with:
                217° @ .050 and .507" on intake. Way to small.

                A buddy has an old purple shaft, 292° (248° @ .050) and .508 but it might be to much?
                 
              • HP2

                HP2 Member

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                217° @ .050 and .507" on intake.
                I agree on your guess. That or just over rev.

                No signs at all. Pistons look new. I will need another cam.
                 
              • Curiousyellow71

                Curiousyellow71 Well-Known Member

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                If you don't know what the springs are and you want to know what cam you can run.... measure the coil diameter, number of coils and the installed height. Usually you can figure out what they are and then get a cam. Also measure how far your pistons are down the deck if it's apart, cc the heads and use a online calculator like summits to figure your compression. If you know what piston are in it...usually the mfg lists the valve relief volume on there site.
                217@.050 w .507 lift is a bit odd for a hydr cam????.
                 
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                • RemCharger

                  RemCharger Well-Known Member

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                  What duration do you get @ .002 or .006 lift?
                  That might help steer you in the direction of what that cam is.
                  Check for shitty lobes.
                  I would have slipped a couple rockers on there and some pushrods, to see if 8 cyls pulled the "runs like a pig" out of it.
                   
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                  • BSB67

                    BSB67 Well-Known Member

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                    Very odd indeed. I suspect there is something wrong in the measurements.
                     
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                    • HP2

                      HP2 Member

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                      You are perfectly right. I must have been drunk or something. Now I got my good indicator back so did it all over yesterday. Sorry again
                      All @ .050
                      Intake opens 14 deg BTDC
                      Closes 55 deg ABDC
                      249 deg duration
                      Lift .505
                      Take the numbers with a pinch of salt, as you already have figured out I’m not an expert of taking measurements but this time it should be pretty close!
                       
                    • Curiousyellow71

                      Curiousyellow71 Well-Known Member

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                      Sounds like you have a mp 292.
                      .050 figures Mp uses 298×.85=248.2 @.050
                      Personally I would use the 273 adj rockers, buy better pushrods and do a solid cam.
                      I would not do a mp cam. They are expensive and there is better options. The mp cams do use some aggressive profiles with lift suitable for stamped steel rockers. Just depends on your springs and rocker capabilities.
                      We have old forged Federal Mogul trw pistons in our 340. The block has been decked and they pop up past the deck now. It's also in a 71 duster.
                       
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                      • HP2

                        HP2 Member

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                        I think you are correct about cam, .501 is pretty close to my measurements and when I tried to check advertised or full duration I got 295 degrees. Cam and lifters look all good so I decided to stick with the current stick. The only parts I will need is a set of pushrods.
                        One other weird thing I noticed today is that the pistons is higher on one side than the other. They also pop up past the deck, but .010 on the left side and .035 on the right. Hard to explain, I'll try to upload a pic from my phone. Never seen anything like it, must be an error from manufacturer. Don't know what brand but thinking of taking them out and do a simple honing so then I might be able to find some info on the underside. Anyway, if everything looks good with the pistons I will put them back, even if it's not optimal. 150-154 psi is still good. Fel Pro .039 compressed gaskets.
                         
                      • HP2

                        HP2 Member

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                        E86AA0D7-8DDF-46C3-94FE-E2398B820A16.jpeg B5047A9F-5351-4FFB-B9BF-A417024C447A.jpeg
                         
                      • Cliff Ramsdell

                        Cliff Ramsdell Member

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                        Pistons look like the old TRW L2316 forged piston. If I remember correctly they were positive deck height, about .013” and the stock 340 pistons for ‘68 were the same.

                        Different deck height, that’s worth having a closer look at, .035” is way to much and could cause an issue with the edelbrock heads, I don’t believe they are an open chamber head and the piston could contact the quench area with the wrong gaskets.

                        As for the 273” arms. They are pretty good but not bushed and require the correct rocker shafts with the “banana “ cuts in them for proper lube. Also don’t forget to swap out the stock non locking adjusters for a new set.

                        Good luck,
                        Cliff Ramsdell
                         
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                        • HP2

                          HP2 Member

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                          Engine has been run with this combo and no signs of piston/valve contact so all good about that. Now I have found that cam is 4 deg retarded and I want to change that to 0 deg so will have to check clearance again after that. Anyway, how can pistons be "leaned" to the left?

                          Good point about the banana cuts, will look for them! The non locking OEM has already been changed, but thanks!
                           
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