383 needs more power

Magnum Engine Swaps

  1. 71duster383

    71duster383 Member

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    In October’s I purchased a 1971 Duster with a 383 and 727 auto. In the spring I had the car dyno’d and it made 230hp/286ft lb at the wheels. I feel these numbers are lower than they should be. I have a 750 demon carb, Edelbrock dual plane RPM intake, headers, XE284H Comp Cam. Unsure of what heads are on it. Any ideas on what I can do to spruce it up a bit?
     
  2. Fisher

    Fisher Old Guy with a Cool car.

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    About all you can do is change the cam to something with more lift, thats a pretty small cam anyway. and either port the heads you have or buy a decent set of aftermarket aluminum. Does this motor have headers on it now? What is your main use of this car?

    I took a 383 machined in a 440 crank = 426 now. Makes 525 hp and 552 tq. Nice street manners, drives well no complaints.
     
  3. dano

    dano Evil Handy Man

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    The thing about dyno's is they are a tuning tool. You could drive down the street to a different dyno and gain 50hp, or loose 20.

    Was any tuning done to achieve your output?

    Tell us more about your combo. What is the static timing and total timing at what RPM? What ignition system are you using? Have you looked at the plugs to see if you lean or rich? Was the engine rebuilt?
     
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    • Oldiron440

      Oldiron440 Well-Known Member

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      When on the dyno did they tune the carb and timing?
       
    • 318willrun

      318willrun Utube channel 318willrun

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      First post since 2018? Welcome to the site! I would try tuning what you have. I would start with this list:
      1. make sure throttle is coming open all the way
      2. check initial timing
      3. check total timing
      4. check compression
      5. make sure all cylinders are firing (yes, I've seen a dead plug wire)
       
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      • 71duster383

        71duster383 Member

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        No tuning was done. I was hoping the tech would spend more time tuning on it but he told me he was too busy and unfortunately is the only local guy with a dyno. Next one is three hours away. Initially timing is 15 and up to 35. I have a MSD 6A ignition system with a MSD pro billet distributor. Engine was rebuilt in 2012 with all new bearings, pistons, rings and bored .040 over. Peak HP is 4450rpm and peak tq is at 3950rpm. A/F ratio was pretty good on the dyno. Just want a good hp street car. It currently has 4.10 gearing and I want to put in some better highway gears but don’t want to lose the cruising around town fun part either.
         
      • rumblefish360

        rumblefish360 So close, yet so far away FABO Gold Member

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        Stock heads?
        Small-ish cam?

        I think you could change those two items and pick up some really nice torque and hp numbers.

        Tune tune tune!!!!
         
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        • 71duster383

          71duster383 Member

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          What cam and heads would you suggest?
           
        • rumblefish360

          rumblefish360 So close, yet so far away FABO Gold Member

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          Trick flow heads.

          If the cams duration (which dictates the RPM band it operates in) is fine with you, just look to more lift.
          You didn’t mention your compression ratio.
          That could be an issue as well.
           
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        • diymirage

          diymirage HP@idle > hondaHP@redline

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          318willrun gave you 4 good tips, which are all free and possibly the awnser to your problem an you go straight to the $4000.00 answer?

          do the simple and free stuff first


          stupid question for you, when you pop your hood, is the distributor on the front or on the rear of the engine?
           
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          • RustyRatRod

            RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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            He's talking about this camshaft.

            11-651-47 - XTREME Energy™ Hydraulic Flat Tappet Camshafts with 18736542 Firing Order 4 & 7 swap firing order.

            Hardly low lift for a hydraulic flat camshaft. That's a stout camshaft for a stock stroke 383. Which is what we're talkin about here, not a stroker. Apples to oranges and does the OP no good. Lets keep the discussion down to what he HAS so we can better help him. Ok?

            To the OP, first off, how does the car RUN? I mean omitting anything you have learned dyno wise? Are you happy with it? Will it smoke tires? Does it accelerate briskly? It may well be fine, because it's possible to lose 100 HP through the drive train.

            That said, here's where "I" recommend starting. First, run a compression test and post up the numbers. This will give us a good idea about the static and dynamic compression ratios of the engine. My guess is, it will be 120 or less. We can better advise you with compression test numbers so get crackin and let us know.

            You have lots of options. You can taylor the camshaft timing to better match the initial cylinder pressure readings. If they are low, you can advance the camshaft timing. If that engine has stock compression pistons in it, I would put that cam somewhere around 100-102 ICL. But that's getting ahead of ourselves. Lets get those compression test numbers first and we can go from there, ok?
             
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            • RustyRatRod

              RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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              Exactly.

              But no! Lets throw heads and a stroker crank on! geez.
               
            • dano

              dano Evil Handy Man

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            • RustyRatRod

              RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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              Oh ok, I posted the wrong one then. Still though not a small cam for a street non stroked 383.
               
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              • rumblefish360

                rumblefish360 So close, yet so far away FABO Gold Member

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                That should be a healthy power maker. IDK what others think, low .500’s is low lift IMO.

                Honestly I thought it was the next smaller grind.
                My bad, but still hold my stance.
                First thing is first, tune tune tune.
                Visit the track and get the distributor and carb dialed in and see what you get before and after. You might end up happy.
                 
              • RustyRatRod

                RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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                I agree with low lift, but overall, it's a sizeable camshaft for a stock stroke 383.
                 
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                • 71duster383

                  71duster383 Member

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                  Thank you for the direction! It runs really well and I am happy with it right now. It’ll smoke the tires pretty good and snap you back in your seat. But like I said earlier I am hoping to swap the gearing from the 4.10s to something a little more highway drivable but I am worried I will lose the tire smoking ability. I also feel that the numbers are a bit low even for a completely stock 383. I believe a stock 383 is 335 hp at the crank from factory. With the little bit of work that is done to mine, the 230hp at the wheels equates to about the 280hp mark at the crank. (Using 17% drivetrain loss) so I think the power should be available in my engine. It just needs to be brought out. I will get the compression numbers and let you guys know. Thanks for the help. This is my first muscle car and am loving it. Just have lots to learn.
                   
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                  • rumblefish360

                    rumblefish360 So close, yet so far away FABO Gold Member

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                    Ehhh, that figure (hp), was it for the hot engine package or the standard engine package? I forget.

                    The compression could be low and the reason.
                     
                  • RustyRatRod

                    RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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                    Then to hell with what that dyno says. Dynos are like opinions and we all know what those are like. Another dyno might give you a 100 HP difference. Either way. It depends on the dyno somewhat, but moreover, depends on the skill or lack thereof of the person operating it. So take it with a grain of sand.

                    Also, if it smokes tires now, changing to a numerical lower gear set like a 3.55 (puke) will make it smoke tires more, because the tires will be turning more RPM.

                    Again, don't take stock in those dyno numbers. They are just that. numbers. Not performance. et us those compression numbers and we might can help more.
                     
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                    • diymirage

                      diymirage HP@idle > hondaHP@redline

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                      post a pic of the engine
                      (I still want to know where the distributor sits)
                       
                    • 71duster383

                      71duster383 Member

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                      It sits at the front of the engine. E01A1BB3-0447-40D6-8A3C-3123789BA81D.jpeg
                       
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                      • diymirage

                        diymirage HP@idle > hondaHP@redline

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                        awesome
                        that means you got the big block, but posted your question in the small block magnum section of our forum (I was afraid maybe you did have a magnum, in which case the HP numbers weren't unacceptable)
                        don't freak out if this thread disappears, one of our moderators is bound to move it to our big block section:
                        Big Block A body Tech
                         
                      • 71duster383

                        71duster383 Member

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                        Oh shoot! Sorry about that my bad. Ya it’s defiantly a big block.
                         
                      • R4Sedan

                        R4Sedan Forum H/R Dept. President FABO Gold Member

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                        Finally, someone knows how to talk gears. Numbers go down it's LOW they go Up it's geared HI.
                         
                      • 383Scampman

                        383Scampman Well-Known Member

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                        320hp at the tire is a good combo . As was posted before : tune, tune , tune . I have a 383 Scamp and would be very happy with it .
                         
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