Looking for more 408 pull at the big end?

Discussion in 'Small Block Mopar Engine' started by MichaelB., Dec 3, 2018.

  1. MichaelB.

    MichaelB. Well-Known Member

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    So I built a 408 a few years ago. Started out just looking for under 500HP. About half way through the build I got a little amped up and went farther. Ended up with Eddy Magnum heads, polished massaged & deep port matched to an airgap by Hughes, then bolted on 1 7/8 race headers by TTi with 3.5 collector, KB forged pistons (11.0:1) Big Howard's cam (Duration @ .050": 248I/254E, Lift: .578"I/.590"E, Lobe separation 108) MSD and a 850 Dominator. Put a 100 shot plate system too. Might be too much for my Eagle cast crank with Eagle I beams (whoops got them 1st).

    Anyhow went to the strip & ran some mild 1/8 mile all motor passes while breaking it in. Car launches great on 28 inch slicks 4:10 gearset 3500 stall 904. Three passes net nearly identical traps: 60 ft = 1.5, 330 = 4.7, 1/8th = 7.4 @ 91MPH consistently. Ninety one... I was looking for more in the 100MPH range. Don't you agree?

    Car is pulling like a freight train. No skips or hiccups, great smooth power up to 6000 RPM shifts. I just feel like the trap speed is showing a weakness... If I were to tune up something (other than the driver) for more top end charge what would you go for 1st?
     
  2. B3422w5

    B3422w5 Well-Known Member

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    Cam to me seems small. I would want something more approaching 260@50
    Also its gonna be a lot faster with a real convertor.
    To give you an idea, i have stock stroke 360. Howards 260/264 cam. 10.3 compression. 1 5/8 headers. 950, airgap. 410 gear. Runs 94 in 1/8 1.52 60 foot, but 5200 convertor. Right at 3300 with me in it. Mild ported eddies. My cam is a hair too big, but was in stock when i needed one quick. Perfect for yours.
    Two things..... convertor, are the heads good. Heads not good= low power. But convertor definately far from optimal
     
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    • MichaelB.

      MichaelB. Well-Known Member

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      Hmmm. Heads? Heck I figured with Edelbrock and Hughes I was bound to come out alright. I would not have thought that would be the limiting factor. Converter tho'. Yes I know its mild but seems to fit my type of use. I guess that is pretty easy to swap though.

      I thought for sure my 1st ping from the crowd would be the airgap!
       
    • mopardrew

      mopardrew Member

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      Did you say cast eagle crank?
       
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      • MichaelB.

        MichaelB. Well-Known Member

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        Yeah... That was ordered moons ago without enough research. Sorry! Plans were to upgrade to a forged Scat or something... With that said that is the reason why I am asking for other thoughts ~ as now would be the time right?
         
      • B3422w5

        B3422w5 Well-Known Member

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        Airgap isnt going to hurt it at all shifting it at 6
         
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        • moper

          moper FABO Gold Member FABO Gold Member

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          What gear and RPM are you trapping at in the 1/8th?
           
        • MOPAROFFICIAL

          MOPAROFFICIAL Well-Known Member

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          On the ported eddys. ...What final intake port volume did you end up at?

          That would help in your quest for top end by means of bigger cam.
           
        • MichaelB.

          MichaelB. Well-Known Member

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          Alright sir. I like that manifold so that works for me.

          Going strictly by my brain recall - 3rd @ 5300RPM.

          I do not have that port data. We casually had a number but I did not gather a chart. Bigger cam would be a easy upgrade. But keep in mind that I am running a 1.6 ratio (magnum) rocker and my spec is from a 1.5 listing for that cam. I was under the impression that the 1.6 would give me a more aggressive end spec.
           
        • replicaracer43

          replicaracer43 Old school member

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          I'd bet that the head is the cork, not the cam. A edelbrock head really isn't big enough for a stroked small block in a race configuration, IMHO, it's really a street replacement head for 340/360 combos
           
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          • MichaelB.

            MichaelB. Well-Known Member

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            I found an old spec in my stack of papers. "195cc intake runner"
             
          • moper

            moper FABO Gold Member FABO Gold Member

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            Who made the convertor?
             
          • MichaelB.

            MichaelB. Well-Known Member

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            Even the Magnum version? Heck I picked that one myself. I WAS pretty proud of that!

            TCI Super Street Fighter 3500 stall converter
             
          • B3422w5

            B3422w5 Well-Known Member

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            Head( if its any good) is enough to go 130 mph in an A body. Its too small for sure, but it will support 550 horse falling off a log on the right shortblock.
            I am not much( at all) of a Hughes fan. But if the head is any better at all than stock i would guess most of the problem is the convertor. Its definately hurting that combo
            Should run high 90’s in the 1/8, 122 or so in the 1/4
             
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            • crackedback

              crackedback FABO Gold Member FABO Gold Member

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              Either the tune up is WAY off or the heads don't work well.

              Brians Duster went 96 with 408 making about 480hp at 3350# with a 4.56 gear and hughes 3500 shelf converter.

              Timing, jetting, air to carb, something isn't right as the MPH is way down. If your car is lighter than Brians, It's REALLY off tune wise.
               
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              • thesiren74

                thesiren74 Well-Known Member

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                6,000 seems a little low? My brother shifts at 6,300 with his 410 from 6,000 and picked up a bunch.
                 
              • thesiren74

                thesiren74 Well-Known Member

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                Yeah i had that same converter worked ok for a while behind my 360 then started slowing down.
                 
              • MichaelB.

                MichaelB. Well-Known Member

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                I think it should too. I figured I was on the right track. Thank you.

                Its light. I have not spent a lot of time on the tune. I was just getting warmed up and breaking it in taking it easier with 90% hits.

                Yes, that is right. I was planning on a full RPM run after a few more passes and a solid nut & bolt check. I figured 6000 was good for now then sneak it up to maybe 6500.

                All of this is very much appreciated.
                 
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                • thesiren74

                  thesiren74 Well-Known Member

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                  12.10s to 11.80s in the 1/4 when i told him to crank it up!
                   
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                  • MOPAROFFICIAL

                    MOPAROFFICIAL Well-Known Member

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                    Are those the big mouth Hughes heads?
                     
                  • MichaelB.

                    MichaelB. Well-Known Member

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                    Nope. Considered those but simply ordered Eddie Magnum small chambers and told Hughes to clean them up out of the box. They got me an airgap then suggested polish & deep porting to match 'em up. That fit my budget.
                     
                  • replicaracer43

                    replicaracer43 Old school member

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                    I would concentrate on the basics first, tuning ect, then converter, then heads. I don't think the head is big enough for the cubes, but I bet some sharp tuning will make quite a bit of difference
                     
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                    • BlooDSMeaR

                      BlooDSMeaR Member

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                      I have the same issue with my 408, I'm running out of camshaft. The cam I wanted was the Hughes
                      HUG SER5054ALN-10.
                      My engine builder convinced me to go with a much smaller cam and I am at max power @ 5500. I lost 40 HP and 50LB TQ from my first cam. Both builds were done on the dyno.
                      Now you have some background, I am running Eddy heads, stock out of the box. I wanted to do the Hughes CNC port job, but once again my engine builder told me they did it once and the finished numbers were not worth the cost. I have since fired my engine builder and am going to pull the motor at the end of next season an install a set of indy heads.
                       
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                      • RAMM

                        RAMM Well-Known Member

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                        The camshaft isn't the problem. There isn't a non-offset rocker head that will support a 4" stroker to spin much higher than 5500-5800. You can cam it, header it, single plane it, carb it, till the cows come home, won't help. Part of my mild disdain for strokers is exactly this. J.Rob
                         
                      • 70aarcuda

                        70aarcuda Master Hoader of SBM FABO Gold Member

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                        so....our 410 in our 71 Dart has run a best of 10.38 @ 127 here in Vegas air....shifting a 6500 rpm and running it out the back door at 6900 rpm....

                        So you are saying we should shift no higher then 5800 rpm...and it will run faster?

                        in the desert we dont get to see cows....

                        dam....new converter cost me 1300 bucks....and it will flash to 5400....going to be some fast shifting...and probably need change dana 60 to 3.54 gears......the money i could have saved by running this thread.
                         
                        Last edited: Dec 3, 2018
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                        • RAMM

                          RAMM Well-Known Member

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                          First of all you didn't mention your cylinder heads. I bet they aren't unported Edelbrocks.
                          Second of all there are exceptions to every rule. Third if I was racing you and told you to shift @ 5800 to go faster I would win. J.Rob
                           
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