Flow numbers and max HP potential

Small Block Mopar Engine

  1. Hot Metal

    Hot Metal '69 440 Cuda

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    my approx 10:1 446ci, 324/290@.050 cam, 906's@265cfm = 524fwhp weight/mph =1.96 hp/cfm. I agree calcs are just a tool but Wallace seems to have been quite accurate for me in the past and our new combo this year according to our weight mph/ET/tyre size/gearing and trap rpm.
     
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    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

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      Another thing on ported heads! There is a lot of voodoo to them when your new. IMO, from what I have done, you would have to go pretty far on a ported head for it not to improve your engine but that can be an easy fence to jump. There is a mixed bag of stuff that needs to be looked at and what your doing as well. A great example of an excellent street head is the TF heads. Small ports, good velocity, this is a good power maker. If you did the same thing with another head but your port window (cross sectional area) is like a race ported big block head designed for a 528 CID engine, well, I think you get the picture on how it is is a big column of air that just won’t move the air due to a small engine of 330/360/408 inches.

      There are various books on this and a few good head porters that can help explain this and perform the work.

      I am not one of them.
       
    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

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      Absolutely, these programs CAN be very good and super helpful.
       
    • 273

      273 Well-Known Member

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      And 2 hp per cfm is also just the rounding of that for a V8.
       
    • 66fs

      66fs FABO Gold Member FABO Gold Member

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      From my experience Heads determine HP, cu in determine where in the rpm range that peak will occur. The theory is spelled out better with real numbers in the following thread. See post #47

      302 heads
       
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      • pittsburghracer

        pittsburghracer FABO Gold Member FABO Gold Member

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        I think I sat next to you at the Bar one night. I was drunk, you was drunkerer. Lol.
         
      • PRH

        PRH Well-Known Member

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        The formula is theoretically stating the “max” hp from the available flow.

        300 x 2 = 600hp

        300 x.26 =78
        78 x 8 = 624hp

        I don’t consider 600 and 624 as the “same”.
        624 is 4% better than 600.

        And, as I have stated....... I have beat both of those formulas numerous times.

        Even recently, by quite a bit.
         
        Last edited: Dec 7, 2020
      • PRH

        PRH Well-Known Member

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        Here’s an excersize for the calculator guys......

        Car race weight = 2750lbs
        Performance = 8.33@165
        Not done in any extraordinarily great air.

        How much power does the motor make?

        How much do the heads flow?
         
      • Hot Metal

        Hot Metal '69 440 Cuda

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        Well I'll bite as the TV is crap and this is better>
        on 165mph=1007hp
        on ET which would normally be 161mph=940hp
        around 490cfm
        and I bet I'm miles out, tell us what your slide rule says.
        I gotta say that when it comes to a stocker forget the wallace calc.
         
      • PRH

        PRH Well-Known Member

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        The Moroso chart shows 950hp for the 165mph, and 940hp for the 8.33.
        (The Moroso chart shows 8.33 should be 164mph, or 165mph should be 8.28)

        These HP numbers aren’t too far off from what it actually made.

        We’ll see if anyone else chimes in.....
         
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        • Hot Metal

          Hot Metal '69 440 Cuda

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          well there's gotta be more than 10hp difference for 4mph faster at that level I would've thought...perhaps the rule has its moments as well and 165 is normally an 8.14.....was it a stick car?...we got a CE car here with a Lenco, runs 7.39@185 which is 4>5mph up@2550lb. Anyhow the slide always was different slighty to wallace.
           
          Last edited: Dec 7, 2020
        • PRH

          PRH Well-Known Member

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          The Moroso chart only shows a 1MPH difference between actual(165) and theoretical(164) based on the 8.33 ET.

          The car ran 1MPH faster than what is theoretically necessary to run an 8.33ET.

          DFCDF5BA-25A6-4082-B9CC-D5E279187160.png

          (So, between your calculator and mine...... we have two different projections of ET vs speed. They can’t both be right.
          The car actually ran 8.33@165...... so doing that is absolutely possible).
           
          Last edited: Dec 7, 2020
        • Hot Metal

          Hot Metal '69 440 Cuda

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          It wouldn't surprise me if wallace was out more, as I understood it the software was designed/based a long time ago on low 12 sec pontiacs etc., its useless for working out on Stock class cars where the mph is down for the ET normally but it still shows normal mph...as in a 9.74 shows 138 with a 1.35 60.....we got a stocker runs that ET@133 +change with 1.28 60's with the rear tyres.
           
          Last edited: Dec 7, 2020
        • Bobzilla

          Bobzilla Well-Known Member

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          Excellent teaser question PRH. Not much going on right now, so I will wager a guess.
          No idea what horsepower would be, and don't know how much it makes a difference for ET compared to horsepower when a chassis really works well, but I am going to guess head flow was in the 375-385 cfm range. Probably way off, but I would follow up by asking if the calculators get farther away from reality in a well sorted car when the volumetric efficiency goes past 100%, and what engine platform was this with?
           
        • pittsburghracer

          pittsburghracer FABO Gold Member FABO Gold Member

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          Weather conditions and track elevation needed. Power adder or NA
           
        • PRH

          PRH Well-Known Member

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          Let’s keep in mind this thread is about potential HP vs head flow.

          I’m trying to take the dyno out of the equation.

          Two calculators are showing 940+hp to get a 2750lb car to go 8.33@165mph.

          So, if the motor has to make at least 940hp to get the car to run those numbers....... how much do the heads have to flow to make that much power?

          Off the top of my head, I can think of 3 different builds where the flow x .26 x 8 formula was off by 100+hp.

          And...... those were combos that had room for improvement...... without improving the flow from the heads.

          Maybe...... pick your favorite hp vs cfm formula and let’s see what it takes.

          One of the Wallace calculators seems to work out to 2.055hp/cfm for an 8 cylinder “typical race” motor.
          As such...... it’s saying 457cfm@28” to make 940hp.

          The flow x .26 x 8 works out to: flow x 2.08...... for a V8, so the Wallace calculator is showing slightly less hp/cfm than this formula.
           
          Last edited: Dec 7, 2020
        • 512Stroker

          512Stroker We are all here because we are not all there.

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          Link to the video?
          I would like to view it.
           
        • Cuda416

          Cuda416 FABO Gold Member FABO Gold Member

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          ]
           
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          • Hot Metal

            Hot Metal '69 440 Cuda

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            ok so you take a TF240 head that flows 326int@600 and 253ex which is 77% of actual flow and use his maths...
            326x.26=84.76x8=678.08hpx77% max flow=522.06 realistic crank hp potential...errr I don't think so, whats this guy on? or have I missed something.
             
          • 66fs

            66fs FABO Gold Member FABO Gold Member

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            As I remember, the .26 number is based on assumptions. "... your running a dual plain intake, and 8.8-10.5:1 compression, want to run pump gas, have a nice wide torque curve, don't want to spin the motor past 7000, and aren't running a stroker." The post I submitted spelled it out, more a rule of thumb. Bench Race away. Thanks, CPDave
             
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            • Cuda416

              Cuda416 FABO Gold Member FABO Gold Member

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              These combos are all naturally aspirated, right? Not that I am questioning anything, just tossing tinder on the fire and watching/learning. This has been a extremely interesting discussion for me.
               
            • flyfish

              flyfish C8H18+N2O = :-D

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              With the 0.26 thing, I don't know where they came up with that, and what all went into the calculation (factors, assumptions, etc) to boil it down to 0.26....but, it happens to be fairly close for my car. My heads flow 293 @ 0.600 on the intake, I have a cam that takes advantage of that lift (about .630 lift)...by my best guestimate from the drag strip, my car makes close to 600hp, depending on parasitic loss and such.

              I think the calculators are nice to give you a ball park estimate, but a savvy engine builder could probably push those limits past the theoretical.
               
            • rumblefish360

              rumblefish360 So close, yet so far away FABO Gold Member

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              I also think it is not a problem. Going past the theoretical isn’t a normal street engine type of build. Also probably not what you would want to do on a NA engine. This is more likely race territory for most. It may very well be, not a very friendly driver at this point.
               
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              • PRH

                PRH Well-Known Member

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                Yes.....N/A.

                The cfm x .26 x 8 can be shortened to cfm x 2.08.
                Supposedly this is for some pump gas, dual plane, street combo?
                Okay...... but the Wallace calculator works out to cfm x 2.055 for what they describe as a “typical race” motor.

                I can tell you this.... cfm x 2.055(or 2.08) doesn’t even get you close to the max hp potential for a well thought out bracket race build.

                Back in the 40’s and 50’s it was thought that it was impossible to go faster than 150mph in the 1/4 mile.
                And there were formulas developed to “prove” it.

                And then the Bustle Bomb went faster than 150....... and that was the end of the validity of that formula.

                One key element to beat the formulas is that the combo has to be “well balanced”. By that I mean, the size of the heads vs the flow, vs the displacement, vs the CR, vs the cam, vs the induction, vs the headers.
                Everything on the same page, working together.
                 
                Last edited: Dec 8, 2020
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                • PRH

                  PRH Well-Known Member

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                  The motor in the car that ran 8.33@165 made 918hp on the engine dyno....... with heads that flowed 390.

                  918/390 = 2.353hp/ci

                  This motor would have picked up 30-50hp just by installing a tunnel ram intake and 2 x 1050 carbs.
                  It could have been built with a little more compression, which would have facilitated a little more duration.
                  The valve lift was kept in check so the springs would have a reasonable life.
                  The vacuum pump used sucked, and would only pull about 4”.
                  If the motor would have been run with 10-12”, more power would have been made.
                  The motor had a very generic, fairly shallow dragster type of oil pan.
                  Something deeper, along with a crank scraper would have freed up a few ponies.
                  Those are all things that would show as additional HP...... that wouldn’t require the heads to flow any more on the flow bench.
                  Being fairly conservative, I’d say there was an easy 60-70hp left in that combo without reworking the heads any more.
                  That would put the hp/cfm level up around 2.5hp/cfm.

                  Brett Miller built a Victor headed 440” SBM a couple years ago.
                  Made over 1000hp with heads that flowed under 400cfm.
                   
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