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Horsepower potential based on cylinder head flow

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  • Horsepower potential based on cylinder head flow

    Does anyone know of a formula or a link to a formula to establish the horsepower potential of a cylinder head based on CFM of airflow? I realize volumetric efficiency, cylinder sealing and other factors come into play here, but I am just looking for the numbers based solely on airflow.

    Thanks,

    Ron
    It's really no different than trying to glue them back on after she has her way.

  • #2

    Re: Horsepower potential based on cylinder head flow

    Re: Horsepower potential based on cylinder head flow

    As a VERY ROUGH GUESStimate, you can go 2 times peak flow.

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    • #3

      Re: Horsepower potential based on cylinder head flow

      Re: Horsepower potential based on cylinder head flow

      As a VERY ROUGH GUESStimate, you can go 2 times peak flow.
      Thanks, DF

      So...

      If an intake port flows [email protected]" lift it can be ROUGHLY GUESSTIMATED the engine can produce 630HP naturally aspirated?

      Ron
      It's really no different than trying to glue them back on after she has her way.

      Comment


      • #4

        Re: Horsepower potential based on cylinder head flow

        Re: Horsepower potential based on cylinder head flow

        Way to many variables to give any kind of a real number but if you want to play around here is one that I have from a posting on speedtalk. I just ran this against the flow numbers on my 4 cyl import motor and this actually came pretty darn close --Seriously within 2HP --- Go figure. :


        hp=0.25714 x cfm x #cyls. Cfm is at 28".

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        • #5

          Re: Horsepower potential based on cylinder head flow

          Re: Horsepower potential based on cylinder head flow

          Which in Ron's example is 649hp, or by very rough guesstimate, the same answer as 2 times the flow (for a V8). This is bench racing at the extreme, though.

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          • #6

            Re: Horsepower potential based on cylinder head flow

            Re: Horsepower potential based on cylinder head flow

            Fair enough, guys! Thanks for the help.

            Ron
            It's really no different than trying to glue them back on after she has her way.

            Comment


            • #7

              Re: Horsepower potential based on cylinder head flow

              Re: Horsepower potential based on cylinder head flow

              Us Aussies use the term all the time and I can't stand it. "These heads flow 600hp" they'll say.

              Why don't we just say they flow 280cfm @ 0.600" or whatever. 280cfm @ 28in/Hg is rigid baseline with few variables. Unlike a HP flow rating.

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              • #8

                Re: Horsepower potential based on cylinder head flow

                Re: Horsepower potential based on cylinder head flow

                From a lot of reading it's not only CFM, but velocity that will determine the HP output of the engine though?

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                • #9

                  Re: Horsepower potential based on cylinder head flow

                  Re: Horsepower potential based on cylinder head flow

                  IMO the 2x peak flow is ballpark like DF said.

                  I also like to look at minimum port cross-section too. If you plug David Visard's LVP formula into a spreadsheet you can calculate what size port you need to maintain good velocity without the port becoming a restriction. The best flowing port that is properly sized for the engine size and RPM should make best power and have good driveability.

                  If any of you guys want to play with my spreadsheet just shoot me an email [email protected] There are some other good formulas in it too (at least I think so)

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                  • #10

                    Re: Horsepower potential based on cylinder head flow

                    Re: Horsepower potential based on cylinder head flow

                    How would modify the formula for calculating (actual) flow under boost or blown?

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                    • #11

                      Re: Horsepower potential based on cylinder head flow

                      Re: Horsepower potential based on cylinder head flow

                      None of it is "actual" flow. The flowbench is just an indicator of only one variable of performance potential. People flow heads alone, then flow intakes alone, but bolt them together and you get another answer altogether. Now put a running engine under them and its all different again. Flow at 28" of drop can be used to estimate flow performance under boost since boost is just like flowing at a greater pressure drop. It gets more complex when you consider velocities, etc.

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                      • #12

                        Re: Horsepower potential based on cylinder head flow

                        Re: Horsepower potential based on cylinder head flow

                        Just for purposes of discussion, how about a ball-parky (theoretical) guesstimate on:

                        "How would adding one atmosphere (atm= approx.14.7 psi)

                        affect a head flowing 280 cfm @ 28-degrees drop?"

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