PORT VOLUME-IS BIGGER BETTER OR IS LARGER LESS? Richard Holdener

Small Block Mopar Engine

  1. 273

    273 Well-Known Member

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    • Wyrmrider

      Wyrmrider Well-Known Member

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      shape and velocity is better
      bigger can kill your low end = flat spot
      so unless you trailer and run high rpm only...
      same with big valves, big cam , big compression
      all have to work together
       
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      • RustyRatRod

        RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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        I go by what Jim Laroy has always said. The shape is what's important.
         
      • Krooser

        Krooser Building Chinese Free Engines since 1959...

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        Geez that guy is annoying....
         
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        • B3422w5

          B3422w5 Well-Known Member

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          More port volume for big inches
           
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          • MOPAROFFICIAL

            MOPAROFFICIAL FABO Gold Member FABO Gold Member

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            Depends on the rpm window and wether or not you built beyond the heads sweet spot. 'Like a 4" arm" Most stock heads can grow 15cc and 9nly make more power even if they flow 'about the same'.
             
            Last edited: Oct 6, 2020
          • B3422w5

            B3422w5 Well-Known Member

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            Anything W5 and below was pretty much designed for stock stroke, or at most, a 3.79 arm.
            The advent of 4 inch plus arms left such stuff wheezing in serious even bracket level builds on the big end of the track, especially non offset stuff like eddies, Trick flows, etc
             
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            • MOPAROFFICIAL

              MOPAROFFICIAL FABO Gold Member FABO Gold Member

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              302 based motors come with heads that have smaller ports than a 318. This example is really just about useless to any of us...and they went over the factory designed port volume by ...oh 55+cc!?
              They basically went from changing to an ideal performance head from stock..to a head that belongs on a 351 or 400cid.

              That is called purposeful blundering for the sake of the argument to make a point that's really tired and common knowledge.
               
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              • yellow rose

                yellow rose Overnight Sensation

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                100% FACT.
                 
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                • B3422w5

                  B3422w5 Well-Known Member

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                  One NICE thing about about long stroke, small heads...
                  1/8 racing becoming the norm has masked that weakness to an extent.
                  I know the 418 with eddies i am putting in my Dart will “ seem” to run much better in the 1/8 than it will in the 1/4.
                  Block of wood.... meet under the gas pedal
                   
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                  • 273

                    273 Well-Known Member

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                    I feel obviously port volume, velocity is important but like everything people take it some times too far especially with basic builds. With SBM there's not too many 200 plus cc heads so port volume ain't a huge issue, generally only comes up when people talk about doing 318/273. I think the tunnel port 302 boss ford has scared everyone especially with small displacements running even reasonable sized ports.
                     
                  • 273

                    273 Well-Known Member

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                    Obviously there was no need going bigger than the 190 cc heads didn't really gain but on the dyno didn't really lose, don't think it was meant to be super scientific just he we have these heads and and short block lets see what happens. Lots of his dyno runs are from years ago and he just try's sometimes to see what different conclusions he can come up with the data. But to It does show ya the 190 cc where the best fit for the 302 and probably the strongest runner but I don't think the other two would of been slugs.
                     
                  • gregcon

                    gregcon Well-Known Member

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                    I'm not saying port volume has no bearing....but it's over-emphasized. The engine doesn't know that the cylinder head ended and the intake manifold started.
                     
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                    • krazykuda

                      krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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                      A great head flow guy once told me, "Velocity is torque"....
                       
                    • MOPAROFFICIAL

                      MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                      the bigger head was down in the mid-range but you're right might not have shown a difference at the track...who knows, might be just an efficiency issue.
                       
                    • gregcon

                      gregcon Well-Known Member

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                      W7 heads
                      W7 Intake port 258cc.jpg
                       
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                      • yellow rose

                        yellow rose Overnight Sensation

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                        I think my W5’s were 225 or close to that. The W7 is what I should have used, but at the time I couldn’t get them.
                         
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                        • 33IMP

                          33IMP Well-Known Member

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                          Which of these seems the most wrong?....
                          1. 408 mopar stroker with 170 cc. Rpm heads
                          2. 302 Ford with 225 cc. Cnc ported heads
                          3. 396 Chevy (big block) with 316 cc. heads, stock, that flow 325 cfm.
                          4. 440 mopar with stock heads that flow around 220cfm, if they are pretty good ones (215 cc.? 235cc.?)

                          ....
                          1
                           
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                          • yellow rose

                            yellow rose Overnight Sensation

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                            1 and 4.
                             
                          • rumblefish360

                            rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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                            4 then 1. But a lot has to do with what it is for.
                             
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                            • gregcon

                              gregcon Well-Known Member

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                              Back in the day, with my stock headed, stock blocked, stock cranked, stock rodded 440 I put an awful lot of guys on the trailer who had BB Chevy's with big old intake ports.
                               
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                              • turboking15

                                turboking15 Well-Known Member

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                                Big thing i take away from this demo is people want to say too big of a head kills low end power when in all actuality most of the power difference is less than 10hp across the pull, up until the point where the larger head pulls away in the upper rpms. Youll be hard pressed to find someone who can tell a 10hp difference by the seat of their pants. (Read 90% of the people on this board, myself included)
                                 
                              • yellow rose

                                yellow rose Overnight Sensation

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                                Yeah, the big R/S ratio helps with the undersized ports.
                                 
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                                • rumblefish360

                                  rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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                                  As mentioned by Richard, what is it doing at part throttle? I’ll never recommend the biggest head port as possible to use. Ever. The dyno is one thing, actually driving the car and how well it works is another.
                                   
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                                  • pittsburghracer

                                    pittsburghracer FABO Gold Member FABO Gold Member

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                                    There’s a reason hidden here why 351 Cleveland’s and 426 Hemis were dogs on the street.
                                     
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