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Head porting question????

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Head porting question????

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    Head porting question????

    Ok, i have been reading many articles on how to port a head since i'm planing to do it on mine. Most of the sites that i visited showed how to increase the port size and polish to get maximum flow. So i taught ok this is what i have to do. However, i stumbled accross a site that told people to do otherwise, meaning reducing the port size. He said that doing this would increase velocity and reduce negative fllow during the intake cycle of a four stroke engine. The guy seems to have done his research and adds that increasing the port size will cause too much gain during the intake cycle and therefore, will have negative flow before the valves are completely closed which will reduce power during the compression cycle.

    Anyways my qustion is: The guys or girls, who got there heads ported, did they get there ports enlarged or reduced in size? Was there a significant power gain by doing this project.

    P.S. The site where the guy talks about reducing the port size is as follows:
    http://www.mototuneusa.com/homework.htm

    #2
    I'm not sure if whether he's right or wrong but you do realize in the article he's talking about motorcycles right?

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      #3
      In the article, there is a picture of a 4 cylinder DOHC head which he is preparing and reducing port size. So im not sure what to believe.

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        #4
        Reducing port size does indeed increase velocity, but at what gain... you reduce volume. This needs to be balanced and you need to have a done many many heads to have a baseline with which to be able to compare results... just go to someone that has done this many times over, or stay with stock port sizes. Some of the big companys are just port matching then blending the port to the runner about an inch or so up the channel... smoothing out the exhaust and roughening the intake... three angles are enough.
        Out

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          #5
          Originally posted by Schu
          Reducing port size does indeed increase velocity, but at what gain... you reduce volume. This needs to be balanced and you need to have a done many many heads to have a baseline with which to be able to compare results... just go to someone that has done this many times over, or stay with stock port sizes. Some of the big companys are just port matching then blending the port to the runner about an inch or so up the channel... smoothing out the exhaust and roughening the intake... three angles are enough.
          Out
          This is the current trend. From the research that I've done it appears that a majority of the gains that are to be found in the valve job the importance is placed more upon choosing the correct throat and radius angles (on each side of the 45 degree angle that the valve actually seats on). My research has also led me to believe that basically the stock ports on our heads leave little room for improvement basically minor improvements for velocity increasements and like Schu said above you want texture on the intake side to aid in keeping fuel suspended in the air and for the exhaust to be as smooth as possible for obvious reasons.

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