Gasket match- worth it??

Small Block Mopar Engine

  1. mopowers

    mopowers Well-Known Member

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    I've got a 340 that I'm doing a top end swap on. I'm getting ready to install a set of RHS heads but I'm curious if it would be worth my time to completely disassemble them in order to port match them to my RPM airgap intake. Do you guys think it would be a waste of time for a 340 street car?
     
  2. Bad Sport

    Bad Sport HALF A BUBBLE OFF Staff Member FABO Gold Member

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    From my limited knowledge, it's my understanding that if the port size is larger on the intake it can cause turbulent air as it progresses into the heads from hitting the shelf that surrounds the ports.. If the intake ports are smaller than the head ports not as big an issue.

    If you do gasket match, it's recommended that you follow the match down into the head a bit to create a smooth transition. You have to be careful not to take to much and break through.

    Hopefully someone will chime in and correct me if I'm off base here.

    I have done tons of reading on the subject as I have a set of J heads I'm going to port in the near future. (fingers crossed, lol)
     
  3. rumblefish360

    rumblefish360 so close yet so far away

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    No, I don't think it a waste of time though the power return would be small. Though every last little detail adds up for more power and a better running car. I like the idea. No fuel crashing, puddling, creating fuel droplets that are hard to burn.
     
  4. 4spdragtop

    4spdragtop FABO Gold Member FABO Gold Member

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    Subscribed....Im going to do this to dads 273 with Ld4b and stock heads
     
  5. EL5DEMON340

    EL5DEMON340 Well-Known Member

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    most aftermarket manifolds i have done have a ton of core shift and are way off i always do it.
     

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  6. krazykuda

    krazykuda FABO Gold Member FABO Gold Member

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    If you study fluid dynamics, you learn that any sudden expansion or contraction in the flow causes a loss in flow energy.

    When the intake runner is larger than the head port, then the air runs into the wall and gets "backed up" which will interfere with the flow slowing it down.

    If your intake port is smaller than the head port, the sudden increase in area causes the air flow to slow down also.

    It's best to match it as good as you can for optimum flow.

    VELOCITY = TORQUE when talking about intake flow.


    Sure, it's minimal, but we are all trying to squeeze every last horsepower out of our engines that we can....


    If you want to waste horsepower, you could always run two A/C compressors.... LOL!
     
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    • jerry6

      jerry6 Banned

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      Free HP , always worth it !
       
    • Prine

      Prine A-Body Fanatic

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      x2

      every little bit of "free" cfm counts.
       
    • 273

      273 Well-Known Member

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      While you got them apart you should clean up any casting flash and parting lines in the bowls and I would port match not gasket match. Plus you double check all the valve and spring clearances.
       
    • mopowers

      mopowers Well-Known Member

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      They are freshly assembled from the engine shop whom built them. Just not sure it would be worth spending the time breaking them all down if any HP gains would be small. I guess I'll have to check the ports and gaskets to see how off they are.
       
    • 273

      273 Well-Known Member

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      It's up to you but I'd do it if you pick up 5-10 cfms gives you the same benefit as going one step up in cam size without any of the negatives of a larger cam or you could drop a size and gain a more streetable package without a loss in power.

      After your basic cam header and high rise every hp is a struggle and an expense.
       
    • 4spdragtop

      4spdragtop FABO Gold Member FABO Gold Member

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      Can you expand on the differences and the benefits??
      Not being a smartass, Im doing something....just dunno what yet this winter...maybe??
      Its on Dads 273, and an LD4B is in the works.....

      Thanks
       
    • WRB426

      WRB426 Insane 4 Mopars FABO Gold Member

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      I would like to know the difference between the two please. I always thought it was the same thing just different wording.
       
    • 273

      273 Well-Known Member

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      Port matching is you take only enough metal to square and match up the ports
       
    • Hemioutlaw

      Hemioutlaw Well-Known Member

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      Excellent example ☆
       
    • EL5DEMON340

      EL5DEMON340 Well-Known Member

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      To bad I couldn't find my holley strip dominator pics, they were real bad!
       
    • krazykuda

      krazykuda FABO Gold Member FABO Gold Member

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      Yep, Holley had the worst core shift that I've seen on those... :violent1:
       
    • autoxcuda

      autoxcuda Well-Known Member

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      My M1 intake. We put alignment marks on the intake and head because there can be some slight shifting between the intake bolt holes.

      [​IMG]

      [​IMG]

      [​IMG]

      BEFORE

      [​IMG]
       
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      • mini

        mini Well-Known Member

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        I use a bore scope to ensure they match!
         
      • mderoy340

        mderoy340 Well-Known Member

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        pack the intake runners with coffee filters or lint free wrags. install old valve cover, tape off exhaust/water outlets, tape off bottom off head and start cutting. use a shop vac to clean up and your done.
         
      • crackedback

        crackedback FABO Gold Member FABO Gold Member

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        I wouldn't because you have a fresh set of heads in ready to install condition. How do you plan to clean them properly and reassemble. Are you going to ruin the valve seals in the disassembly process.

        From your current starting point, for the potential gains, IMO, it a waste of time and effort.

        Maybe ask the shop that put the heads together for you. :)
         
      • 75DartSE

        75DartSE Well-Known Member

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        It really depends on your intake. My old school performer intake ports were half the size of the EQ Heads. I worked away at the intake and eventually found that about 1-2 inches in, the runners widened right up to the size of the gasket, and the intake ports on the head. So in my case, I think it was totally worth it, but maybe a newer style better quality intake may not require all that work.
         
      • 4spdragtop

        4spdragtop FABO Gold Member FABO Gold Member

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        Can someone explain how to do a port match please?
         
      • moper

        moper FABO Gold Member FABO Gold Member

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        Gasket matching IMO is easier and more consistent. That's what I do.
        1. Make sure the intake fits properly. You want the final machining all taken care of before you start.
        2. Use the gasket you will use on final assembly. For LA mopars with LA or Magnum heads I like the Mr. Gasket Ultraseals.
        3. Use Dykem/Prussian Blue or similar marking compound and "paint" the intake flange (head and intake).
        4. align the gasket with the intake bolt holes and tape in place or bolt lightly in place (without compresing the gasket...)
        5. Scribe around the inside of each port opening.
        6. Remove the gasket, leaving the scribed line in the marking compound.
        7. Remove material at the opening to the scribed lines. Do not go beyond the lines!
        8. Blend the new opening back 1/2-1" into the port and smooth any transitions/corners.
         
      • AJ/FormS

        AJ/FormS The end is near FABO Gold Member

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        For street, Im with crackedback. Esp. if your combo can already blow the tires away. I mean 1st gear can pretty much get you a speeding ticket.
         
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