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Case porting


Bill

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I used a die grinder, first scribed the gasket lines, then used a carbide bit till i was close to my scribe lines. Then I used porting sanding rolls to blend it in and take it to the scribe lines.

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They say the gains are minimal, maybe 1-2 horsepower. The gains are probably larger the bigger the motor you have. But I had everything pulled down already, so every little bit helps.

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Don't have any dyno #'s to prove it, but from my experience it makes a difference in the bottom to midrange the most, but is a slight power gain accross the board. The intake charge has a smoother path to flow into the transfer ports so it maintains better velocity.

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Its not done to increase the size that much, what its done for is where the cylinder and the top case meet up do not match that well. There is a 1-2mm lip that blocks the transfer air from coming up. So basically all you are trying to do is take the lip out. You can feel it with your finger if you have it apart.

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Case porting is actually just gasket matching to reduce any flow interruptions, I think people are worried because cylinder durations and such need to be exact in order to benefit.

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