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Old 12-01-2014, 08:15 PM
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Originally Posted by Fabroman View Post
That looks pretty good, nice job The most important part is to remove that hard edge where the port changes direction...
Yep, blending the short side radius is crucial. That sharp edge creates turbulence which causes the air/fuel mixture to start tumbling and restricts airflow of the port. You don't want to go too much though, because going too big slows down the velocity of the airflow in the port. The key to a successful port is keeping from having sudden changes in port area. In theory, the cross section of the port at the short turn should match the port size closely.

One thing to remember with any port work is that the port needs to meet the application. IOW, you don't need a high flowing, big volume port for applications that are going see to a lot of start and stopping, and part throttle running. In fact, you can easily hurt performance on a fun kart by going too big because you slow port velocity and kill the bottom end. A lot of people hog a port out and stick with a stock cam/springs, and that is pointless. For most fun kart applications, you want to remove all rough casting areas, enlarge the bowl slightly and blend the short side radius. You can open the port entrance slightly, but in most cases, that's the last place than needs attention, and that's the first place most amateurs start porting. I can't tell you how many times I've seen old flathead blocks ruined because somebody hogged the crap of the port entrances, and never touched the bowl or short side! -lol The same thing is common in automotive heads that have been butchered by somebody that didn't know what they doing.

On high RPM race engines, you need a totally different port than you do in this kind of application. Race engines running at sustained RPM are not have hamstrung by needing the higher air speed and low lift flow numbers that your common fun kart needs.
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