Wondered if I am right to use the word ports for a four stroke head but this is what I would like to know. Will a polished port increase air flow but causes a reduction in turbulance resulting in poor Air/Fuel mixture? Please advice. many thanks in advance.
The suface texture of the port has nothing (let me repeat that) NOTHING to do with the mass air flow in the ports on any current model four-stroke. You could glue M&Ms into the front of the port and barely get a blip on a flow bench. The air in the straight part of the port will just slide around them because the air nearest the surface is pretty much stalled anyway. The air travels much faster as you get closer to the center of the port (on round ports) . Porting is done within about 1.5 inches of the valve on either side of it. Anything done to the surface texture farther back up the port is just for looks. The real work of porting is rarely seen by the customers because they tend to get the head back with the valves already installed. So all the cool stuff that really gets a port to move air is hidden.
Exhaust ports can be fully polished. Intake ports have been shown to benefit from stippling (like the surface of a golf ball) on the outside radius.
Various theories exist on the use of rough versus polished port surfaces. Search around for information on racing car engine building. Four-stroke technology is generally universal.
But it does nothing positive for airflow. People routinely polish exhausts in the hope it will eliminate carbon build up. In my experience it fails in that regard as well.
The problem is, in an attempt to get a high polish in the port people often times make the surface of the port wavy which has a measurable NEGATIVE impact on flow. There is no solid evidence that polishing has any positive effect on airflow, but it's easy to measure the changes when the surface gets too wavy. 25 years at the flow bench has taught me that most of what I learned/believed/assumed about airflow while reading hot rod magazines was flat out wrong. :thumb:
There we go with the M&M's thing again...
Plain or peanut?
You would have a hard time justifying your time hp wise by rubbing on the ports of your XR-l.
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