The exhaust port porting is dead simple.
You want to make it a "D" shape with the flat edge on the top. Wider is better but wears the rings.
More radius to the top, the longer the rings will last, flatter gives more pipe response.
Do not touch the bottom of the port other than to clean up the sleeve window transition.
1mm is recommended, 2mm will make it a screamer, 3mm will hurt torque without other mods.
Shape and height are more important than polish. Don't take too much metal off.
This is a stock intake port with a piston in the cylinder:
The intake skirt on the piston is very weak so don't narrow the center bridge but match the two as shown.
Radius the back of the piston bridge to the center on the inside of the piston only.
Radius the cylinder bridge ROUND to the airflow. Do not knife edge it. (not shown here)
Widen the sides of the cylinder ports as much as you dare, angle (not radius) to the center of the piston.
Match the sides of the piston with the cylinder port by angling to the center axis of the piston
To increase window height take metal off the top of the cylinder port and the bottom of the piston window.
My preference was to fill the intake with epoxy after widening:
A bit rough but it was a preliminary experiment on a worn out cylinder. Ran great.
Another experiment was a top port in well worn piston before we replaced it:
This worked well,
This did not:
Oh well, we tried, we learned. More of a good thing is not always better.
Steve
