Please note that my exhaust manifolds are already ported......did that a year and a half ago. I did a good measurement today before I left for work and created it to scale for this topic.
The full circle is the inside diameter of my exhaust manifold ports. 1.435". Area of 1.6"
The inside profile is my head port. The head port has a calculated area of about 1.2 square inches.
By matching the head port BUT KEEPING THE PROFILE (flats have a purpose), I can squeak another easy 15-20% in exhaust port flow from the heads. If I made it a full matching round (which I won't), I could gain 33%.
It'* better to take half what you WANT if you don't like creating scrap. The D-shaped exhaust port is designed to cancel out the shockwave that returns back to the cylinder from inside the exhaust manifolds. This actually helps performance.
So I'll be enlarging the rounded sections in WIDTH, but leaving the flats where they are.