I mark the flange with a T3 gasket to give myself the borders for the porting work. The heavy scribing is the actual size of the gasket opening; the outer and inner lines scribed give me a max and minimum boundary, and supply a reference to keep the grinding even.

The objective is not just to make the outlet larger. It is to enlarge the opening to improve the flow from all four runners of the manifold into the turbine housing. Removing metal that obstructs the flow is only part of it; compensating for the different characteristics of each runner's aim and angle is the other part of the plan.

I start out by removing iron to the minimum lines, basically going straight in. Then, I remove more iron to shape each runners outlet. And finish up by blending the pairs together.