All the 90+ manifolds that I have examined have been cracked.

The two most common places they crack are shown:

...on the left side, between #4 and#3

...on the top, between #3 and #2

The cracks in this manifold are not the worst I've seen in a 90+ manifold.

The lines I scribed are guides for grinding. For a Mitsu turbo, I will stay closer to the inner lines. For a Garrett turbo, I can go larger. Carbide burrs handle the iron easily.

The "cross" shape with a point at the back of the plenum is a "goilet". It is a shape that improves the merging of multiple flows into one flowstream.

The old style manifold has no goilet. That is a drawback: the flow from the runners are aimed at each other, not the outlet.

The goilet helps to merge the flows from the runners, and assists in directing the flow from each runner towards the outlet. Unfortunately, the outlet on a stock manifold is very small and restrictive.

As the porting progresses, the improvement in the directing of the flow will show itself.

The result is that the goilet will finally be used closer to its optimal effectiveness.