When doing the 90+ manifold upgrade, I like to port the turbine housing inlet and the wastegate port to improve flow. On the Streak's Garrett T3 [stock size for a 240T, with watercooled center section], I actually did start the porting work. When I got to the part of the work concerned with the wastegate port is when I finally realized that there was a real problem; not just the 'usual' cracking.

Turbine housings see a LOT of heat. That is the normal condition. Because of the design of the casting, there will be expansion stresses inside the casting: the thinner portions of the casting heating up and trying to expand faster than the thicker areas of the casting. Similar stresses, but in reverse, are encountered during cooldown.

Stresses lead to cracks. Essentially, it is an unavoidable condition.

BUT, improving the flow through the system...the exhaust manifold, the turbine housing, and the piping of the exhaust system...via porting of the various components and via going with larger diameter piping, can reduce the amount of heat buildup...the retained heat...in the turbine housing and the exhaust manifold.

Reducing the levels of retained heat will also reduce the heat stress; which will reduce the stresses that cause the cracking. Parts will last longer.

It is NOT heat that turns the turbine wheel: it is FLOW of exhaust gases that turns the turbine wheel. Reducing restrictions to flow therefore gives two benefits: longer component life, and better performance.

This gallery is about my mistake: I spent time working on a turbine housing that was scrap, before I realized that it was scrap. My screw up: a costly one time-wise.

I did the gallery to show what to look for; so that others might benefit from my error, and not repeat it.