Originally Posted by
Tim Williams
They are prone to cracking there on the casting line but far from all of them crack. Excessive heat seems to be the main cause of them cracking, a poor remap with a standard intercooler and exhaust are about the best ways to crack them. once the crack goes through to the side facing the turbine wheel it WILL give reduced performance as gas will have a free path bypassing the turbine wheel.
The first place to look at once they crack is the the sealing area for the wastegate flap, if it's darkened one side of the crack it's scrap as the wastegate won't seal. If it's the same both sides of the crack it doesn't mean it be worth fitting as it may only last a very short time.