Would anyone happen know if the inner part of a link pipe (here being the factory 50mm link pipe from a 998S) is supposed to look like this at the inner part of the welding or has that cavity been created by corrosion? I’ve thrown a flashlight beam from one end of the pipe to show the cavity in the pics.
Afaik the pipes are open internally at the point they are welded together, ie the gas from one cylinder hits the link pipe and can flow into either exhaust, so yes, it’s normal. This is the point where the exhaust pulse can expand causing a drop in pressure which assists in pulling the new charge into the cylinder due to a slight overlap between inlet valve opening and exhaust valve being fully closed.
