Just to add a little bit here, the Skyraider was definetly a dirty bird, but I would like to add the T-28 Trojan to the list as a very dirty spewer of foul black soot. That black stripe painted from the cowling over the wing root wasn’t for decoration. I spent many hours on the washrack at NAS Whiting Field trying to scrub that carbonized crud off of the fuselages of many T-28s.
The waste gates on B-24s and B-17s were electrically controlled w/a manual overide, a reostat that allowed you to dial in the amount of boost you wqnted. If the controller failed, the wastegate usually went to the fully closed position (full boost) - which led to problems if it failed during takeoff or if you had to make a go round during a landing. Going to full boost below 10,000 ft would cause overboost which could cause distruction of the engine rather quickly (you literally blew the jugs off the engine). If you were aware of the problem, you could control the boost w/the reostat or by carfully adjusting the throttle lever (either of which was a pain in the butt according to the pilots who flew the B-17 we operated as an air tanker). In our operation the system was always left on.
Here we go, I knew I had this diagram somewhere. The waste gates (14) are clearly part of the engine exhaust system. Exhaust gasses are collected in the ring and sent back to the turbo, with the watse gates serving as something like overflow dispensers:
