, separate wastegates independent of the turbine housing are only called external, not divorced wastegate. "divorced" simply means that the 2 outlets from the turbo exit through separate (or "divorced") pipes, which is true of divorced wg downpipes.
For the most part, I agree with mosc. There is little gain, if any, over a bellmouth downpipe. However, the CONCEPT of divorced is actually really good. The problem is the execution. Imo, there are 3 major problems with divorced wg downpipes.
1. Internal wastegates NEVER open all the way. At most, the wastegate "door" will only open at a 45 degree angle. This means that, instead of all the wastegate gases flowing right into its designated piping, most of the air hits the wastegate door and changes direction, running RIGHT into the dividing plate.
2. Since the dividing plate is not completely sealed, some gases are allowed to cross over into the turbine gas area (defeating the whole purpose of divorced wg), while the other gases swirl around the turbine housing until they find their way down the wastegate piping.
3. The inlet for the wastegate gases is small, and not located at the area of direct flow of the gases.
SOLUTION: this setup, while not ewg, would be truly divorced.
1. A turbo with a turbine housing that separates both outlets (such as aps turbos)
2. A downpipe with an outlet that encompasses the entire wastegate outlet (such as the aps downpipe)
3. A downpipe with a wastegate opening like the aps' that slowly tapers into a pipe, then is routed back into the downpipe further down the exhaust path (like the bpm)
You can probably tell I've thought about this a lot. Too bad downpipes like that don't actually exist... sigh. They would be expensive to make, but would definitely make more power than a bellmouth (with the right turbine housing).