Hi,
Has there been any instance of putting in performance headers & mufflers for diesel cars , moreso for a swift DDIS ... I believe as it is the compression ratio for diesel cars is quite high, by fitting in a header for a DDIS engine, do things really work ? Also, once the header is fitted in, does it make sense to put on the muffler ?

Throttle

I don't think this combination will work for diesel cars and it might affect the performance and it doesn't make sense putting a muffler or any muffler parts.

Hey mate!
Many people do not prefer such mods for diesel vehicles.
Even if they put mufflers, it is not worth as you will not be getting the output expected.
Do think about getting a remap or put a diesel tuning box.
"PETE's" company is doing pretty well in these tuning box stuff.
Cheers!