First of all why do you want to fit a dump valve to a TDi? Is it for the sound or for performance? If its performance then don't bother because it will have an adverse effect on your performance. If its for sound you can achieve a reasonable effect with an electronic dump valve but this will cost you up to ?300. Its not something that's really worthwile imo but depends on whether you have money to burn or not. Do a search and you'll find some information in this forum.