I have a 2.0 DTi mk4. Been looking into modifying the performance but it seems there is not much out there.

How much does a remap cost and what sort of gains should I expect from it?

And how else could I modify the car performance wise?

Also, does anyone have a back box on their 2.0 DTi that is fairly loud? My Irmy box is silent so I'm looking to get a better one.

Does the centre section from a petrol fit the DTi?

Last thing; Does anyone know whether a dump valve will damage my engine at all? I've only read that it doesn't make sense on a diesel, but is there any damage caused by it?

Thanks in advance.