improving tdi mpg

[Benspickup]

Hello, I've recently bought a 110 station waggon, with a 300 tdi in it. Its all in reasonable order but as ever , i am keen to get the best out of it.. I've taken off the fan and removed the cat down pipe. My new one though has a dent in it, prob reducing it to 2 thirds diamiter. Is it worth changing to improve mpg and what else can be done? Thanks for your help!