Being a cheapskate, ive decided to go down the DIY route and make my own snorkel - what diameter pipe should i use for a 200tdi? 2 1/2 inch or 3? thanks steve

To quote from a website that i have forgotten where from... a 2 litre engine at 5000RPM uses 100 litre of air per second... (a lot.) I would suggest because of the length of the pipe, as big as you can get away with, and definitely no smaller than the inlet manifold.