The induction for the pd130/150/160 is very deceiving! When you get to the top of the pipe and through to the maf sensor it's a large 80mm pipe work. Where if you follow the pipe down it starts to into a pancake shape to 'save space' to around 30mm or less. It does have to get smaller to fit to the turbo of course but it gets thin and very restrictive very quickly where it could be bigger and less restrictive, it's a big weakness and a poor design worth thinking about!
I have designed an induction kit from turbo which goes from 60-80 which is much better. Can feel the difference. So whilst everyone is thinking cold air feeds and such near the top it doesn't make much difference because the bottom is restricted