Dazz, i'm not sure but just thought i would point out, it would be a lot louder on a petrol model as the turbo also muffles a lot of noise. also from experience would not see a great gain in HP maybe a gain in economy, and a loss in low end Torque. on a petrol model extractors show the best gain.
but on another note since i got back from my trip out west this past weekend i have noticed i used more fuel than i was useing driving fast with the same type exhast as you are selling, i think there is a ecomony gain with that pipe, but i have the stock system on now. i'm not selling my pipe.