decat on the 170 does make them way too noisy for my liking, and as for induction kits also never been a fan unless enclosed with high flow cold air feed isolating them from under bonnet heat soak or they run crap in warm weather or high running temps, if planning more engine mods then maybe a aftermarket ecu with various maps, people like MSD are best to speak too, just stay well clear of jamcock in northampton