Im not sure if im just over analysing some slight noises that may have been around for a while, mabe its due to the Z not being my daily anymore. As for the S/C the Vortech seems to make more power(larger) than the HKS one so thats my reason for going for it. Im not after a tuner kit just want the whole package including fueling; larger injectors, fuel pump etc. Have the time and spare car to fit the kit myself so just need to find a UK supplier....... and the £4-5grand