For sure I wouldn't use anything but NGK or Denso. I think the stock plug for most of the ZX-6Rs is the NGK CR9E. They make a dual electrode version of this plug called the CR9EK that may make a little more hp but cost about twice as much. I am using these and they work well but I couldn't truthfully say one way or the other on the hp issue. There is also an iridium version of the CR9E as well as the dual electrode platinum CR9EK that is used in the ZX-12R.