Yep Ive got a piperX ind. kit and it is well loud although i have reservation about power gain (it might be a loss), it does whistle and when you switch the engine off, it continues to make a whine for a second or two.
Ben, what did you go for after taking you r one off, i.e. what seems to be producing the goods, and did you ever have cold air ducting to it
Alex M