Hello all, It seems like I'm one of the first to install a new factory 4.1 on my 04 450f. I've only started the bike a couple of times to check for leaks but I can tell you that throttle response is faster and it's louder with the trottle really opened up. At idle and with little blurps it's not too bad for a much shorter unit. I'll be able to give a full ride report next week. BTW it's the slip on annodized set up.