What does anyone know about the factory 4.1 titanium from FMF? Power bomb or mega bomb make any difference? Are people happy with slip ons or do you need to spend the money for the full system? (for the 07yz450f) I have the TI FMF Powerbomb with factory 4.1 system and I love it. It makes the bike have way more grunty, bottom end power and sounds awesome. I am looking to get the megabomb if I can find one on ebay. In one of last months magazines (I think MXA but not sure) they test rode the 2008 yz450f and added the megabomb/4.1 system and said it really helped. So I would figure on the 07, which dosent have a bottom end problem (from what I have read on here) the system would do wonders...good luck!