Added the Stainless FMF Hi-flo header to my FMF Powercore 4 slip-on today. **(Edlebrock, open side panel and airbox) The good: - way lighter - much, much, improved throttle response above 2.5k rpm - slightly faster reving - now getting lean 'pop' on decel, meaning I can richen the Edle a bit - very clean, tight, sano fit and finish - very slight improvement in over-rev The bad: - the header leans in toward the rear tire more, and I will have to tweak it a bit, along with the muffler, as the muffler hits the tire right now - lost the first bit of 'ultra-grunt' bottom end. There is still plenty, it was just cool to be able to wheelie from a standing stop with no clutch.... Overall: well worth it in throttle reponse alone. Now I can dial power with the throttle like a CRF does.