I think HMF is the way to go (full system).I used Yoshi's Vance & Hines on my street bikes But i NEVER got 1 on 1 support as i have with HMF. they are a small company,and dont mind talking you through things, hell i had JOE at HMF walk me through the Jetting process. Top that YOSHI???i have dealt with yoshi/Hines before and NEVER had anybody remotely interested in helping.
PS HMF has a great RED pipe for your white YFZ450 and the power is KILLER!!!
The HMF is nice, but the TC will give you the most low-mid power which is what you want for MX. The White Bros are nice but will not give you the power the others will. I think the GT Thunder is supposed to be good as is the Dr D but I havn't heard much about either one. Well thats my .02 and hope it helped.
The California State Parks Off-Highway Motor Vehicle Recreation Division has been testing noise emissions of motorcycles and ATV’s for about a year. This information can be used to help enthusiasts find a muffler for their OHV that will comply with California’s noise emission standards. Only tests with a reading of 101 dBA or less are included. The list is by make, model and year of the OHV tested.
2003 Honda CRF450 - Pro Moto Billet spark arrester without quiet insert - 96.4 dBA.
2003 Honda 400EX - stock exhaust - 87 dBA.
2003 Kawasaki KLX400 - new series FMF Q pipe - 93.5 dBA.
2002 Yamaha WR426 - original FMF Q with quiet tip - 95.4 dBA, Supertrapp IDS2 with 5 disks - 99.8 dBA, Silent Sport Racing Muffler - 90.4 dBA, stock exhaust with GYT-R tip - 90.0 dBA, stock exhaust with Pro Moto Billet insert - 91.8 dBA.
2003 Suzuki DRZ400S - new series FMF Q - 89.9 dBA.
whatever you do, do NOT overlook the baldwin pipe. mark has been working on the yamaha fourstrokes since they came out and he knows them extremely well. i have a baldwin after alot of one on one talking and riding with buddies at the races( cross country) and went with the baldwin. mark will work with you through everything and everything and treats you like a priority and will call you back to make sure and the power.....well, i have not been beat bye anything yet and thats a fact. also the low and mid grunt is amazing and even the top end is enough to give even a seasoned ridier arm pump. i ride 3 to 5 days a week hard core in the woods. and not the same trails, hill climbs- i travel to wellsville on a reagular basis for those and they dont get any bigger. i have been extremely happy with the performance,looks and the support from the baldwin shop. mark is a top notch guy to deal with. and there's nothing like leading a pack of 40 to 50 machines into the woods on a regular basis. dont overlook baldwinmotorsports.com