Hey Peoples! Im telling ya I have had a lot of different exhausts in my days of riding but this MRD exhaust is hands down the best Ive had yet (especially for the cost, its one of the cheapest! ) I run a stock 2006 YZ450F, The best bike Ive ever had, I wont do too many mods to this engine cause Id be a fool to say it needs more power, I just wanted to change the power curve of the engine and make it crisp/snappy throttle response and dial in the suspension and put guards everywhere to save the bike from a guy like myself who is prone to high speed crashes now and then. Anyway, here are the differences this exhaust has made when combined with a fuel screw, boyeson quick shot 2.... Very very crisp throttle response and almost ZERO bog Ease of starting when engine is cold. Low end torque is waaaayyy stronger and the "THROTTLE BLIP" is fantastic for last micro-second corrections when jumping. Mid power seems more agressive Hi Rpm power seems the same- no change Looks trick and sounds very aggressive. You get a cool warranty too that if you ever bend/break it, MRD fixes it for free! My friends say that I am a much faster rider cause the bike is soo dialed in and I use the power much more effectivley. I also got a confidence boost from the new power curve/throttle response to take on more difficult situations with authority instead of hesitation or slowing down. Anyway, the best $399 Ive EVER spent!