The Akrapovic Racing exhaust systems with their hexagonal mufflers are the top of the line product for this motorcycle, and are designed for riders who know how to get the most out of their equipment. The increases in power and torque can be clearly seen from the dyno measurements and clearly felt on the motocross track. The muffler includes a noise damper for the European market, and an approved spark arrester for the US market. Measurements of the Akrapovic Racing system on the YAMAHA YZ 250F (with muffler insert): Power & Torque: the Akrapovic Racing systems provide the increased performance that top riders are looking for. Engine performance is increased throughout the entire rpm range. The power curve is steeper and smoother, and the increases are highest in the low end and the top of the range. The torque also gets a major boost, which will make riding smother and lower your times on the track.