The unique attributes of the Dr. Ds step system allow for a more efficient intake stroke. It does this by resisting the reflective exhaust pulse during the intake / exhaust overlap. In plain language, the carefully tuned steps in the system allow for a lower net cylinder pressure, which gives a crisper throttle response from bottom to top. The key advantage of the Step System is improved low end response with substantial gain in the mid and top ranges. Dyno tests show a 3.6 horsepower increase at peak. The Dr. D Spark Arrestor System is designed for riders who are looking for the same extraordinary performance characteristics of the Dr. D Race System, but also need to quickly adapt the system to meet USFS spark arrestor and/or noise level requirements. The DR. D complete exhaust system is birthed from Doug Dubach, who brings years of experience to the motocross and supercross scene. DR. D constructed this complete exhaust system with an aluminum muffler in conjunction with a magnesium end cap to reduce weight and stainless steel head and mid pipe to provide long lasting durability. DR. D welds the stainless steel mid pipe to the aluminum muffler to eliminate weak points and excessive weight in the exhaust system that spring connections can cause. To create a solid mounting point DR. D uses a CNC billet hanger on the extruded aluminum muffler sleeve. The magnesium end cap on the DR. D complete exhaust system is easily removable to access the spark arrestor screen. With the spark arrestor installed the exhaust system meets USFS approval. Repacking the DR. D aluminum muffler is simple with the removable bolts on the lower end of the sleeve. The DR. D complete exhaust system includes: aluminum muffler with stainless steel mid pipe, stainless steel head pipe, USFS-approved spark arrestor.