The Dubach Racing Development (Dr. D) exhaust systems increase power throughout the RPM range.  The unique attributes of the Dr. D's Step System allows 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 gives a crisper throttle response from bottom to top. The key advantage of the Step System is improved low, mid and top end power. Rejetting is not required, and the Dr. D exhaust systems meet the AMA 102dB sound level requirements.