"Starting Line Products Performance Slip-On Slip-On Muffler by Starting Line Products This slip-on silencer for the Polaris XP 900 RZR delivers an additional 3 horsepower with well over double the airflow compared to the stock silencer. This translates into a substantial performance increase and better throttle response. Its stainless steel construction provides excellent strength and durability. The sound level measures 95.5 DB (at 4200 RPM) using the SAE J1287 sound test.