All HKS exhaust systems are engineered with performance, quality, and value as primary goals. Through countless comprehensive efforts of flow analysis, dyno testing and tuning are we able to maximize horsepower gains throughout a board powerband, while maintaining reasonable sound levels for street use. HKS Exhaust Systems that are designated for street use retain all factory emissions equipment and conform to 95-decibel exhaust noise level limit. (Note: Some HKS exhaust systems are designated for Off-Road Use Only and are solely to be used for Off-Road purposes)