HKS Sports Cat Back Exhaust 1988-1991 Honda Civic Hatchback Si LES-H05HKS Sport Exhaust Systems are designed to reduce backpressure and increase exhaust flow for greater peak power and a broader torque band. Each Sport Exhaust application utilizes a specific muffler design and shape along with the appropriate piping diameter to maintain low end torque while maximizing high end horsepower for your 1988 1991 Honda Civic Hatchback Si. Piping diameter 50mm Tip 60mm Tip Style R 2