Some of the exhaust systems we have include an H-pipe or an X-pipe because adding such a pipe to a dual exhaust system has been proven to unleash more horsepower. When two close firing cylinders are exhausting on one cylinder bank, nothing is happening in the other bank, so connecting both pipes effectively enlarges the exhaust system, allowing these exhaust pulses to exit through both sides of the system. Exhaust flow is increased because both cylinder banks make use of both sides of the exhaust system, and increased exhaust flow equals more power.