HKS releases a new exhaust joint pipe that goes in the middle of primary and secondary catalytic converter.
Stock φ54 pipe is a bottleneck even in the factory exhaust system. HKS pipe size is increased up to φ60 that greatly improves exhaust efficiency and goes great with bolt on turbo kit.
Stock φ54 pipe was purposely dented in several places for preventing interference with other vehicle parts (see photo). On the other hand, HKS joint pipe is φ60 and it was made in a layout without these dents. Due to the bigger bend radius than stock, the exhaust pressure is reduced and the power is increased.