HKS Equal Length Header - Scion FR-S / Subaru BRZ 2013+The HKS exhaust manifold was designed in the same 4-2-1 type layout as stock but with better flow and performance...
The HKS exhaust manifold was designed in the same 4-2-1 type layout as stock but with better flow and performance for lower engine RPM torque. Because the first catalytic converter is mounted at the exhaust manifold, the exhaust creates a pulsatory motion that makes the exhaust gas pull back into the pipe at middle RPM range which causes a loss of output by behaving as an exhaust gas recirculation system. HKS still follows the same design exhaust manifold layout 4-2-1 but by making it without the catalytic converter HKS eliminates the gas draw back creating both more torque at middle RPM range and more peak power at high RPM. You can easily feel the smoother acceleration through the lower RPM band into the high RPM band with smooth transition.
