Tomei Expreme Unequal Length Exhaust Manifold/HeadersHigh Efficiency 4 1 Type We introduced the high efficiency 4 1 as against the STD 4 2 1. The exhaust efficency of the standard exhaust manifold is not perfect. But Tomei 4 1 type exhaust manifold has high efficency. You could see the change of dramatically driving feeling. Not Equal Length Design The complete equal length is good for the exhaust intervention but reduce the turbine performance and increase the exhaust resistance. Contrary to that, the