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.
The complete equal length is good for the exhaust intervention but reduce the turbine performance and increase the exhaust resistance. Contrary to that, the not-equal length exhaust manifold can lead the efficiency of other cylinders. Tomei design the not-equal length.
