bank engine can therefore be reduced and as the air fuel ratio detected at the location of the three way catalyst varies within a suitable range of tolerance the exhaust cleaning performance of the three way catalyst is improved application_number US 3388893 A description referring to fig1 of the drawings two banks engine blocks 2 and 3 each comprising a plurality of cylinders are disposed in a v type engine in symmetrical positions with respect to each other an intake pipe 4 is divided into intake manifolds 4a 4b downstream of a throttle valve 5 the intake manifolds 4a and 4b are respectively connected to various cylinders arranged in the banks 2 and 3 air is taken into the engine via an air filter not shown and supplied to each cylinder of the banks 2 and 3 via the intake pipe 4 intake manifold 4a and intake manifold 4b fuel is injected into the air by an injector 6 provided in the intake port of each cylinder exhaust gas manifolds 7a 7b are also connected to the banks 2 and 3 the manifolds 7a 7b combine together downstream in an exhaust gas pipe 7 a main catalyst 8 consisting of a three way catalyst is provided downstream of.