Intake system for multi-cylinder internal combustion engine

An intake system for an internal combustion engine having two rows of cylinders, each said row of cylinders being arranged not to fire one after another, and characterized by a valve overlap period wherein time required for an intake valve to open before a cylinder reaches a top dead center is set longer that time required to close after said cylinder has reached said top dead center, said intake system comprising:

• an intake manifold comprising a common intake passage, a collector intake passage for each said row of cylinders connected in common to said common intake passage and separate intake passages, each said separate intake passage branching off from one of said collector intake passages and being connected to an intake port of one of said cylinders of said internal combustion engine;
• an upstream throttle valve disposed in said intake manifold upstream of said separate intake passages;
• a downstream throttle valve disposed in each said separate intake passage;
• and
• control means for controlling said upstream and downstream throttle valves to throttle intake air into said cylinders by said downstream throttle valves in a light engine load range and by said upstream throttle valve in a heavier engine load range.