Multi-cylinder spark ignition engine

A multi-cylinder spark ignition engine having four or more cylinders into which a fuel containing at least gasoline is injected,

• the multi-cylinder spark ignition engine having a geometric compression ratio of higher than 12, and comprising:
• an exhaust manifold connected to respective exhaust ports of individual cylinders;
• a variable exhaust valve timing mechanism for changing a valve opening time of an exhaust valve;
• an ignition timing controller for controlling an ignition timing of a spark plug provided in each cylinder;
• and
• an effective compression ratio adjuster for adjusting an effective compression ratio,
• the exhaust manifold having a plurality of branched exhaust passages connected to the respective exhaust ports of the individual cylinders;
• a plurality of first collector segments each of which joins the branched exhaust passages for the cylinders which are not adjacent in the exhaust order sequence;
• a plurality of middle exhaust passages connected to the downstream of the first collector segments, respectively;
• and a second collector segment that joins the middle exhaust passages,
• in at least low and middle speed ranges in a high load region of the engine, an effective compression ratio being adjusted to have a value larger than 10 by the effective compression ratio adjuster, the ignition timing being retarded by a predetermined amount from the MBT by the ignition timing controller, and the valve opening time of the exhaust valve being changed according to the engine speed by the variable exhaust valve timing mechanism so that a predetermined amount of a valve overlap period of an intake valve and the exhaust valve is ensured in a case where the valve opening time and a valve closing time of the intake and exhaust valves are defined with the valve lift of 0.3 mm, and that the negative pressure waves from the exhaust pressure pulses reach an exhaust port of a cylinder during the valve overlap period of that cylinder in a plurality of engine speed ranges.