Ever increasing oil prices and emissions legislation have forced automobile manufacturers to investigate new methods and technologies to reduce fuel consumption in Spark Ignition (SI) engines. Two such technologies are Controlled Auto Ignition (CAI) and Cylinder Deactivation (CDA), both of which have the potential to decrease fuel consumption at light load. This paper presents synergies between running engines in CAI and CDA operation. A baseline simulation model of a production intent vehicle incorporating a four-cylinder engine was produced and correlated to measured test data. Experimental results of various CAI and CDA investigations have been projected onto the baseline simulation model and an analysis performed over the New European Drive Cycle (NEDC). It has been found that running an engine in CAI or CDA mode improves efficiency in explicit areas of the fuel map. These two modes of operation are complementary, allowing the potential to significantly improve fuel consumption over a broadened area of the fuel map. Mechanical valvetrain and exhaust system technologies, which enable both CAI and CDA to be employed concurrently on an engine using substantially standard components, are presented. Copyright © 2005 SAE International.