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This paper describes an investigation of emissions from an engine featuring variable valve timing, a swirlcontrol valve and exhaust gas recirculation. Design of experiments has been used to model the response of hydrocarbons and other emissions to the engine operating variables. The experiments identified the potential of VVT for simultaneous NOx, and HC reduction. The type of experiment employed was the Central Composite Rotatable Design; this is a fractional factorial design that maximises the amount of information obtained from a minimal number of test runs. A Fast Response Flame Ionisation Detector has been used to clarify the reasons for the effect of inlet and exhaust VVT on hydrocarbons.