This paper provides an introduction to the technical challenges and countermeasures required to enable extreme gasoline engine downsizing. Jaguar Land Rover (JLR) is the lead partner in a collaborative project called 'ULTRABOOST' which is supported with funding from the UK Technology Strategy Board (TSB). The project aim is to develop an innovative engine concept capable of a 35% CO2 tailpipe reduction over the NEDC drive cycle relative to a current production V8 engine in a Sports Utility Vehicle, whilst maintaining key vehicle attributes such as performance and transient response. The project consortium is made up of eight technical partners including Jaguar Land Rover, Lotus Engineering, Shell Fuels, GE Precision Engineering, CD-adapco, University of Bath, University of Leeds and Imperial College London. Starting in September 2010 and running for three years the project will utilise the partners expertise and collective skills in engineering, design, combustion modelling, pressure charging and fuels to develop a highly pressure charged downsized engine concept. In this paper the technology required to enable extreme levels of engine downsizing and CO2 reductions are described, together with accompanying simulation data collected from the initial concept engine development. © Jaguar Cars Limited, 2011.