In a previous paper [ 1 ], the authors have proposed a cost effective air hybrid concept based on a proprietary intake system and cam profile switching (CPS) system [ 2 ]. It was shown through engine simulations that the pneumatic hybrid operation could be achieved with about 15% regenerative efficiency. The proposed air hybrid operation can be achieved with proven technologies and engine components and hence it represents a cost-effective, reliable and quick deployable solution for low carbon vehicles. In this work, a four-cylinder 2 litre diesel engine has been modelled to operate on refined air hybrid engine configurations and the braking and motoring performance of each configuration have been studied.Both air hybrid systems can be constructed with production technologies and incur minimum changes to the existing engine design. The regenerative engine braking and staring capability is realised through the employment of innovative proprietary intake system and production cam profile switching (CPS) devices. The 1st hybrid engine configuration is shown to be capable of producing compressed air to 15 bar during its compression mode operation. Both hybrid systems will allow the engine to be cranked by the compressed air at moderate pressure without using an additional starter or dedicated valves in the cylinder head. Therefore, the proposed air hybrid engine systems can be considered as a very cost-effective regenerative hybrid powertrain and can be implemented in vehicles using existing production technologies.