Recently further improvements of fuel economy and performance of truck diesel engines are required in the market. At the same time, countermeasures for exhaust emissions are requested as a clean air activity. So the improvement of performance and the reduction of emission are keysubjects today.As a countermeasure for both problems, the reduction of friction is effective. The authors took notice of the pumping loss, and analyzed the pumping loss at the gas exchange process and improved the performance by a multi valve intake & exhaust system. Particularly the multi valve system is effective on a higher boost and/or smaller sized engine because of its larger air and gas flow through the relatively small passage. And the reduction of the fuel rate resulted in better reliability with regard to thermal load and exhaust temperature.