In order to better understand how the Atkinson cycle and the Miller cycle influence the fuel consumption at different engine speeds and loads, an investigation was conducted to compare influences of early intake valve closing (EIVC) and late intake valve closing (LIVC) on the fuel consumption of a 1.5L turbo-charged gasoline direct injection (TGDI) engine. The engine was tested with three different intake cams, covering three intake durations: 251 degCA (the base engine), 196 degCA (the Miller engine), and 274 degCA (the Atkinson engine). Compression ratios are 9.5:1 for the base engine and 11.4:1 for the Atkinson and Miller engines, achieved with piston modifications. Results of this investigation will be reported in three papers focusing respectively on characteristics of the engine friction, in-cylinder charge motions for different intake events, and combustion and fuel economy without and with EGR for the naturally aspirated mode and boost mode. The present paper is Part I of this investigation. This study reports the results of detailed analyses as well as experiments on characteristics of the cam dynamics and friction forces for the three different intake cams at engine speeds from 700 to 5700 rpm. It was found that, for the three engines investigated in this study, the maximum motoring friction torque for the Atkinson engine was about 3% greater and the Miller engine was about 3% less than that of the base engine. Differences in the engine friction torques decreased with increasing the engine speed, and became insignificant at 5700rpm.