Atkinson cycle realized with a late intake valve closing (LIVC) and Miller cycle achieved with an early intake valve closing (EIVC) have been recognized as effective approaches for improving the gasoline engine fuel economy. In both Atkinson and Miller cycles, the engine can be designed with a higher geometric compression ratio for increasing the expansion work and the effective compression ratio is governed by the intake valve close (IVC) timing for the knock control. Duration of the intake event and IVC timing affect not only the pumping loss during the gas exchange, but also have strong influences on the friction torques of the intake cams and the turbulence intensities for the in-cylinder charge motion. The latter governs duration of combustion and EGR tolerance, both of which have impacts on the engine thermal efficiency. In order to better understand how Atkinson cycle and Miller cycle influence the engine fuel consumptions at different engine speeds and loads, an experimental investigation was conducted to compare influences of EIVC and LIVC on the fuel consumption of a 1.5L turbo-charged gasoline direction injection (TGDI) engine. The engine was tested with three different intake cams, covering durations of the intake event IDR = 251 degCA (base engine), 196 degCA (Miller engine), and 274 degCA (Atkinson engine). Compression ratios are 11,5:1 for the Atkinson engine and Miller engine and 9.5:1 for the base engine, achieved with piston modifications. The 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 study. It reports the results of detailed analyses as well as experiments on the characteristics of the cam dynamics and friction for the three different intake cams at engine speeds from 700 rpm to 5700 rpm. It was found that 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. The differences in the engine friction torques decrease with increase in the engine speed, and become insignificant at 5700rpm.