The objective of this experimental study is to clarify the air flow rate characteristics of an MPI gasoline engine intake-manifold at transient conditions. A new high-response air flow meter was investigated and developed for the study which can simultaneously measure the air flow rate of all four cylinders. The influence of transient conditions to air flow rate distribution to each cylinder were researched and verified with regard to the geometry of the ram pipe length and location, and intake air pipe location for the air distributor. The transient conditions were examined by varying the following: initial throttle opening, throttle operating opening, throttle operating period, and engine speed and crank angle at starting to open the throttle valve. A comparison was also made with a “Siamese” type manifold.The air flow rate characteristics at transients were shown by using the relative rising ratio η (=Qi-QO)/QO, where Qi, QO are respectively the air flow rate of the i-th and the initial induction stroke)(1). We also proposed a new criterion method for transient air flow characteristics in this study. From the results of these experiments it is shown that (1)the “Siamese” manifold type has superior air flow response at the initial time of the transient compared to the MPI manifold type, but the MPI manifold is better at the latter half of the transient period, (2)the ram pipe length influence varies with the air flow characteristics at transient, and there is one most suitable length for transient conditions, (3)the air intake direction of the air distributor has a large effect on the air flow characteristics, (4)The transient characteristics for each cylinder were clarified in detail.