This paper describes the initial works related to the study of intake plenum which is a part of intake manifold. The effects of intake plenum length/volume on the performance characteristics of a spark-ignited engine with electronically controlled fuel injectors were investigated with the aim of constituting a base study to design a variable length intake manifold plenum. The results showed that the variation in the plenum length causes an improvement on the engine performance characteristics especially with the fuel consumption at high load and low engine speeds which are put forward the system using for urban roads. According to the test results, plenum length must be extended for low engine speeds and shortened as the engine speed increases.