The principal engine used in passenger cars is, and in the foreseeable future will be, the SI Engine. This paper summarizes AVL's experience in developing SI Engines for these vehicles. Special attention is given to the new targets of SI Engine development and the resulting design strategies during the concept phase of new engine families. The new modular concept of engine families includes a broad range of different engine designs like three to five cylinder inline and six to ten cylinder V-block engines, direct injection or fully variable valve actuation. It is shown that the design of central engine components, for example, that of the cylinder head, can be adapted for the different SI valve-train concepts by simply switching specific modular components.This modular design approach for main engine components facilitates more flexible engine families and therefore significantly decreases the time to market, the costs of development and production of new variants of one engine family. A reduced time to market in combination with an exact definition of the engine specifications is one prerequisite not only to fulfill future customer and market requirements but also to observe varying emission laws with their different test procedures.