As Alcibiade says, the Engine Designer example script included with FMOD Studio is just that: An example. Specifically, it’s an example of how you could mirror a game’s code for handling engine parameters in FMOD Studio for the purposes of auditioning.
It does not represent the best or only way to model an engine. Every game has different requirements, and so every game models its engines differently. Racing games, for example, tend to have complex engine events with many parameters representing different components of the engine’s behavior, because engines are so important to that genre; whereas a game that only features engine noise as part of its background ambiance might not control its engine with parameters at all.
As with any event, you should decide what you require an engine event to do in your game, give the event the content required to produce that behavior and the parameters required to control that content, and write code for your game that sets those parameters to the appropriate values at the appropriate times.