Engine size has gotten a revamp, and needs a bit tweaking. And is comprised in 2 parts.
One is just whether the physicality of the block and head choice fits. This allows us to use a simple look up table of engine sizes vs engine bays. Without having the combinatorial explosion of worrying about intake/turbo/exhaust choices. This is what the size arrows relate to. This also means the AI for the Tycoon game won’t have to cheat. The engines that it makes we can test fitment without having to load the 3D assets for.
Your other choices then increase the engines fill factor. We basically are saying, your Engineers will make this fit, just the more you fill the engine bay with large options, the more they have to work to squeeze it in. When an Engine is Turbo’d, it really eats up that fill factor, with finding room for the intercooler, piping, possible oil coolers. More powerful setups eating up volume faster. This is to try and make the Engineering/Design choices closer to real life, in a way we really can’t represent with 3D models.