Engine Family Adaptions
In the tycoon mode, have the ability to create new engine families based on existing ones. So for example if you have a SOHC engine, you can start a new family of DOHC engines that are otherwise identical to the SOHC engine and save development costs over designing a new engine from scratch.
This system could also be used for changing block and head material and changing V8s from crossplane to flatplane. Another thing I would like to see is if you could adapt one engine type into another, for example the Triumph V8 was essentially 2 of their existing I4s joined to a common crankshaft.