Well, i played the demo, and i am planning make a preorder 
im happy with the game.
my suggestion is, the abbility to adjust the idle rpm, the idle on ‘real’ engines dont affect the final performance, but helps in autonomy and life time, u can think about it?
another one, when u are testing tha engine, after the game revs the engine and complete the ‘dyno’ u can freely rev ur engine to see if its working fine, and in add u can put some weight to the engine (on flywheel) and test how will rev.
ok an another is Boxer enignes are on plan? and Wankels? Radial (like aero engines)?, cause if is to make an game, u need to make the thing right
i will like if u put all kinds of engines, hit’n’miss, 2 stroke, electric, all types, so we can make some weird cars
thanks
sorry about my english, i’m brazilian