When I make a new engine for a car, after deciding on layout, I almost always have to chose the valvetrain first (second tab) before chosing the cylinder bore.
Otherwise the size arrow will turn red when I go to the second tab and decide, and I have to go back and reduce the bore.
Can you make it so that when the top end is empty, the game assumes that the length of the engine will be with the widest valvtrain (DOHC 5v i think), until you actually make the choice?