How does the design choices matter in the final game?

Very interested about this game but I have my doubts about it.
First of all I tried the Engine Designer Demo (just the inline 4's) and found out that it is actually fun designing new kinds of engines. But if the games ultimate idea is to build your own car company, then I would like to know how it is going to (gameplay wise) make any difference if your engine has 100hp or 120hp? How is the game considering the situation if you have high reving engine or low reving engine in your car(s). I mean there are just ton of choices and combinations you can make just in this engine designer! If you have adjustments then these adjustments should also have (at least) somekind of impact in the final game, if they don’t have any impact in the full final game, then gameplay wise when looking at the big picture, they are pretty much pointless adjusments.
Im not sure how many adjustments there are going to be the car body designer, but as far as I can see it, the same thing applies to that as well.
PS. I also think that designing new engine should be somewhat rare treat. It should cost so much (as it kind of does in the real world when you calculate all the manufacturing changes and stuff) that you just cant design new engine for every new model, at least not in the early days.
First of all I tried the Engine Designer Demo (just the inline 4's) and found out that it is actually fun designing new kinds of engines. But if the games ultimate idea is to build your own car company, then I would like to know how it is going to (gameplay wise) make any difference if your engine has 100hp or 120hp? How is the game considering the situation if you have high reving engine or low reving engine in your car(s). I mean there are just ton of choices and combinations you can make just in this engine designer! If you have adjustments then these adjustments should also have (at least) somekind of impact in the final game, if they don’t have any impact in the full final game, then gameplay wise when looking at the big picture, they are pretty much pointless adjusments.
Im not sure how many adjustments there are going to be the car body designer, but as far as I can see it, the same thing applies to that as well.
PS. I also think that designing new engine should be somewhat rare treat. It should cost so much (as it kind of does in the real world when you calculate all the manufacturing changes and stuff) that you just cant design new engine for every new model, at least not in the early days.