Glad to see my merciless ranting has started some discussions
Killrob wrote:de-clutter and then add detail or vice versa, add detail and then de-clutter
Do you have any specific examples? That is not a very specific statement.
Ok now I see how bad I was at phrasing that statement

Here, I just made a screenshot of the engine designer to explain this best I can...

First thing you can do, is to close the info box (top left) by default, rather than open it by default. This already clears up a big part of the screen. Another option would be to make the info box a pop-up overlayed window, should the player click on "Info" or some icon. That would also allow the small arrow to be deleted forever from the left side there (you see for my picky bastard eyes, every little detail counts).
Second, the same applies to the limitations/specifications box (top right), maybe leave the arrow there for opening it and also the "visual" slider.
Third, the expanded menu at the bottom often gets me so confused and this is the place I spend most of the time wondering what the hell did I leave unselected... So to make it more compact and take up less of the screen, you could actually put it to the left of the screen and make it an expandable drop down menu, just turn the sliders sideways and make the whole menu scrollable with the mouse wheel. To prove the point here, the selection areas that you have for each component (ie the lists like "pushrod, overhead cam etc" for Head & valves is rarely "full", so it's the sliders that are using up most of menu height at the bottom and wasting screen area.
Little things, like the "Current Year" at the top of the screen could be an option somewhere inside the menu, rather than a separate element dominating at the top there.
This all allows for the semi-transparent bar showing component specs to move way low, right against the "step bar" at the bottom. And by the way, love the new step bar!!! Do not even sneeze on it

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Ok so I visualised all this in this image here (sorry for the lousy photoshopping, it's just to illustrate this post. And I also apologize for the Exhaust Diameter which is 6.00'', I know... promise it will never happen again.)

EDIT: Reading over my post, I realized this is pretty much the design geek inside me complaining about a design they didn't create themselves. So again, I want to be clear that I'm in no way trying to offend anyone, despite seemingly expressing myself in a rude way. If I didn't respect all the work that you have done, and hadn't fallen for the game, I wouldn't be here posting suggestions from my free time, so I hope everything is still cool.