The best way to fully understand what happens inside of an engine is to take one apart and then put it back together. You'll get your hands on the smallest of pieces that work together with the larger ones to turn air and fuel into horsepower and torque. Of course, it's not quite that simple for most people to pull an engine out of a car and then rip into it to discover its secrets. That's why a 3D-printed scale engine might make for a great educational tool.
A YouTube user by the name of Eric Harrell created just such an engine in what appears to be 1/4 scale. It's a GM LS3 V-8. There are plenty of other 3D-printed engines out there, but this one is pretty darn wonderful in all of its LS detail. The creator utilized a number of CAD files and also turned to images and other bits of data found online. The result of those ones and zeroes sent to the 3D printer is this rotating and whirring scaled-down engine.
Those who have the equipment and are interested in printing up their own versions of this engine can find the files on Thingiverse. Mr. Harrell will also sell printed up engines or various parts.
This LS3 is essentially the modern version of the classic Visible V-8 from Revell. That classic model kit is still produced to this day, but it's an older engine and it's not like you created it yourself with your own 3D printer. Get your hands on either scale engine, though, build it up, and you'll learn a lot about how cars work.