"real engine" refers to an actual or functioning engine, rather than a fake or imaginary one. It means something that is genuine and can truly be used to power a vehicle or machine. Full definition
This is real engine as one can get comparatively. (autoguide.com)
But the company's real engine of growth is in the fledgling wholesale and design side of the business — something that never would have happened had White not been paying attention to his customers» needs. (canadianbusiness.com)
A compression release brake (also known as a Jacobs brake or «jake brake»), is the type of brake most commonly confused with real engine braking; it is used mainly in large diesel trucks and works by opening the exhaust valves at the top of the compression stroke, so the large amount of energy stored in that compressed air is not returned to the crankshaft, but is released into the atmosphere. (en.wikipedia.org)