Small Diesel Engines - Natural Aspiration vs Turbo Charged?

[Fallon]

It is a common saying that turbos are free power, but Its not actually free horsepower. However, it is a very efficient power adder. And there are drawbacks to turbos that aren’t there with a supercharger, ie turbo lag. Superchargers offer instant throttle response, but transmitting a hundred or more horsepower with a belt and pulleys wastes energy. Transmitting the energy with compressed air is more efficient ...if the piping is sized and bent correctly.
It’s just in most Diesel engines, instant throttle response is not a major concern. Efficiency and longevity are more important.

Compressed air is a lot less efficient at transmitting energy that a driveshaft or belt. It's just that the pistons have already extracted most of the energy they can from combustion.

 

[Agvg]

There's "free power" which a turbo recovers in the form of unused energy in the exhaust (definitely a few percent, though not a ton). Typically though turbos are used to make a small engine act like a bigger one... including most of the big engine's mpg...

If you talks about car engines a turbo makes the engine much more nice to use, the last that impressed me was a 130hp 1.2 gasoline engine, max torque 205Nm at 2000 rpm, and of course is far more efficient than a non turbo with the same output. Just the weight reduction is significant, and weight cost fuel.