Thermal efficiency is the paramount concern at Mercedes. That’s the measure of how much of the heat produced by the engine is converted into meaningful power for the car, and the company says its latest PU surpasses 45 percent. Having been at 29 percent in 2013, Mercedes has made a bigger advancement in the past few years than in the previous century and change — following the first internal combustion engines, which had a 17 percent thermal efficiency in the 1870s.
The Verge had a pretty interesting article on Mercedes F1 engine development a while back. The increases in thermal efficiency for the power unit over the last few years are flat out mind boggling.