(1.500cc turbo, with ERS and KERS)
The powers to be in Formula 1 (specially FIA president, Jean Todt) decided it was time to show a more ecological-friendly image to F-1. It wouldn’t be the case of talking only about a Formula One engine, but power units. These power units use extra power converted from the brakes and turbo, via electrical motors. No more limits on when to use all the available horsepower. Trouble is that turbo-compressed power was out of the circus since the end of the eighties. New power-plants proved too complicated to develop and make reliable. Unreliability plagued the very first test and it was hard to integrate all systems. The rules limited fuel consumption with a maximum of 100 kg/hour. It demanded more efficiency to keep (or make better) the numbers of the aspirated V8s. To control budgets, the number of engines available per year is also limited. One can go ahead of the total, but being penalized with grid positions loss.
To make matters worst, initially FIA decided for the use of a token systems. To prevent huge costs, each unit is developed with respect to a points scale. Problem is that, who started the new formula badly had little room to improve. Those with a better project would shine, just as Mercedes did. Their engine had unique features like the compressor and the turbo on the extremes of the block, rather than together. They also had a better weight (and components) distribution.
Teams and manufacturers are coy about real numbers. But the belief is that actual power units deliver up to 650hp (combustion engine). Some 250 extra hp coming from the DRS. But the fastest lap times established with the old generation engines prevailed until 2016, when finally the new power units could deliver all its strength.