Worlds most effiicient internal combustion engine.

[DaS Energy]

By doing away with metal pistons and other parts including the crankshaft efficiency vastly increases, and even further so as the combustion force not only drives the piston down it turns round and drives it back up again.

http://i1225.photobucket.com/albums/ee397/DaSEnergy/DaSEngine_zps466b9b7d.png

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[manuelgalvezferri]

So far I'd say its the Mercedes-Benz OM617 5 cylinder engine that came in either 2.5L and 3.0L turbo diesel forms, there have been taxi's with these engines in and have touched over 600,000 miles 966,000km, but apparently they have hit well over 1 million km. So my two cents goes to Mercedes Benz.