Every O.S. helicopter engine undergoes rigorous testing to meet the demands of even the most aggressive pilots. Fly challenging maneuvers with extra confidence — select an O.S. heli engine with pressurized DRS (Demand Regulator System), and know that you'll always have consistent fuel flow regardless of your model's attitude. For optimum horsepower, look for the factory-tuned Speed engines with advanced timing. Most O.S. heli engines include: