Formula One cars currently use 1.6-liter four-stroke turbocharged 90-degree V6 double-overhead camshaft (DOHC) reciprocating engines. These engines are designed to a strict set of dimensions and material limitations, with the cylinders arranged in a V-shape. They were introduced in 2014 and have been developed over the subsequent seasons. The power a Formula One engine produces is generated by operating at a very high rotational speed, up to 20,000 revolutions per minute (rpm), although they are electronically limited to 15,000 as of the 2014 season. The engines are electronically controlled and use a hybrid system that consists of a petrol internal combustion engine and electric motors powered by an Energy Recovery System (ERS) . The ERS recovers energy from the cars braking system and exhaust gases, which is then stored in a battery and used to power the electric motors. The current F1 engine regulations dictate that each team must be powered by a four-stroke 1.6-liter V6 engine, which includes a turbocharger and an Energy Recovery System. The engines are highly efficient and powerful, producing over 1000 horsepower. The use of smaller cylinders in the engines allows for greater efficiency and reduced heat losses.