prototype of this mid level model debuted at LeMans in 1981, an unusual strategy implemented by Porsche at the time. Called the 924 GTP LeMans, the car was based on the 924 Carrera GT LeMans that competed in the event prior to the GTP's introduction. The most noticeable change in the new race car was the departure from the Audi sourced 2.0 L inline-4 engine in favour of the 2.5 L engine developed by Porsche. The new engine was mounted at an angle of 45 degree to the right and utilised a dual overhead camshaft along with counter rotating balance shafts, an unusual and unique feature for its time that provided better weight distribution and ensured smooth power delivery by eliminating inherent vibrations resulting in the engine lasting longer. A single KKK turbocharger producing enabled the engine to generate a maximum power output of at 6,800 rpm. The engine also utilised Bosch's prototype Motronic engine management system to control ignition timing, fuel injection and boost pressure. The new race car proved to be much more fuel efficient than its predecessor, stopping only 21 times in 24 hours for fuel. The 924 GTP managed seventh position overall behind the race winning 936 and a class win at the GTP+ 3.0 category in 1981 before being retired and stored in the Porsche museum. In 1982, Porsche debuted the production road legal version of the race car, called the 944. The car utilised many technologies its race bred sibling had used, including the balance shafts and the engine management system, but power was toned down for safety purposes. The new all-alloy inline-four engine, with a bore of and stroke of , was in essence, half of the 928's 5.0 L V8 engine, although very few parts were actually interchangeable. Not typical in luxury sports cars, the four-cylinder engine was chosen for fuel efficiency and size, because it had to be fitted from below on the Neckarsulm production line. To overcome roughness caused by the unbalanced secondary forces that are typical of inline four-cylinder engines, Porsche included two counter-rotating balance shafts running at twice the engine speed. Invented in 1904 by British engineer Frederick Lanchester, and further developed and patented in 1975 by Mitsubishi Motors, balance shafts carry eccentric weights which produce inertial forces that balance out the unbalanced secondary forces, making a four-cylinder engine feel as smooth as a six-cylinder engine. Porsche spent