BMW N55

The BMW N55 is a turbocharged straight-six petrol (gasoline) engine that began production in 2009. The N55 replaced the BMW N54 engine and was introduced in the F07 5 Series Gran Turismo.

The N55 was BMW's first straight-six engine to use a twin-scroll turbocharger. It also won three straight Ward's 10 Best Engines awards in 2011–2013.^[1]

Following the introduction of the BMW B58 engine in 2015, the N55 began to be phased out.^[2]

The BMW S55 engine is a high performance version of the N55 made by BMW M GmbH, which is used by the F80 M3, F82 M4 and F87 M2 Competition/CS.

The main differences between the N55 and its N54 predecessor are the use of a single turbocharger, the addition of Valvetronic and the type of fuel injectors. Whilst the N54 used a twin-turbo arrangement, the newer N55 uses only a single twin scroll turbocharger.^[3][4]Valvetronic (variable valve lift)^[5] is claimed to improve throttle response, low-rev torque, exhaust emissions and to reduce fuel consumption by 15%.^[6][5][7] The direct injection system uses solenoid-type injectors, instead of the piezo-type fuel injectors used by its N54 predecessor. The piezo injectors were more expensive and BMW decided they were not worthwhile outside of Europe, because the potential benefits of lean-burn operation could not be fully realised.^[5]

The exhaust manifold design, called Cylinder-bank Comprehensive Manifold (CCM) by BMW, aims to reduce the pressure fluctuations to reduce throttle lag and exhaust back-pressure.^[8] The twin-scroll turbocharger uses 2 sets of exhaust duct to turn 1 turbine wheel, with cylinders 1–3 and 4–6.^[9] The engine management system is Bosch MEVD 17.2, and compatible fuels are ROZ (RON) 91–98 octane (minimum RON 95 is recommended),^[10][11]

La relación de compresión es de 10,2:1, el diámetro del cilindro es de 84,0 mm (3,31 pulgadas) , la carrera es de 89,6 mm (3,53 pulgadas) y la cilindrada es de 2979 cc (181,8 pulgadas cúbicas ) , todo lo cual permanece sin cambios con respecto a su predecesor, el N54.       

El motor S55 es el motor de alto rendimiento desarrollado a partir del N55 por BMW M. Se introdujo en los M3 F80 y M4 F82, reemplazando al motor V8 atmosférico BMW S65 utilizado en la generación anterior del M3, y posteriormente se utilizó en el M2 Competition/CS F87 .

Las diferencias con respecto al N55 incluyen un bloque motor de cubierta cerrada, cigüeñal ligero, cojinetes de cigüeñal diferentes, pistones/bielas reforzados, muelles/material de válvula diferentes, turbos dobles, bombas de combustible dobles, escape activo, sistema de refrigeración revisado e intercoolers. ^{[ 18 ] [ 19 ]}

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