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. The direct injection system uses solenoid-type injectors, instead of the piezo-type fuel injectors used by its N54 predecessor. Valvetronic (variable valve lift) is claimed to improve throttle response, low-rev torque, exhaust emissions and to reduce fuel consumption by 15%. Whilst the N54 used a twin-turbo arrangement, the newer N55 uses only a single twin scroll turbocharger. 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. īMW S55 engine is a high performance version of the N55, which is used by the F80 M3, F82 M4 and F87 M2 Competition/CS. įollowing the introduction of the BMW B58 engine in 2015, the N55 began to be phased out. It also won three straight Ward's 10 Best Engines awards in 2011–2013. The N55 was BMW's first straight-six engine to use a twin-scroll turbocharger. The N55 replaced the BMW N54 engine and was introduced in the F07 5 Series Gran Turismo. This is the first time I've heard of two-stage torque specs (or repeat-torque specs) for spark plugs or crush washers single-stage torques did just fine on my oilhead.The BMW N55 is a turbocharged straight-six petrol engine that began production in 2009. Theory: if relaxation is an issue (and I'm not saying it is), it could cause the integrity of the seal from a single-stage torquing to decrease over time.Īlternative theory: two-stage torque action gives time for oil to flow out of areas that are critical for sealing, allowing a more robust seal to be formed by the second stage/cycle of torque. Possible aluminum crush washers do so as well, but that'd be news to me. Plastics are famous for this, but the only metal I was aware of that exhibited C&R was lead. Relaxation: the tendency of a material to exhibit decreasing stress over time as a result of constant strain (distortion). Some materials exhibit a pair of related properties called 'creep' and 'relaxation.'Ĭreep: the tendency of a material to exhibit increasing strain (distortion) over time as a result of constant stress. Never the less, those are the specifications as I understand them. Time for the material to flow out a bit? Doesn't really seem reasonable in my mind. I understand that the oil drain plug uses a crush washer (also replace each use), but really don't know why you torque to one level, stop, and then proceed to another.

Bmw torque specs