ENGINE BMW N55

BMW’s new N55 engine family’s 306 horsepower and 400Nm power and torque output figures reminds us of the original moment when BMW first announced it was bringing back forced induction into the BMW engine line-up. The N54 engine was factory rated to put out that exact same amount, and it did that via the use of gasoline direct injection and two turbochargers running together, fed gas from three cylinders each.

Three years later, we still have 306 horsepower and 400Nm of torque, but BMW has achieved it using only one turbocharger instead of two. The new N55B30 engine also churns out peak boost and torque faster than the N54, with 400Nm hit at the 1,200rpm point instead of the N54B30′s 1,3000rpm mark

VALVETRONIC FOR BMW N55

BMW engineers probably finally managed to cram all that technology into the engine and make it possible for them to work all together. The new N55B30 has both a new generation Valvetronic variable valve management system and High Pressure Injection (direct injection at up to 200 bar). Valvetronic replaces the throttle butterfly functions with a control unit infinitely varying the valve stroke on the intake valves. This means the intake is not obstructed by a partially closed throttle during low load operations. The new N55 also features a map-controlled oil pump which takes up less energy, which BMW says is a first in a turbocharged engine.

One of the variations of the Volkswagen EA888 engine also features variable valve management combined with direct injection but the EA888′s valvelift system is only fitted on the exhaust valves of the engine and works in two stages – a high cam and a low cam, unlike Valvetronic which is continuously variable.

Fitted in the newly unveiled BMW 353GT, the new N55B30 engine takes the machine from 0 to 100km/h in just 6.3 seconds, up to a top speed of 250km/h.

irated direct injection engines also do not feature Valvetronic.

                                                             TWIN SCROLL

The single turbocharger uses twin scroll technology. The twin scroll turbine housing uses dual side by side exhaust gas inlets into the housing, fed by two sources of exhaust pulses. A single path is also not able to take advantage of all the exhaust gas pulses effectively. Since there are two passages, each has a smaller overall volume than a single scroll turbo path, thus the exhaust velocity of each pulse can be maintained.

The N55B30 is not the first BMW engine to use a twin scroll turbocharger, as the BMW Prince engine in the MINI Cooper S also uses one. In the Cooper S, the turbocharger’s twin-scroll principle is fed by two sets of two cylinders each, while in this N55 inline-6 engine it is two groups of 3 cylinders each.

The N54 did not feature valvetronic because in a turbocharged engine, throttle losses can be countered by the positive pressure of the turbocharged air being blown into the engine. But the main reason there was no Valvetronic is because the complexity of designing a cylinder head that could fit Valvetronic mechanisms as well as direct injection. It is because of this reason that the N53 normally asp 

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BENEFIT

•     N55 slightly better fuel economy. ( 1-2% but technically there is upto 5% due to twinscroll turbo)

        slightly better efficiency (5-7% according to the modified.com article)

        Combination of direct injection, turbo and valvetronic (actual benefit i am           unsure.

         However this is  the first time these have been used together so I am                   assuming there is some sort of synergistic affect)      

        Peak torque comes on 200rpm earlier at 1200.

         Engine is 9pounds lighter.

•     Peak torque doesnt really come on early as claimed, there are dynos to prove this. I dont know why BMW does this, but they are completely bullshitting us when they say the N54 makes maximum torque at 1500, more like 2200 and the N55 is about the same.

•     There isnt much difference stock for stock powerwise between the two engines. After tuning though, it 'seems' as though the N54 will just be the better platform. Dont forget that valvetronic is yet another variable thrown in the equation for tuners to try and play with. And believe  me, they will probably leave it locked out for simplicity and for maximum power if all else.

•     Twin scrolls are nice, but id rather have the 9 lbs heavier engine with the extra turbo.