The 2979cc straight-six cylinder engine with high-precision direct injection, Valvetronic and Bi-Turbo charging delivers 410hp (301kW) between 5500rpm and 6250rpm and a maximum torque of 600Nm at only 3000rpm. In fact 550Nm are available across an impressively wide range between 2200rpm and 5200rpm. Mated to the excellent ZF 8-Speed Sport-Automatic transmission means that the new Alpina BMW B3 Bi-Turbo and B4 Bi-Turbo models are never lacking in forward momentum - power can be called upon at all times in order to enjoy that typical, effortless Alpina driving experience.
The new B4 Bi-Turbo Coupé accelerates from 0 to 100km/h (0 - 62mph) in just 4.2 seconds, passing the 200km/h mark in 14 seconds on the way to a top speed of 305km/h. At the same time the powertrain, which features Valvetronic and Start Stop, boasts class leading economy figures with a combined consumption of only 7.6 litres per 100 kilometers and CO2 emissions of just 177g/km.
The prerequisite for these impressive values is a high-tech engine which exhibits its own unique characteristics thanks to a significant number of stand-alone features. With the aim of achieving excellent responsiveness, high output across the entire rpm range and an improvement in fuel consumption, a Bi-Turbo engine configuration was required. This type of turbocharging has the benefit of providing very good response and pick-up due to the low mass moment inertia of the turbocharger's running gear and sufficient rate of air-flow for spontaneous power delivery.
The design and construction of the excellent BMW 3.0 litre straight-six cylinder (N55) engine serves as a starting-point for a specially cast aluminium block with Bi-Turbo capable flanges. These enable the mounting of two turbochargers along with required oil and water connections and a close-coupled catalytic converter arrangement. Alpina specific NGK spark plugs and a forged steel high-strength crankshaft guarantee long-lasting stability.
Always-on power delivery and excellent throttle response are aided by an electronically controlled bypass valve system. Specially constructed and de-throttled, i.e. flow and cross-section optimised, air intake ducts guide the air with minimal losses from the air intake via the air filter housing to the turbochargers. On the fuel side, a high-performance high-pressure fuel pump ensures the right throughput. Optimal utilisation of the output is provided by a high-capacity intercooler with flow-optimised collector boxes made from aluminium. Coolant cooler, additional separate coolant and engine oil coolers as well as a high-performance cooling fan ensure the thermal stability of the cooling system in all conditions.
Inspired by the pleasure that the 8-Speed Sport-Automatic transmission with SWITCH-TRONIC offers in the larger BMW Alpina models, the so-called 8HP70 transmission has been extensively adapted to suit the performance characteristics of the new B3 and B4 Bi-Turbo models.
In actual fact, the high power output and torque of the Bi-Turbo combine so well with this transmission that performance figures usually associated with much larger but less efficient engines are achieved.
Furthermore, this transmission excels in disciplines often assumed to be incompatible and offers an optimum driving experience in every situation. To this end, three shift modes are available: Automatic (D), Sport (S) and Manual (M).
In Automatic (D) Shift Mode the focus is strictly on driving comfort. The transmission changes gears quickly and with no noticeable interruption to the delivery of power. The torque of the engine enables consumption-optimised 'surfing' in high gears even at very low speeds and in urban driving environments. Even at higher cruising speeds rpms will remain low, for example 2500rpm at 170km/h in 8th gear, increasing long-distance driving comfort significantly.
Sport (S) Shift Mode noticeably shortens the time it takes for the next gear to engage and depending on engine load significantly moves the shift points up the rev range. Accelerator inputs are carried out immediately, full throttle i.e. kick-down will implement multi-simultaneous downshifts and optimal acceleration. When combined with the Sport or Sport+ setting of the Drive Performance Control, which modifies the drive and chassis setup, gearshifts are even quicker.
Activating the Manual (M) Shift Mode using the SWITCH-TRONIC buttons on the back of the steering wheel, allows the driver to take control and shift gears when suitable or necessary. A special feature of the Sport, Sport+ and DSC Off setting is the suppression of automatic up-shift in Manual (M) Shift Mode - hereby the selected gear is held into the rpm limiter and the transmission will not up-shift into a higher gear.
Abundant torque allows the use of a long rear axle ratio which in combination with the 8-Speed Sport Automatic transmission and Auto Start Stop contributes significantly to achieving excellent fuel economy. Top speed is achieved in 7th gear. Additional hardware modifications for dealing with output and torque include reinforced front and rear axle differentials, high-strength output and drive shafts and a high-torque transmission gear unit.
The stainless steel exhaust system which was developed in collaboration with Akrapovic is 7.5kg lighter in comparison to its predecessor. The resonant, sporty sound of the exhaust system is controlled by an intelligent exhaust valve. This offers the driver the possibility to influence the sound experience via the Drive Performance Control and facilitates the balancing act between emotional soundtrack and long-distance comfort. In Comfort mode the exhaust valve remains closed up to 2500 rpm, beyond which it opens depending on engine load and rpm. In Sport mode, however, the valve is permanently open and the B3 Bi-Turbo thrills with its distinctive aural character under hard acceleration - when additionally selecting Sport (S) or Manual (M) Shift Mode the exhaust will deliver an occasional burble on the overrun.
Urejal _T_O_M_O_, 20.11.2013, 20:40.