Alpina BMW B5
In the end, the key isn’t absolute horsepower, but the manner in which this performance unfolds. In this point, the youngest member of the ALPINA family takes a position at the head of the class – just as its predecessors in ALPINA history. The legendary B10 Bi-Turbo, for example, is a car that enjoys cult status today.
In principle, the B5 uses the same powerplant found in the familiar BMW ALPINA B7, with its eight cylinders and 4.4-litre displacement. The engine’s forced induction differs from conventional solutions: it is neither turbo, nor of the type of super-chargers that drain a great deal of power from an engine, especially at higher rpm.
A radial or ”Nautilus-type” compressor delivers the ALPINA V8’s boost pressure: one might see it as a combination of super-charger and turbo-charger. It isn’t propelled by exhaust gases, as a turbo would be, but rather belt-driven from the crankshaft. The inner workings of the radial compressor compare to the intake side of a turbo: a small turbine generates up to 0.8 atmospheres of boost to the cylinders. Before reaching the engine, the air passes through a generously-dimensioned inter-cooler, capable of sinking intake air temperature up to 70°C.
The advantages of this innovative technical solution? The radial compressor never stops spinning, with no time lag when power is demanded. Under the types of low to partial loads found in everyday driving, the engine operates as if it were normally aspirated, using the full functionality of Valvetronic (variable valve lift). This is the deciding factor in creating advantageous fuel economy. The compressor is controlled through the use of an ”upstream” throttle plate in the intake system – a development unique to ALPINA, and one that makes the charging of the Valvetronic V8, without the use of a common throttle body, even possible.
When looking at the horsepower curve, it’s clear what one may expect from this engine-bay-filling, complex technology. At a modest 2,500rpm one has 200 horsepower with which to play. At 5,500 rpm the maximum 500 horsepower are reached, but the fun doesn’t stop there: the engine maintains 500 horsepower up to maximum revs of 6,000rpm. A very wide power band, therefore, across which the B5 provides immediate, optimum power.
The torque curve is even more impressive. The curve takes on the form of a massive table mountain. At a mere 1,000rpm, just above idle, the V8 puts out 300 Newton meters of torque. Between 4,250rpm and 5,250, there’s a constant 700 Newton meters of twist on tap.
The engine characteristics, as evidenced by the above numbers, are those a of far larger, naturally-aspirated engine. The B5’s powerplant distinguishes itself by instantaneous reactions to throttle inputs, care-free revving up to maximum revs, and a nearly inexhaustible supply of acceleration across the rev range. At fullsong, the BMW ALPINA B5 needs but 4.7 seconds to reach 100km/h (Touring: 4.8 seconds), placing it in the fine company of the world’s most renowned sports cars.
Source: Alpina press