The thunderously capable but impressively refined BMW M5 is with us, but anyone wanting a performance version of this generation 5 Series prior to the launch of BMW’s headline saloon would have had to turn to the Alpina B5 Biturbo.
Until recently, Alpinas have avoided using the same engines as M division products, but the B5 comes pretty close to going head to head with the new M5. It shares the same basic 4.4-litre V8 engine (the inlet set-up is different), equipped with two retuned turbochargers.
In Alpina tune, BMW’s twin-turbocharged 4.4-litre V8 produces 532bhp at 5200-6250rpm and 541lb ft from just 2800rpm. That's enough, says the firm, to take the car from 0-62mph in 4.5sec and onto a gloriously unrestricted 198mph.
The engine is fitted with an eight-speed automatic transmission which has been developed by Alpina and ZF and has a trick way of speeding up shifts when you select one of the car’s sportier modes
Instead of merely retarding the engine timing, the B5 uses its direct injection tech to switch off a cylinder. Alpina says the system cuts gearshift times in two, to around 180 milliseconds, thanks to the reduction in torque.
This version of the B5 also gets revisions to its suspension settings and the arrival of the tyres that the car was always designed to be fitted with: non-runflat Michelin Pilot Super Sports.
Unsurprisingly, the B5 is a jaw-droppingly fast car, and on the road Alpina’s own claimed 0-62mph time feels, if anything, conservative. The engine has massive urge from beneath 2000rpm, allied to a classy, deep, V8 exhaust burble; it’s refined, albeit not as characterful as the sound of AMG’s latest twin-turbo V8, but if you push on it makes a great Nascar-esque soundtrack.
There’s colossal torque on offer, but the B5 is perfectly docile for everyday use; cruise along a motorway at 80mph with the engine spinning at barely 1900rpm and it's silent.
That trick transmission works well and seems happy to cope with all that shove, too; select the most extreme mode and it holds on to gears to allow you to get involved with the steering wheel-mounted buttons (although we’d prefer a paddle option), and we can't think of many dual-clutch units that beat it on speed and smoothness.
But the truth is that making a 5 Series with this engine feel strong on a motorway was never going to be the biggest challenge faced by Alpina's engineers. More testing is the task of making it handle on poor surfaces and twisty roads, particularly of the sort we find here in the UK.