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Bodystyle, dimensions and technical details

To a large extent, visually at least, you know what you’re going to get with an Alpina: multi-spoke alloy wheels with threateningly low-profile rubber and subtle, often angular body additions.

A couple of our testers thought the styling a touch fussy around the front of the latest 3 Series and others – the majority – that it was right in keeping with Alpina’s heritage. Either way, those who know about Alpina will know this is an Alpina. Ditto with those 20-inch alloys, which are covered in, perhaps crucially, rubber that isn’t of the runflat variety.

Alpina doesn't tamper with BMW's classic formula, so the longways straight six is still up front, driving the rear wheels

The tyres are the most outwardly apparent elements of a thorough overhaul of the 3 Series’ dynamic make-up. The suspension is, of course, based on the latest F30-series 340i with adaptive dampers, but the B3 wears bespoke Eibach springs that are 45 percent stiffer and has its own bump stops and Alpina-specific anti-roll bars (albeit sourced from BMW).

There is more negative camber, while the front subframe, with a strut brace, has been redesigned, partly to increase body rigidity and partly by necessity, because the B3 gets a twin-turbocharged, rather than single-turbo, variant of BMW’s 335i engine that headed the range at launch.

Alpina says this is because its two smaller turbochargers take less time to spool than even BMW’s twin-scroll turbo. A twin-scroll inlet for a single turbocharger negates some of the lag associated with a large turbo, which is why BMW adopted it for its N55 six-cylinder engine. With such a turbocharger, incoming exhaust gases are separated into two scrolls (the curved pipes that circumnavigate the turbo housing and direct exhaust gases towards the turbine).

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On a straight six, each scroll takes its gas from three cylinders – those whose exhaust valve cycles don’t overlap – which in turn makes for more efficient spinning of the turbocharger. Typically, the scrolls pump gas at the turbine at different angles and pressures from each other (and even on to different parts of the turbine) — one scroll to provide quick response, the other for peak performance.

However, Alpina believes that two smaller turbochargers are quicker still to respond, hence it has junked the N55’s single, twin-scroll turbo and developed its own twin-turbo solution. This requires use of twin-turbo-capable flanges, which are already cast into the N55’s aluminium crankcase – handily leaving the door open for the return of two turbos on the upcoming BMW M3 and M4.

Alpina's tweaked engine also has a forged steel crankshaft, Alpina-specific ECU and wiring loom, NGK spark plugs, a high-performance fuel pump and a 40 percent bigger intercooler than that used on the BMW 335i.

The upshot of all these modifications is that the 3.0-litre straight six, which drives the rear wheels through a ZF eight-speed automatic transmission, produces 404bhp and 443lb ft – a particularly impressive result, especially when you consider that the claimed combined fuel economy is 37.2mpg.

Other notables include Alpina’s own tuning of BMW’s variable sport steering (which quickens off the straight-ahead; it’s not active steer) and stability programs, and an optional (but not fitted here) limited-slip diff. Brake discs are ventilated, not drilled, and 370mm in diameter at the front, 345mm at the rear.

The B3 Biturbo is also available in the more practical outfit of the 3 Series Touring, which gives a compelling mix of power and practicality in one dosage.