One thing quickly becomes apparent when looking at the Alpina B4. This is a car with a very different way of going about things than a BMW M4. Take the engine. Adding another turbocharger to the 435i's straight six might mean that both M4 and B4 are powered by twin-turbo 3.0-litre sixes but power delivery is very different. While the M4 pips the Alpina on power, its 425bhp figure comparing to 406bhp, the B4 comprehensively turns the tables when it comes to torque. With more than 600Nm of torque on tap, the B4 batters the M4's 550Nm.
Power goes to the rear wheels via a ZF eight-speed automatic 'box but this is no flabby slusher. It's so good and so responsive in 'manual' mode that you wonder why BMW ever went to the time and expense to engineer a twin-clutch for the M4. Thus equipped, the Alpina coupe will get to 62mph in just 4.2 seconds (4.5 for the Convertible). We're denied the left-hand drive 4WD versions, which is a shame as they're even quicker. If anything, the B4 rides a little more firmly than the M4, although that could be down to the huge alloys. A more accommodating sidewall profile will pay dividend on British roads. The optional £1,890 limited-slip differential is a must if you want to perform tyre-cremating drifts.
The Alpina B4 brings its own look, especially to the front end. The chin spoiler is a hefty appendage that would have Bruce Forsyth feeling a little under-endowed. There's also a four outlet exhaust with an acoustic valve, those hefty 20" alloy wheels in the company's famous multispoke design and every car gets a model plaque displayed on the centre console, showing the unique build number.
The interior gets luxury carpet overmats and subtle Alpina logos on the seat backs and door sills. The instruments are in Alpina Blue and the steering wheel is covered in hand-stitched Lavalina leather. Pay the extra for the B4 Convertible and you get an acoustically-insulated metal folding hard top that can be closed in just 20 seconds at up to 11mph.
Prices aren't that different to those of the M4, the B4 Coupe being pitched at around £59,000, while the Convertible wears a price tag of around £63,000. So, in coupe form at least, you're getting a car that's around £200 cheaper, just as rapid as makes no difference and a whole lot rarer. That's a formula that holds quite a bit of appeal.
Standard equipment also includes Adaptive M Sport Suspension, leather upholstery, electrically adjustable heated sports seats, climate control and Bi-Xenon headlights. In addition to being available with all BMW options including those from BMW Individual, the B4 Bi-Turbo can receive almost limitless personalisation from Alpina. Choices include hand-stitched full leather interiors and a wide range of hand-finished woods for the dashboard and doors.
We already knew the BMW 435i achieved some genuinely brain-bending fuel economy figures. The automatic car could notch 38.2mpg and emitted just 172g/km of carbon dioxide; amazing figures for a petrol-powered car that developed better than 300bhp. But do you know what? The Alpina B4s figures are, if anything, even more impressive. This is no simple bolt-on turbocharger installation. Alpina's engineers have gone to great lengths to tune and strengthen many of the engine internals too, fitting a forged crank and fettling the cooling system.
The result is that despite adding another 100bhp of muscle, the Alpina suffers only a tiny fuel economy penalty, the B4 recording combined cycle fuel economy of 37mpg and CO2 emissions of just 177g/km. The car's rarity value should prop up residual figures ahead of the M4, although insurance, consumables and servicing aren't going to be cheap.
It's easy to dismiss Alpina as a company that doesn't actually break much new ground; that piggybacks on the success of BMW's M division to a certain extent. That might have been true in the past, but in recent years, Alpina has developed a stable of cars that are brilliantly conceived, supremely engineered and come with a look and feel all of their own. There's actually very little crossover between BMW M and Alpina customers and the old image of fat businessmen choosing Alpinas has been changed with a series of cars that put a real emphasis on chassis dynamics rather than just straight line speed.
The Alpina B4 does it all. Here's a car that can hit 188mph, or 300km/h in new money, and yet it still gets better fuel economy than some hot hatches. It's beautifully finished and there's a genuine bespoke nature to the way you specify your Alpina that's way beyond that offered by mainstream manufacturers. If you want a car that never fails to feel limited-run special but is backed up by big-budget R&D, there's little to touch the Alpina B4.