The B4’s engine is one of the finest in the business. It’s a BMW 3.0-litre six-cylinder petrol unit fitted with two turbochargers, which means when you push it hard, it’ll produce a ferocious 434bhp; ask it to pull from low revs and its stout torque means you rarely need to drop a gear in search of more go. It’s a brilliantly smooth engine, too, at any revs, and taking it close to its redline brings a wonderfully raucous straight-six noise from its sports exhaust.
An eight-speed automatic gearbox is standard and feels urgent on the move when left to its own devices or when asked to swap gears using the B4 S’s wheel-mounted button changers. However, at slower speeds in town, the B4 S’s throttle response can feel a little sharp and the gearbox can struggle to keep up when creeping through traffic, even in Comfort driving mode.
Talking of driving modes, the B4 S has Eco, Comfort, Sport and Sport Plus settings, which bring an increasing amount of focus to its drive. These include weightier steering, better throttle response and stiffer suspension in search of more involvement for the driver. But even in its sportier settings, the B4 S isn’t the same animal as a BMW M4.
It’s softer, for starters, and doesn’t feel quite as eager to scythe into bends, but on the UK’s appalling Tarmac, that can often be good thing. It still steers extremely well (better than an RS5 and C 63, for instance) and often feels more planted, especially in wet conditions. Being softer helps it feel less skittish, but also its standard limited-slip differential does a brilliant job of sending power where it’s needed for more effective cornering. And when the grip runs out at the B4 S’s rear wheels, it feels far less savage in the way that it snaps sideways versus an M4 in the same situation.
Also, when dialled back to Comfort mode, it’s far more comfortable than the rigid M4 on long journeys, despite wearing huge 20in Alpina-specific alloy wheels as standard.