The main change between the Alpina B4 and the 435i, apart from the obvious cosmetic tweaks, is to the 3.0-litre turbocharged inline six-cylinder engine under the bonnet.
With an additional turbocharger, new cooling system and a forged steel crankshaft, the B4 BiTurbo produces a meaty 300kW of power and 600Nm of torque, 75kW and 200Nm up on the car on which it's based.
0-100km/h takes an M4-rivalling 4.2 seconds (4.5 seconds for the convertible), on its way to a top speed of 303km/h (301km/h convertible) - which puts the B4 BiTurbo in supercar territory.
Fuel consumption is rated at 7.6L/100km and 8.0L/100km combined for the coupe and convertible respectively. Drive is sent to the rear wheels via an eight-speed automatic transmission.
Starting at $160,900 plus on-road costs for the coupe, the B4 BiTurbo comes equipped with adaptive LED headlights, adaptive cruise control, adaptive Alpina suspension, electrically-adjustable heated front sports seats, head-up display, 'Merino' leather upholstery and BMW's ConnectedDrive online infotainment system.
Distinguishing the B4 from the 'regular' 435i on the outside is a unique body kit, Akrapovic exhaust with quad tips and 20-inch Alpina alloy wheels.
Despite the healthy list of standard equipment, like most BMWs, the Alpina B4 is available with a number of options, including a hand-stitched full-leather interior and an array of interior trims for the dashboard and doors.
There are 12 special exterior colours to choose from, including the signature Alpina Blue and Alpina Green, in addition to the range of paints offered from BMW, commanding between $1600 and $8100.
Other cost options include a heated steering wheel ($358), an electric rear sunblind ($641) and a TV tuner for the infotainment system ($1866).
The B3 sedan will kick off from $155,900 plus on-road costs, while the more practical Touring starts at $160,900 before on roads.
Stay tuned to CarAdvice for more Alpina updates.