This latest test mule was spotted at BMW's Nurburgring test centre
This production-ready model sports only limited camouflage
A reveal at the Geneva motor show next year is expected
The B4 is likely to share its underpinnings with the B3 Biturbo
Changes to the front bumper are still being kept under wraps
Both the B4 and B6 have been spotted testing at the circuit
The car has been seen on track in recent weeks
Power will most likely come from a twin-turbo straight-six engine
Such a combination would give the B4 404bhp and 443lb ft
Before the B4, Alpina will reveal the B6 Gran Coupé at the Frankfurt motor show in September
The 532bhp twin-turbo 4.4-litre V8-powered model is not destined for sale in the UK
Alpina says that's because it will be built in left-hand drive guise only
The Alpina B6 we tested recently was fast and responsive
This Gran Coupé seems to be undergoing changes to its front and rear bumpers
The new Alpina B4 Biturbo has again been spotted at the Nurburgring.
This latest test model was seen parked outside BMW's test centre, which is based at the circuit.
The Alpina B4 Biturbo — Alpina's answer to the BMW 4-series — is likely to share its mechanical package with the new B3 Biturbo, with power coming from a twin-turbo straight-six engine with 404bhp and 443lb ft.
The B4 is tipped to be launched at the Geneva motor show in March before reaching the UK next summer.
Meanwhile, the B6 Gran Coupe has also been spotted testing, having been revealed at the Frankfurt motor show. However, this 532bhp twin-turbo 4.4-litre V8-powered model is not destined for sale in the UK because it will be built in left-hand drive only.
Autocar recently drove the new Alpina B6 Biturbo in regular coupé form, finding it to be a powerful and competent high-speed cruiser.