First BMW all-wheel drive was unveiled in 1985 as a second-generation BMW 3 Series. All-wheel drive was offered exclusively in conjunction with a 2.5-litre six-cylinder in-line petrol engine producing 171 horsepower. The permanent all-wheel drive of the BMW 325iX channelled power to the front and rear wheels at a constant 37 : 63 percent split. Visco locks in the transfer case and final drive took their cues from the difference in rotation speed between the front and rear wheels to provide virtually fixed connections if required, and in this way optimise traction and driving stability. From 1988 customers could also order a Touring variant of the BMW 325iX.