The B3 S Bi-Turbo is the closest thing to a M3 Touring.

Storied BMW tuner Alpina has upgraded the B3 Bi-Turbo and the B4 Bi-Turbo in time for next week's Geneva Auto Show. The two models are based on the 3 Series and the 4 Series, respectively.

The bulk of the upgrades made to the S variants are found under the hood. The B3 and the B4 both use a turbocharged 3.0-liter straight-six engine rated at 440 horsepower and 486 pound-feet of torque. In comparison, the same engine generated 410 horses and 442 pound-feet in the outgoing models.

Buyers can choose either rear- or all-wheel drive, but transmission options haven't been revealed yet. In its fastest configuration, the B4 hits 60 mph from a stop in 3.9 seconds. It's about as fast as a M4 equipped with the optional Competition Package.

The B3 is available as a sedan and as a station wagon -- it's the closest thing to a M3 Touring on the market, at least for enthusiasts who live where Alpinas are distributed. The B4 is offered as a coupe and as a convertible. All variants receive discreet visual tweaks including new lights on both ends.

According to Motor 1, the Alpina B3 S Bi-Turbo and B4 S Bi-Turbo are on sale now in Germany -- Alpina's home market -- and in a handful of other nations including China and Australia. The 6 Series-based B6 is sold in the United States, but Alpina has no plans to sell the B3 and the B4 on our shores.

Both models will be displayed next week during the Geneva Auto Show. They'll share the spotlight with the brand new B5, which is based on the latest 5 Series.