RUF is one of the select few automotive institutions in the world that can take a Porsche, tear it apart, tweak it, glue it back together, and the result is a better car than the stock vehicle. The Pfaffenhausen-based company’s lineup saw no shortage of extreme builds over time, but few can surpass the RUF BTR.

Offered for only six years (between 1983 and 1989), the RUF BTR was named after Group B, as BTR stands for Group B Turbo RUF.

Name aside, the BTR is also an exceedingly rare bird. RM Sotheby’s says only 20 to 30 units were ever built, but RUF also offered customer conversions which were hard to track. Usually, the BTR would be developed using a 911 930 Turbo or a Carrera 3.2 as donor vehicle and the amount of work RUF put into each BTR was nothing short of gargantuan.

First off, the engine’s displacement would be bumped up to 3.4 liters. Then RUF would tweak the turbocharger, add a twin-plug ignition setup and voila, 374 horsepower. Mated to the engine was RUF’s in-house-developed five-speed manual gearbox which allowed for a 0-60 mph sprint time of just 4.3 seconds and top speeds of around 190 mph.

Other visual and creature comforts goodies included the RUF-branded instrument cluster, Recaro seats with race-grade harnesses as well as RUF-made 17-inch alloy wheels and a new steering wheel.

The car that’s going under the hammer during RM Sotheby’s Detroit event on April 21-29 started life as 1981 911 930 Turbo. The conversion was performed in 1987, when the owner sent the car over to RUF, who fitted the dog-leg five-speed manual, an oil cooler hidden inside the redesigned front fascia, and a speedometer calibrated for mph. Since then, the car spent all its time in California before being acquired by a private collector of sports cars from Michigan. He also repainted the BTR.

The car is expected to fetch between $90,000 and $110,000.