Before BMW produced the M535i or introduced the original M5, its Motorsport division was already transforming E12 5 Series sedans into high-performance machines. One of the rarest examples, a 1979 conversion with a 3.5-liter engine, will be auctioned in Austria in October 2026.

The first-generation 5 Series arrived in 1972, the same year BMW established its Motorsport department. By 1974, the small M team was taking cars from BMW’s Dingolfing production line and reworking them in its own facility.

These early conversions were not always easy to identify or order through a conventional BMW dealer. Cars that began as 525, 528, or fuel-injected 528i models could receive larger six-cylinder engines sourced from BMW’s CS coupe, 6 Series, and E3 sedan.

An early M performance formula

The most powerful version of the early program was the 533i, fitted with a 3.2-liter inline-six producing 197 horsepower. Its stated top speed of 132 mph placed it in the same performance territory as a base Porsche 911 of the period.

The upgrades extended beyond engine swaps. Available equipment included a five-speed manual transmission with a dogleg first gear and direct-drive top gear, a limited-slip differential, sport dampers, and alloy wheels with wider tires.

Owners could keep the cars relatively discreet or emphasize their Motorsport origins with bold graphics and spoilers. The car heading to auction takes the more conspicuous approach.

A 3.5-liter E12 built before the M535i

Built in the summer of 1979, the Polaris Silver sedan began life as a carbureted 525. Its original 2.5-liter M30 engine was replaced by a 3.5-liter unit from the 635CSi, raising output to 218 horsepower and the stated top speed to 138 mph.

The conversion also includes wide 14-inch BBS Mahle wheels and Auto Sport Spezialsitze bucket seats. The combination of engine, chassis, and interior changes made the car an early expression of the formula BMW would later apply to the production E12 M535i, which arrived in 1980.

The car is now with its fourth owner and has been fully restored. Its rarity is difficult to quantify, although only small numbers of these Motorsport conversions are believed to have been built.

October 2026 auction

Humer Granner will offer the E12 in Austria on October 17, 2026. The car will be sold without a reserve, with an estimated value of €75,000 to €95,000, equivalent to approximately $84,000 to $106,000.

As an early BMW Motorsport conversion produced before the M535i and original M5, the sedan represents a little-known chapter in the development of BMW’s M road cars.