BMW has secretly created E34 M5 and Z3 Roadster convertibles with V12 engines
To mark the 50th anniversary of its M division, BMW has been showing off once-secret prototypes in a series of videos, and the two featured in the latest video released Wednesday are among the most unusual to date. Back in the day, BMW built prototypes of the E34 M5 convertible and Z3 M roadster, both powered by V12 engines. Both cars are now part of the BMW Museum's M 50th anniversary exhibit.
It is unclear why BMW M built a convertible version of a four-door sedan, but it was a thorough job. Since there were no roof pillars to mount the seat belts, engineers relocated them to the seats themselves. They also designed a mechanism on the top of the car body to provide trunk room.
The E34 M5 was powered by a 3.8-liter inline 6-cylinder engine that transmitted 340 hp and 295 lb-ft of torque to the rear wheels via a 6-speed manual transmission. It is fascinating to experience this powertrain in the open air, and this is not the only oddball E34 built by BMW's Skunk Works, which also installed a 6.1-liter V12 engine for the McLaren F1 in its E34 M5 wagon.
By comparison, the V12 Z3 M roadster looks almost orthodox. The prototype was first unveiled in 2012 and is powered by what appears to be an M73 engine. This 5.4-liter V-12 engine was used in the 7 Series when the Z3 was in production. Maximum output is 321 hp, far exceeding the 240 hp of the stock M roadster.
It was surprisingly easy to fit the V-12 into the Z3's engine compartment. Although the car itself is small, the engine is almost the same length as the inline 6-cylinder of the stock M roadster. The only difference is that it has two banks of cylinders instead of one; the V-12's heavier weight seems to have had an effect on the car's weight distribution.
The video also briefly shows a 1991 BMW M8 prototype that is part of the same museum exhibit: based on the E31 8 Series, it is a more powerful version of the same generation S70 6.0-liter V-12 engine with 550 hp, however, However, BMW decided against commercializing the car, and the prototype was put in storage. It was recently restored to running condition by BMW.
The BMW M experiment did not end there. The engine from the Le Mans-winning V12 LMR racing car was mounted in an X5 to create an SUV that could lap the Nürburgring in under eight minutes.
More recently, BMW also experimented with CSL versions of the M3, M5, M6, and M2. None of them went into production, but BMW recently brought back the CSL badge on the M4.
