BMW M12 Engine History
The BMW M12 is a 4-cylinder, 16v engine, based on the BMW M10. Where the M10 used a timing chain, the M12’s camshafts and crankshaft were geared together. The M12 also utilised a dry sump lubrication system. Designed by Paul Rosche, it was produced in various capacities in both normally aspirated and turbocharged forms.
BMW M12/7 Engine
In 1972, in order to keep pace with Formula 1, the regulations for Formula 2 were changed to allow the use of 2000cc, production-based engines. At the time, the only engine available was the Ford BDG.
In the 12 months that followed, BMW created 50 M12/7 engines. Fitted with Bosch/Kugelfischer mechanical fuel injection, the 1991cc engine had an 89mm bore, 80mm stroke and compression ratio as high as 13:1. It produced in excess of 300bhp over 9000RPM. BMW struck an exclusivity deal with March to take all 50 engines that had been produced.
In 1973, the BMW M12/7 powered March 732 took to the track. In its maiden outing at the season opener at Mallory Park, piloted by the relatively unknown French driver Jean-Pierre Jarier, it won. Jarier would go on to win a further 7 races that season…and the championship.
Between 1973 and 1984, BMW M12/7 powered cars would go on to win 6 Formula 2 championships in total, making it the most successful engine of the 2000cc F2 era.
In 1977 and with just 12 weeks of development, BMW replaced its Group 5, 3.0L CSL touring car with an all-new car based on the E21 320 saloon. The short development time of the car was due, in no small part, to the already available and highly successful M12/7 engine.
BMW M12/13 Engine
In 1977, BMW struggled against the might of turbocharged Porsches in America’s IMSA series and contracted McLaren North American to build a 500bhp, turbocharged version of the M12/7 for use in the BMW 320, maintaining the same 2.0 litre capacity. In Europe, BMW also began to develop a turbocharged version of the engine for Group 5 racing. However, the engine capacity limit was 2000cc and in order to attempt to equalise the performance differential between naturally aspirated and forced induction engines, a capacity multiplier was used. For Group 5, the multiplier was 1.4, meaning turbocharged engines could only be a maximum of 1428cc.
Meanwhile, in Formula 1, Renault campaigned the first turbocharged Formula 1 car, the RS01. Initially not very successful, they continued to develop and refine it. By 1981, the venerable DFV was still dominating but Renault were becoming increasingly more successful. For the 1982 season, Ferrari, Alfa Romeo, Hart and BMW had decided to campaign turbocharged cars with various engine configuration.
Whilst others were using V6 and V8 turbo engines, BMW, using their experiences in Group 5 and IMSA racing, decided the way to go was a turbocharged version of the 4-cylinder M12/7, the M12/13. As with Group 5 racing, there was an engine capacity limit and a capacity multiplier for forced induction engines. For Formula 1 at this time, the capacity limit was 3000cc and the multiplier was 2, restricting turbocharged engines to a maximum of 1500cc.
The 1499cc M12/13 engine had an 89.2mm bore, 60mm stroke and 7.5:1 compression ratio. The engines used Bosch electronic fuel injection. In race trim, the 11,500RPM engines produced between 740-900bhp. In qualifying trim, however, up to 5.5bar (80psi) of boost was used to produce in excess 1280bhp! BMW themselves were not sure quite how much the engines were producing because, as Paul Rosche admitted, “It must have been 1,400 bhp, but we don’t know the exact figure since the engine dynamometer didn’t go beyond 1,280 bhp”.
To this day, the M12/13 remains the most powerful Formula 1 engine ever produced.
Cylinder Block “Seasoning”
Racing folklore has it that M12/13 cylinder blocks were hand picked from production M10-powered cars that had covered over 100,000KM. The theory being that any issues that could arise from manufacturing defects in the casting process would have shown themselves by that point. The folklore then takes a stranger twist; supposedly, BMW engineers would then leave these blocks outside, subjected to the elements for months at a time and then urinate on them for good measure! Paul Rosche apparantly described these blocks as “well-hung meat”. There is evidence to suggest that urine can have a sort of nitriding effect on ferrous metals. Indeed, swordsmiths of old would often quench their swords in urine – so it may not be as far fetched as it sounds. Either that or someone at BMW was just taking the p…
Ridgeway have decades of combined experience in building and rebuilding BMW M12 engines, ensuring they are just as dominant now as they were in period. We can also supply the components required to refresh or rebuild these engines.