Despite the 50 years that lie between them, these two BMW race engines – the M121 (from the 2002 Ti race car) and P48 (that powers the 2019 M4 DTM) – have a number of similarities: both are turbocharged, inline-four cylinder 2.0-litre engines, both require a heat shield from the heat emitted by the turbocharger, and both use a mechanical fuel injection pump to supply the engine with fuel.
But that's where the similarities end.
With 50 years of technological advancement between them, the P48 pushes upwards of over 600 bhp (at 9,500 rpm) in race trim, from just two litres of displacement, and the whole engine weighs just 85 kgs.
Also, compared to the BMW M121 engine, the P48 engine outputs more than twice as much power, with far less consumption, and has a much longer service life. Note too, that the new four-cylinder ‘Class 1’ engines output approximately 100 bhp more than the V8 predecessors they replaced.
The M121 was the company’s first turbocharged racing engine, which, in 1969, earned BMW the European Touring Car Championship with Dieter Quester at the wheel. The pioneering four-cylinder engine produced approximately 280 hp at 6,500 rpm with 0.98 bar of turbo pressure. While the turbine could generate up to 1.76 bar of pressure – BMW’s engineers at the time concluded that the pressure in the cylinders would have been so great that the cylinder head would have just flown off!
Fast forward 50 years, and the P48 engine is able to manage up to 2.5 bar of turbo pressure thanks to specialised sand-casting procedures for the aluminium crankcase and cylinder head at BMW’s Landshut plant.
Components like the ignition distributor, fan, wet oil-sump, and boost valve have all since disappeared from the P48’s engine. The distributor and fan have been replaced by advanced electrical components, while a dry-sump oil lubrication system now circulates engine oil; the M121 had a direct charge air pipe (which meant compressed air could not be cooled before entering the engine), the P48 instead has a compact system to cool intake air.
Auxiliary units, like the starter and generator, are no longer on the engine but are mounted on the transaxle gearbox behind the engine, and a carbon fibre reinforced plastic intake plenum is now in place of a cast-and-weld metal unit. Even the throttle rod – which used a mechanical linkage system to open/close the individual throttle bodies – is now electrically actuated.
However, even the P48 race engine uses a high-pressure direct-injection fuel system similar to road-going BMWs, which is critical to the engine’s overall efficiency.
The BMW P48 engine will make its debut in the BMW M4 DTM when the 2019 season kicks off at the Hockenheim Circuit in early-May. Seven teams will do battle over nine rounds across Europe. BMW’s arch rival Mercedes-Benz has left the series to concentrate on its Formula E campaign, but competition will remain fierce from Audi (and its RS5 DTM racers) and for the first time, Aston Martin.