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Brabham-BMW BT52: Revision of the BMW M12 / 13 engine

General overhaul of the Brabham-BMW BT52
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E s was the smallest engine that ever created a formula 1 World Championship. And the strongest. The BMW M12 /13 had a displacement of just 1.5 liters and four cylinders. Calculations showed that it should have delivered up to 1,430 hp in qualifying laps with the wastegate valve removed.

At that time, the BMW Motorsport GmbH test benches could only run up to a maximum of 5.1 bar boost pressure. It read 1,065 hp. The cockpit display in the Brabham BT54 from 1985 ended at 5.5 bar. During training, the steam wheel was turned even further. So the maximum value could only be calculated.

It all started with BMW being successful with the M12 /7 four-cylinder in the 1970s. The basis of the engine comes from the BMW 1500 from 1961. The Bavarians also had experience with turbo engines from the German racing championship and the IMSA series.

After Renault converted its V6 Formula 2 engine into a 1, 5 liter turbo for Formula 1, the plan in Munich to try it a class higher also matured. The 1.4 liter turbo from the touring car already delivered 550 hp at 2.6 bar boost pressure and 10,500 rpm. More than the then widespread Cosworth V8 in the premier class.

Nelson Piquet, here at the 1983 race in Hockenheim, became world champion thanks to BMW power.

Formula 1 project in the second attempt

The BMW technicians led by Paul Rosche that you could start the Formula 1 adventure with at least 550 hp. The board of directors still had to say yes. And that was difficult enough. Race director Jochen Neerpasch had the plan to work with McLaren as aAlly team and Niki Lauda as drivers. Lauda resigned, the board said no, the project died.

But only temporarily. Neerpasch's successor Dieter Stappert had forged the plan together with Rosche to build the Formula 1 engine and use it first at Brabham and later on with other teams. Quasi as a Cosworth replacement for the turbo era. The Austrian finally convinced the skeptical gentlemen at BMW headquarters with the argument that Brabham boss Bernie Ecclestone was joining forces with the man who had the say in GP racing.

BMW appeared with his in 1981 supercharged four-cylinder for the first time in public. In training for the GP England. For now only for 14 rounds in training. The appearance of the 557 hp four-cylinder engine shocked the competition. Nelson Piquet would have been in fourth place with a time of 1:12.06 minutes.

A Brabham BT52 in individual parts. The car was completely overhauled at BMW.

Piquet wins 1983 world champion with BMW power

BMW put his supporters off until 1982. The first year was a touchstone for the Brabham-BMW marriage. There were problems with the ignition and injection control units. The best software had been destroyed by a power surge. It took forever to reproduce the desired map values.

Because success did not occur straight away, Ecclestone re-equipped a car with the Cosworth engine. After Nelson Piquet failed to qualify at the US GP in Detroit, they almost got divorced. BMW forced the use of a car with Piquet at the wheel for the following Canadian GP. The miracle happened. Piquet won just seven days after the bankruptcy of Detroit in Montreal in the Brabham-BMW ahead of Riccardo Patrese in the Brabham-Cosworth.

From then on, the four-cylinder turbo became a success story. Nelson Piquet won the world championship in Kyalami in 1983 with engine block number 58. The breakthrough came with a special fuel development by partner Wintershall in the second half of the season.

The team that built the now 680 hp miracle engine in Munich with Paul Rosche at the helm was exactly 41 employees. 1984the performance went through the roof with ever higher boost pressures. From 680 to 760 to almost 900 hp. At a certain point in time, the KKK turbochargers no longer played. The defending champion landed only two wins.

Brabham built his chances of success in 1985 with a Pirelli contract and in 1986 with an extremely flat car. BMW had to install its four-cylinder in the BT55 inclined 72 degrees to the left in a subframe. Only the 'upright' engine achieved a victory. In the Benetton B186 with Gerhard Berger at the GP Mexico. 1987 ended the first era of BMW in Formula 1.

After the revision, 610 HP were measured on the BMW test bench in regular operation.

Brabham BT52 has to go to a major inspection

The wonderful four-cylinder turbo is still there. Every now and then it is started with the Brabham BT52 for historical occasions. In 2019, however, the fans had to forego the sight of the legendary racer and the engine in the rear. The experts in the BMW Classic Department had ordered a general overhaul.

The engine overhaul was actually due after 600 kilometers. With reduced boost pressure, the mileage was then extended to 800 kilometers. After that, however, they no longer wanted to take the risk of greater damage. It was time to dismantle the engine and inspect it more closely.

But when dismantling the individual drive components, the mechanics were astonished to discover that the four-cylinder unit was still as healthy as possible. Only a few bearings were changed, the piston rings replaced and the cylinders honed a bit and resealed.

The biggest change concerned the turbocharger. The engineers decided to recently build a charger based on the Monaco configuration. It delivers a little less pressure and thus also a lower performance, but should be a little more stable. To be on the safe side, those responsible also decided to digitally record the exact dimensions of the turbocharger. In this way, the component can be reproduced true to the original in the event of damage.

Marc Surer reeled off the first kilometers with the completely overhauled racing car on the track at the BMW plant in Regensburg.

Marc Surer drives the shakedown

After the overhaul of the individual components, the engine was carefully run in on the BMW test bench. The performance was measured with approx. 610 hp. For comparison: in 1983 the engine still had 650 hp until the race in Hockenheim. The lower output is not only due to the changed turbocharger but also to a larger ignition angle to the knock limit of the engine.

Before the first public appearances, the Brabham BT52 also had to go to the mandatory shakedown on the run-in lane at the BMW plant in Regensburg. The former F1 driver Marc Surer was allowed to unwind the first kilometers with the completely reassembled racing car. Because of the cool temperatures, however, the car was placed on the dry asphalt with soft rain tires.

On the straight, Surer turned in sixth gear directly up to 10,500 rpm (shutdown speed). With the built-in gear ratio, this corresponds to a speed of 285.44 km /h. Even in fourth gear, the rear wheels lost their grip when accelerating, which was not only due to the power but also to the reduced tire grip. After the exit, Surer nevertheless drew a positive conclusion: 'The car drives very well. The performance is more than sufficient and can be dosed well.'

In the gallery we show you many fascinating pictures of the overhaul and the shakedown, garnished with further technical information on the individual components.

Technical data BMW M12 /13 engine:

  • Type: 4-cylinder row
  • Installation: lengthways
  • Displacement: 1,499 cm³
  • Turbocharger: 1 (Garrett, KKK)
  • Bore * stroke: 89.2 * 60.0 mm
  • Valves: 16, spring
  • Compression: 6.7: 1
  • Weight: 165 kg
  • Performance : 580-1,430 HP
  • Maximum speed: 9,500 /min - 11,500 /min
  • Control: spur gear set
  • Designer: Paul Rosche


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