Power of three: new engines from BMW

This engine heralds the dawn of a new era as BMW enters the world of three cylinders.

Michael Seitz
Miguel Perez

Efficiency and dynamics: for many years now, BMW vehicles have offered drivers both. And it’s all thanks to the BMW EfficientDynamics strategy, of which engines are a central pillar. No other manufacturer develops new engines so frequently and invests so much in the process. In 2014, an all-new family of engines is writing the next chapter in this story – indeed, for many observers, it marks the beginning of a whole new book. For the first time in its history, BMW is fitting three-cylinder gas and diesel engines in its cars. The standard unit serves as the entry point into the line with output of 102 hp.

The position of the pistons reflects the uniform ignition sequence of the three-cylinder unit. Inside the cylinder head, BMW Valvetronic controls the inflow of air.

The new three-cylinder’s light weight places less of a load on the front axle, making for increased agility and steering pleasure.

At the same time, it demonstrates its impressive potential to deliver high-performance propulsion even in the hitherto unfamiliar environment of the BMW i8. The engine develops a full 231 hp in the hybrid sports car, while its 154 hp per liter of displacement outperforms all other BMW series-produced engines. The engine developers in Munich (gasoline) and Steyr, Austria (diesel) are also moving the game forward in terms of fuel consumption. The new power plants burn 5-10 percent less fuel than a similarly powerful four-cylinder engine from a rival manufacturer, depending on the car and output. The key feature here, alongside the lower cylinder count, is the far-reaching BMW EfficientDynamics tech package. All the new three-cylinder engines use BMW TwinPower Turbo technology. In the gasoline variants, this includes direct injection, turbocharging and Valvetronic fully variable valve control. Each individual element performs a specific role in enhancing efficiency and dynamics. The direct injection system feeds minuscule amounts of fuel into the cylinder in fractions of a second and ensures it burns efficiently, while a special turbocharger generates high output and enviable torque even at low revs.

The exhaust gas flows through the turbine wheel (left) and turns it. This causes the compressor wheel (right) to rotate as well and push fresh air to the cylinder, boosting output and torque.

The exhaust gas flows through the turbine wheel (left) and turns it. This causes the compressor wheel (right) to rotate as well and push fresh air to the cylinder, boosting output and torque.

The driver can therefore move up through the gears early, spend a lot more time in higher gears – and save fuel as a result. A three-cylinder construction also lends itself to the additional boost provided by a turbine in the exhaust gas flow. The air generated by the three cylinders flows quickly and evenly to the turbine’s vanes. These begin to rotate rapidly and push fresh air to each cylinder. The faster the turbo spools up, the more direct the communication between the engine and the accelerator. The new engine sees BMW using a water-cooled manifold to cool the engine’s exhaust gases – one of the first manufacturers to do so. The exhaust produced by the turbocharged gas engine reaches an extreme 1,800°F, but the new system allows BMW engineers to make it run more effectively. Further increases in efficiency are achieved immediately in front of the combustion chambers in the cylinder head, where BMW Valvetronic ensures a low-loss supply of air. In addition to these technical details, the three-cylinder engine also has some other clear advantages. Its light weight places less of a load on the front axle, which makes for increased agility and steering pleasure. The engine is also smaller, leaving more space in the engine compartment for future drive system solutions, such as hybrids. All in all, the new engine displays a brand of performance and lack of vibrations that are more reminiscent of six cylinders than four – much less three! That means effortless acceleration up to 6,500 rpm and a sonorous burble feeding off the same frequencies as a six-cylinder unit. This provides BMW acoustic engineers with excellent raw ingredients for some alluring sound effects. Indeed, drivers of the new three-cylinder models will have little need the radio during the early miles: hearing the engine for the first time is like listening to a trio singing in triple time.

New engine strategy

This three-cylinder is the trailblazer for a new generation of BMW gas and diesel engines. Forthcoming four- and six-cylinder variants will also adopt its cylinder capacity, technical make-up and design features. It marks its debut in the BMW i8 hybrid sports car.