2016 BMW M4 GTS
BMW has announced that the new limited edition BMW M4 GTS will be available for the first time in the United States. Only 700 examples of the high performance vehicle will be produced, 300 of which will make it to our shores.
The GTS has already lapped the Nurburgring in a very good time of just 7 minutes 28 seconds. Those who can get their hands on one are sure to be happy with the twin-turbo charged rocket.
The M4 GTS offers an output of 493 horsepower which is 16 percent more power than the normal M4. Peak torque is at 442 lb.-ft. and that represents a 10 percent increase over the non-GTS model. All of this power helps the BMW to launch from 0-60 mph in just 3.7 seconds and flat out it can hit 189 mph.
In producing this extra power and torque the M4 GTS remains as fuel efficient as the standard M4. Helping to get the power to the ground is a 7-speed dual clutch transmission.
The big technological advance in the vehicle is the water injection system. A first on a production road car. The system works by injecting a fine spray of water into the intake manifold where it evaporates. This results in lower air temperatures which is more dense allowing for more power to be created.
Innovative water injection system.
The BMW M4 GTS is the first production road car to be fitted with a trailblazing water injection system. With this arrangement, the BMW M engineers have utilized the principle that water absorbs heat from the surrounding air when it changes phases. Water is injected as a fine spray into the intake manifold plenum chamber where it evaporates (phase change), significantly lowering the temperature of the intake air. This action reduces the final compression temperature in the combustion chamber, minimizes the risk of knock and allows the turbocharged engine to operate with higher boost pressure and advanced spark timing. The result is increased power and torque, and a substantial improvement in efficiency. Despite the extra power output, thermal stress on all performance-related components is reduced. All of these features ultimately help to diminish wear and prolong engine life.
Increased power, reduced full-throttle fuel consumption.
The benefits of water injection can be utilized in various ways, depending on engine and vehicle type. In particular the engineers have considerable latitude when deciding how to balance their priorities between increased power and fuel efficiency. If water injection is taken into account in the design of a high-performance engine right from the start, it is possible to use turbochargers with a higher boost ratio and compression ratio. At the same time, power losses due to an increase in ambient temperature (> 68° F) can be compensated by increasing the amount of water injected.
The engineering behind intake temperature.
The output of an internal combustion engine is physically limited by the operating temperature in the combustion chamber. If a given operating temperature is exceeded, this will result in uncontrolled combustion (knock), leading to power losses and, in the worst case, to severe engine damage. This is particularly relevant in the case of turbocharged engines, where the intake air is heated in the turbocharger compressor to as much as 320° F. Although intercooling can be used to cool the pressurized air, the capacity of intercooling systems is physically limited. Depending on the design and size of the system, and the aerodynamics of the vehicle, it is only possible to use an intercooler to reduce the intake air temperature by as much as 160° F before it enters the plenum chamber. This means that simply rising engine power by increasing boost pressure is not an option as it would mean exceeding the knock threshold.
This is where the BMW M division’s solution comes in: if water is injected in a fine spray mist into the intake plenum chamber, it is possible to reduce the temperature of the intake air by an additional 80° F. This further cooling of the pressurized air makes it possible to advance the spark timing closer to the optimal value. This results in a more efficient combustion process, while at the same time reducing the final combustion temperature. An additional advantage is the fact that cool air is more dense which increases the amount of oxygen in the combustion mixture and results in a higher mean combustion pressure, leading to optimized power and torque development. This efficient in-cylinder cooling system also reduces the thermal stress on a broad range of components including not only the pistons, exhaust valves and catalytic converter but also, due to the lower exhaust gas temperatures, the turbocharger.
Water injection raises the knock threshold.
Using water injection to raise the knock threshold also goes a long way towards resolving a fundamental conflict in the design of high-performance engines, caused by the fact that power output and fuel consumption are closely dependent on compression ratio. This is particularly true in the case of highly turbocharged engines like the M TwinPower Turbo 6-cylinder in-line engine. Here, a high compression ratio provides high efficiency and low fuel consumption at low and medium throttle. In the full-throttle range, however, the compression ratio is limited by the knock threshold. Water injection provides a particularly effective way of raising the knock threshold, allowing for a higher compression ratio. The end result is optimized power output over a wide operating range.
Clever practical implementation of the water injection system.
The BMW M division’s engineers opted for an arrangement of three water injectors in the intake plenum chamber where each supply water to two of the straight-6 engine’s cylinders. This solution makes for uniform water distribution and a compact system design.
An underfloor compartment in the trunk houses a 1.3 gallon water tank, the water pump, sensors and valves. The pump and all the sensors and actuators are controlled by an expanded engine management system. The pump supplies water to the injectors at a pressure of approximately 145 psi. The injection quantity can be varied depending on load, engine speed and temperature, which helps to keep water consumption to a minimum. Under hard driving on the track, the water tank might have to be topped up every time the vehicle is refueled. However under normal everyday operating conditions, the intervals are much longer. Even in highway driving, the water tank only needs topping up at every fifth refueling interval. Otherwise the system is maintenance-free, for maximum everyday practicality.
The BMW M water injection system is equipped with a sophisticated self-diagnosis system. If the water tank runs dry, or in the event of a system malfunction, appropriate measures are taken to protect the engine. Boost pressure and spark timing are adjusted, allowing the engine to continue to operate safely. Even when things are working normally, a variety of precautions are taken to keep the system fully functional. Every time the engine is switched off, all the water in the hose system is drained into the tank to prevent system components from icing up in sub-zero temperatures. The water tank is frost-proof.
“Special Edition models sharpen the character of the BMW M brand and embody an emotionally rich and exclusive driving experience. We’ve taken a radical route with the set-up of the BMW M4 GTS to create a sports machine for the race track that delivers top-end dynamics and inspirational performance. It allows us to demonstrate what is possible today with a road-legal car. Owners can drive their BMW M4 GTS to circuits such as Spa-Francorchamps, the Nürburgring or Laguna Seca – for clubsport events, for example – and then set lap times there that raise the bar to extremely high levels for road-legal cars.” said Frank van Meel, CEO of BMW M GmbH.