Cadillac SRX chief engineer Liz Pilibosian challenged her team to achieve at least 300 horsepower while maintaining fuel efficiency in the 2012 model. “They came back and exceeded the goal with 308 horsepower,” she says.
Among other changes, GM engineers redesigned the car’s air induction and exhaust systems to get more horsepower and torque across a broader range of engine speeds. Those improvements help give the SRX the most standard power in its crossover segment, according to GM.
A car engine is basically an air pump, notes Robert Monchamp, lead calibrator for the GM team that designed the 3.6L SRX V-6 engine. “Air is directly proportional to torque and power is the time derivative of torque, so the more air we can pump through at any given time, the more power we can extract from the engine.”
“We wanted to continue our evolution of the SRX by improving the power and acceleration response of the vehicle,” adds lead development engineer Steve Kline. “By increasing air intake capacity, cooler and denser air is available to the engine, making it more powerful and responsive – especially on hot days in slow city traffic.”
The exhaust system improvements are extensive. “It’s all-new from the engine to the exhaust outlets,” Kline says. “From larger diameter pipes to a higher-volume muffler, the system is tuned to pull exhaust gases out of the engine at 1,200 to 3,000 RPM. This means more torque when you need it most.”
“Using hardware modifications alone, typically the choices are to tune for high horsepower at the expense of low-end torque, or to optimize for low-end torque with less horsepower,” says Monchamp. “But with the use of modern engine controls, we can tune the engine’s ignition and valve timing by moving intake and exhaust cam phasers, thereby changing the engine’s breathing characteristics, as often as every 3 milliseconds.” A magnetic sensor provides feedback on all four cam phaser positions twice per engine revolution, or as fast as every 4 milliseconds.
GM used Gamma Technologies’ GT-Power engine simulation/modeling tool in the SRX project early in the development phase to shorten lead time and minimize cost.