What’s being described as an “onboard weather station,” the 3.6L twin-turbo LF3 V6 engine launching in the 2014 Cadillac XTS Vsport and 2014 CTS Vsport this fall is equipped with a set of sensors that monitor air pressure, intake humidity and throttle intake temperature. These monitors continuously send data to the engine’s wastegate and compressor bypass control system to make the most of engine efficiency and moderate temperature.
One of factors monitored by the sensors is compressor surge, which is an air flow reversal that can limit power output and increase unwanted noise. To minimize this, the sensors continually measure air pressure in the compressor, and optimize the wastegate position to produce maximum power and eliminate unwanted noise. The wastegate regulates the pressure at which exhaust gases pass to the turbine by opening or closing a vent to the exterior. Science.
Another element that needs to be put in check is something called “co-surge,” which is unique to twin-turbo engines. This happens when an air flow imbalance exists between competing compressors, leading one compressor to surge. Co-surge is most common in high altitudes, where low barometric pressure can more adversely affect vehicle performance. The engine corrects these air imbalances by re-positioning a pair of vacuum-actuated wastegates on each turbocharger. This process allows the exhaust to bypass the turbocharger’s turbine wheel and merge into the exhaust stream, optimizing turbine speed throughout the power band.
Air temperature is another issue that needs to be monitored. During hard driving, compressed air temperature can exceed 265 degrees Fahrenheit, which thins the air density entering the engine, and thus decreases power. However, Cadillac’s on-board weather station detects temperature conditions and a unique charge air cooling system reduces the temperature by more than 130 degrees, increasing the air density to provide maximum power and performance.
Lastly, the LF3’s humidity sensor keeps moisture in the air in check and modifies combustion spark and cam timing to make the most of engine efficiency and performance in multiple weather conditions, like rainy Seattle or the dryness of Las Vegas.