The Sierra 4-cylinder turbo refers to GMC's 2.7L TurboMax engine, a turbocharged four-cylinder that serves as the base engine for the Sierra 1500, delivering strong performance for its size. This engine produces around 310 horsepower and 420-430 lb-ft of torque, offering impressive towing and payload capabilities, competitive fuel efficiency, and features like Direct Injection, Active Fuel Management, and a strengthened block for enhanced durability and performance.