Here are the options:
* 2004 Audi A6 2.0T: This model came with a 2.0-liter turbocharged four-cylinder engine that produced 168 horsepower.
* 2004 Audi A6 3.0: This model came with a 3.0-liter V6 engine that produced 220 horsepower.
* 2004 Audi A6 4.2: This model came with a 4.2-liter V8 engine that produced 300 horsepower.
So, the base engine size for a 2004 Audi A6 can be either 2.0 liters, 3.0 liters, or 4.2 liters, depending on the specific trim level.
