Originally Posted by TouringDan
We can all speculate on how well a vehicle will tow and the resultant fuel economy towing, but until we actually "tow with it" we really don't know. Glad that you will be getting some test data with a normal Taurus and a turbo 2.0L Escape.
You seem to be suggesting that turbo gassers may suffer more loss of fuel economy towing than turbo diesels. If testing bears this out, then that is ok; it is what it is. However, I don't understand why the turbo gassers should suffer a larger percentage loss of fuel economy towing than turbo diesels.
Normal turbocharged gasoline engines run a VERY different cycle than turbodiesels. Turbodiesels generally don't have a wastegate at all, they are operating under boost whenever they're far enough above idle for the turbo to create positive pressure in the intake. They use the turbo to provide a greater air charge for the same overall displacement of the engine, effectively increasing the compression ratio. In compression-ignition engines, higher compression ratios generally yield higher efficiency.
Gasoline turbocharged engines typically aren't operating under boost in lower-demand operating conditions and transition to positive pressure in the intake only when necessary.
So, when you have a bigger engine set up intentionally for high-load usage (with the transmission and differential ratios selected accordingly) it can do more without requiring boost. That fits with what Andrew T said about box trailers vs. Airstreams with the F150 Ecoboosts... the box trailer's higher aero drag causes the truck to need the turbo more, where the Airstream only needs much boost for climbing hills.