Their logic is borderline insane. We put teeny tiny turbo engines into 3-4,000 lb cars, over work the engine so the turbo is always in demand, everyone knows high boost events guzzle gas... but this is fuel efficient.
Put the biggest motor possible into the smallest car possible and voila fuel economy. Hit the nail with a sledge hammer not a feather duster...
This is a flawed argument.
A small displacement engine that is turbocharged can easily flow more air than a large displacement naturally aspirated engine.
The small displacement engine has less parasitic loss, has scaleable power output and smaller diameter cylinders have less stress on them under boost than large diameter cylinders that are naturally aspirated.
The problem is the person operating the vehicle that wants full power all the time from that little engine with a turbocharger, so it happily consumes the fuel needed to match the air flow. If the operator was capable of exhibiting restraint, the small displacement turbocharged engine will always achieve better economy than a comparable large displacement engine.
In the same way, the ISV will outperform the Duramax, the Powerstroke and the ISB.
As with everything there is a balance point of needing sufficient displacement for the basic needs of the vehicle before the turbo spools.
The biggest possible engine has higher friction, higher weight, higher parasitic losses and higher fuel consumption at low power requirements.
