My experience with a Subaru turbocharged car (1800cc engine) was 7 to 8 kilometers per litre for everyday use, and as low as 4 kilometers per litre when pushed hard, which is not as good as a car designed for spirited driving with an NA 3000cc to 3500cc engine such as the 330i and G35. Of course the Subaru engine is of old design using gasoline evaporation cooling (overly rich gas/air mixture to let the unburnable gas to evaporate inside the combustion chambers).
Even with a more efficient modern turbocharged engine, no matter how gingerly you drive the boost comes on occasionally burning more gas, therefore a 2000cc turbocharged I-4 engine certainly always consumes more fuel than its NA 2000cc I-4 siblings. Even when cruising at a highway speed with little or no boost, the car is driven by a low compression ratio engine (9.2:1 in the case with RDX) burning premium gas with somewhat restricted exhaust channel. Therefore, it is wrong or at least misleading to make such a statement as “It allows the RDX to deliver the power (240 horses) and torque (260 lb-ft, the most of any Acura ever offered) of a larger six-cylinder engine along with the fuel economy of a four-cylinder.” The only advantage of an I-4 over similarly performing V- or I-6 is that the I-4 has less internal friction and, possibly less weight.
Honda learned a lot about turbocharging when F-1 race cars were powered by 1500cc turbocharged engines. Honda was so successful that Europeans cunningly changed the rule resulting in Honda getting out of the race for a while. Because of what they learned from the F-1 engine they have NOT applied turbocharging to ordinary passenger vehicles (with the exception of earlier CIVIC models). Now comes RDX. Honda must have found something that they feel comfortable with blowing its 2300cc I-4. What is it? Do we know? Do they use piezo activated direct-to-cylinder fuel injection? Does the injection occur twice or more per combustion stroke? Do they use throttle valve and port fuel injection along with the direct-to-cylinder injection? And, most importantly, is there a delay in the closing timing of the intake valves making the effective compression stroke shorter than the expansion stroke? I want to know.
