It is possible. I rented a large Buick a few years ago (I can't remember the model name now, but it was, I believe, the largest model) for a trip from Corning, NY to Boston. I drove 70-75 both directions and that car got 31 MPG for the trip! I was amazed. My minivans never got above 27 on a trip and typically got 25 at those speeds.
However, that car may have been terrible in local driving, I don't know. My minivans got 22 or so in local driving, they just never got much more than that even on a trip.
In some areas, the gas pumps are checked for accuracy, and the station gets dinged if they don't deliver the full indicated amount. So, the station may be setting them to deliver slightly more than the indicated amount. This would inflate your hand calculations of MPG.
Your Chevrolot Classic has that relatively new Ecotech 2.2 L4 in it. I have one in an Olds Alero ('03).
Relatively smooth engine, and pretty good power for a four. A VERY low maintenance engine. But mileage has been unimpressive with this engine, and that seems to be no matter what car it is mated to.
I agree you may like the 4-cylinder Sonata better.
I read an interesting article detailing the current EPA fuel economy calculation. It is performed in a lab, by the manufacturer on a dyno. It does not factor in use of accessories, wind resistance, and traffic lights. There are preset times for the lab/driver to change speeds, stop, etc. I seem to remember there are some regulations on which fuel can be used but that may only be in the proposed new standards. At any rate, I am sure the manufactuer is using the cleanest, best fuel allowed. I bet they make sure ambient temp is in the most favorable range as well.
I am approaching 9,000 miles on my 2006 Sonata V6 with an average of 21 mpg in mixed driving. On a highway trip it once briefly passed 30mpg but I notice that it quickly drops to around 27 mpg at higher speeds. By the way I think the EPA test top speed is 40 or 45 mph!
I stopped manually calculating mpg after several fillups when I noticed the Sonata's computer was only tenths of a mpg different from mine. One fill-up it exactly matched my calculation.
I think we're barking up the wrong tree. I don't think the engine is the problem.
Having studied the various competitors, I notice the Sonata is heavier, wider, and has higher ground clearance than comparable cars.
There's no free lunch. Weight alone is costly. All other things being equal, a 3200 pound car's (Sonata V6) gas mileage will be at least 1-2 MPG worse than a 2900 pound car (Camry V6).
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