If you’ve read op-ed pages in newspapers lately or spent much time online, you’ve probably seen these complaints: Why can’t U.S. car buyers get the same high-miles-per-gallon vehicles that are sold in Europe? And why do U.S. automakers seem to make high-mpg cars elsewhere but not here?

As late-night TV host Johnny Carson might have put it, “Not so fast, there, ethanol breath.” Those who advocate shipping European high-mpg models to American shores apparently don’t realize those vehicles would probably be seized at the port of entry: They do not meet U.S. NOx emissions standards. (Movie-going readers may recall a similar fate befalling the Tom Cruise character in the Oscar-winning flick Rain Man.) At least for now, NOx regulations are tougher here than in Europe or Asia.

Moreover, it is quite possible that the alterations needed to hit stringent NOx levels would eliminate some of European vehicles’ mpg advantages. A portion of NOx emissions get taken care of with catalysts in the exhaust system. But part of it has been handled by reducing compression ratios and adjusting ignition and valve timing. This, in turn, reduces engine thermal efficiency. All in all, such measures can degrade mpg performance. (Thanks go to reader Wayne Baldridge for pointing out these relationships.)

I asked the Big Three whether their efforts at meeting NOx regulations work against efficiency in their U.S. models. They reacted as though I had poured oil on the track at a motorcycle meet. The automakers, normally responsive to technical questions, wanted nothing to do with me. All I could get out of Ford was, “We fully understand we must achieve both NOx emissions regulations and improve fuel efficiency within our product lineup. That’s it for us.” GM and Chrysler both clammed up completely. Nor would the EPA respond to queries along these lines.

Since the Big Three won’t talk to me, I don’t know why they won’t address NOx/mpg trade-offs. But I have a hunch. They probably figure an NOx/mpg discussion is a no-win situation. There’s a risk it would alienate EPA decision-makers with whom automakers have cultivated cordial relations. Besides, much of the U.S. populace would be too technically unsophisticated to grasp the concepts involved.

Other factors can inflate European mpg figures. One is never sure, for instance, whether mpg ratings for specific foreign cars are being expressed in Imperial or U.S. gallons. A rating in Imperial gallons, of course, would look about 20% better.

And lest you think there is something inherently better about foreign engine technology, consider this: European automakers have their share of troubles here coaxing out mpg when they try to sell anything but small cars. In 2006, for example, BMW paid over $5 million in fines for not meeting U.S. CAFE regulations. Volkswagen chipped in about $1 million that year. The biggest scofflaw was DaimlerChrysler which anted up over $30 million in penalties, though it is not clear how much of that was from its imported vehicles.

Finally, U.S. automakers have taken heat over the size of the engines they put in their cars. The reality is that 85-hp vehicles haven’t been able to deliver what U.S. customers have wanted: Not specifically muscle cars, but a means of transportation that can accelerate smoothly from on-ramps into 65-mph freeway traffic.

— Leland Teschler, Editor