Okay, now the carmakers say they get it. Americans want better fuel economy, and they want it now. And just to make sure that message was received, last December Congress passed a law that requires fleet mileage of 35 mpg by 2020.

So how does the industry plan to get there? Despite what many green consumers might like to think, we won’t all be driving electric cars—or even hybrids—next year. Hybrids may be a much larger portion of the market by 2015—GM exec Bob Lutz says it may be 30 percent, certainly higher than the current 2.5 percent—but large numbers of cars between now and 2020 will still be fueled by plain old gasoline.

Within a couple of years, however, they will be much, much more efficient with that gas. And one way they’ll do it is with a new technology that’s about to spread like kudzu: smaller engines with gasoline direct injection, or “GDI.”

Rather than mixing gasoline with air in an intake manifold before it’s sucked into the combustion chamber, a GDI engine’s fuel injectors squirt the gas directly into the cylinder. Modern electronics now allow very, very precise calculation and metering of each separate injection. And remember, if the engine is turning at 3,000 rpm, there are more than 10 such injections every second.

Older engine electronics simply weren’t fast enough to look at all the data about everything happening in the engine, and then calculate the right amount of fuel for each cylinder and have it squirted in on time. And those injectors were too pricey to use when gasoline was $2 a gallon or less.

But injection is just half the picture. GDI engines are smaller than regular ones, but they put out the same power because many (though not all) are also turbocharged. A turbo is a small pump, driven by exhaust gases, that packs more air into each cylinder. That allows more fuel to be used, producing greater power—but from a much smaller engine than a non-turbo with the same power.

The combination of direct injection and turbocharging are similar to techniques used to make modern passenger diesels smaller, smoother, more powerful, and cleaner than earlier versions. Now gasoline engines will travel the same path.

Building on their diesel experience, European carmakers already sell non-turbocharged GDI engines in many home-market cars. Now they’re starting to appear in export models too; Volkswagen offers a 200-hp, 2.0-liter GDI engine in its new Tiguan small SUV, for instance. But GDI will be a tidal wave, and it’s coming fast.

Ford calls its GDI system EcoBoost, using it to produce the power of a V8 from its 3.5-liter V6 engine. According to Dan Kapp, Ford’s director of power train research and advance engineering, it will provide 15 or 20 percent better fuel economy. EcoBoost will first appear in the 2010 Lincoln MKS luxury sedan, then it’ll move into Ford’s large pickup trucks. That engine, by the way, actually produces more torque (340 ft-lbs versus 310) than today’s 4.6-liter Ford V8. Ford recently said it will offer EcoBoost engines on more than 80 percent of its lineup by 2012.

GM, on the other hand, will use GDI more as the Europeans do. The company’s first GDI engine for the US will be a “Family Zero” 1.4-liter turbocharged GDI for the Chevrolet Cruze, a global subcompact to be introduced at the Paris Motor Show in October. That car will be built from 2010 in Lordstown, Ohio, for the US market, replacing the Cobalt for 2011. GM has estimated a fuel economy of 45 mpg, a substantial increase over the Cobalt’s 25/36 ratings when fitted with the most modest engine, a 2.2-liter Ecotec.

And, it turns out, a far more glamorous vehicle than the Cruze will also use the same engine. While the Chevrolet Volt concept vehicle contained a European 1.0-liter, three-cylinder gasoline engine, press reports now say the production version in late 2010 will use the same engine as the Cruze. GM has filed paperwork to build an engine plant of half a million square feet in Flint, Mich., to produce 1.4-liter GDI engines for the Cruze—and, apparently, for the Volt as well. That motor, however, will use standard induction, according to GM spokesperson Rob Peterson—contradicting earlier reports that the Volt’s engine would be a turbo as well.

In the next five years, in fact, turbocharger manufacturer Honeywell projects that globally, engines with turbos will grow from 30 to 38 percent of the total by 2013.