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Buyers who want to maximize fuel economy and reduce tailpipe emission, including CO2 (carbon dioxide), might want to look for these high-tech features designed to increase fuel economy:

Cylinder deactivation

In a typical passenger car, the engine requires only about 30 of its available 200-plus horsepower at highway cruising speed. This so-called light-load condition is the perfect time to put as many as half of an engine's cylinders to sleep. The idea is to convert, for example, an eight-cylinder engine to a more economical four-cylinder one on the fly.

When you need full power for towing or accelerating, sophisticated electronics instantly "wake up" the sleeping cylinders. The system improves fuel economy by 7 to 20 per cent.

In the past, cylinder deactivation caused unacceptable roughness in smaller, four-cylinder engines. But advances in technology have changed that.

Today, several auto makers apply cylinder deactivation to their V-6s and V-8s. For example, General Motors calls its system Displacement on Demand or Active Cylinder Management; DaimlerChrysler, Multi-Displacement System ; and Honda, Variable Cylinder Management.

Direct fuel injection

With conventional fuel injection systems, the engine mixes fuel and air and then spritzes the resulting mist into the combustion chamber. Imagine a cologne atomizer and you get the picture. This is not the most efficient way to create combustion.

Now several car makers have worked on direct-injected gasoline engines that shoot fuel straight into the combustion chamber and then introduce air. Usually, they also employ a turbocharger (a kind of fan driven by exhaust gases) or a supercharger (a similar fan driven by the engine itself) to get more air inside the chamber.

Direct injection allows better control of the timing and shape of the fuel-air "cloud" so that it can burn more efficiently.

The key to all this is the sophisticated electronic controls designed to vary the amount of fuel injected, depending on driving conditions. All this translates to more power, lower emissions and better fuel economy — as much as 15 per cent better, in fact.

Auto makers currently offering vehicles with direct-injection gasoline engines include Audi (A3), General Motors (Pontiac Solstice GXP and Saturn Sky Red Line), Mazda (Mazdaspeed3 and 6 and CX-7) and Toyota (Lexus IS 250 and GS 300). More are coming. For instance, BMW intends to use direct injection on all of its models eventually.

Automatic idle-off

Drivers burn an estimated 15 per cent of their fuel while stopped at red lights or idling in traffic. With an integrated starter generator, computer controls shut off the engine in such situations. Simply touching the accelerator restarts it in much the same way that touching the keyboard or mouse restarts a laptop in sleep mode.

This technology has been well adopted by gasoline-electric hybrids such the Ford Escape, Honda Civic and Toyota Prius. All employ idle-off technology, using the hybrid's regenerative braking system to charge a battery that powers restarts. But conventional gasoline engines can also use idle-off. GM offers it on full-size pickups. Because they use regenerative braking, such vehicles are sometimes referred to as "mild hybrids."

Transmissions with more gears

Generally, manual transmissions yield better fuel economy than automatics. But the more speeds that an automatic has, the better the fuel economy.

Today, sophisticated six-speed automatics have become increasingly common and Lexus even offers an eight-speed automatic on the LS460 luxury sedan. The large number of gear ratios allows the transmission's electronic controls to choose the most efficient gear for a particular situation.

Transmissions with no gears

If more gears equal better fuel economy, then the continuously variable transmission (CVT) is perhaps the ultimate solution for delivering excellent fuel efficiency.

A typical CVT does not have four, or five or six or more fixed gear ratios. It uses a pulley that slides along the engine shaft and one that slides along the driveshaft, with a belt connecting the two. Rather than shifting from gear to gear in discrete steps, a CVT's pulleys move smoothly along their shafts to yield a theoretically infinite number of gear ratios. The arrangement keeps the engine in its most efficient range, improving overall fuel economy by as much as 10 per cent.

CVTs were held back for years, largely because engineers had trouble finding belts durable enough for a powerful engine. But flexible steel and other tough materials have made CVTs practical on passenger vehicles. Audi, Ford, Honda, Mini, Nissan and Saturn offer the gas-saving transmission in some of their models.