Trucks are large and powerful for a reason: They are designed to haul heavy loads and pull trailers. Their sheer size translates to more mass, which in turn means a less-efficient vehicle even when empty.

The formula in the old days was to use a more powerful engine tuned for pulling performance without much regard for fuel mileage. These days, automakers know their biggest vehicles are the biggest consumers and are working to make them more refined and efficient.

Here’s a look at current and future technology Big Three engineers are employing in light-duty pickups and truck-based SUVs.

Engine refinements once reserved for high-end luxury and performance autos are finding their way into truck power plants. Variable valve timing optimizes the amount of fuel and air that enters the combustion chambers depending on need and has been incorporated in the next-generation 5.7-liter Hemi V-8 engine in Dodge trucks and by General Motors in a new 6.2-liter V-8. Ford also uses variable valve timing in the Triton 5.3-liter V-8 as well as a freer-breathing three-valve-per-cylinder arrangement. Each of the Big Three’s truck engine offerings includes E85-capable V-8s.

Cylinder deactivation is another technology seeing increasingly widespread use in the truck world with Chrysler’s multidisplacement system and General Motors’ active fuel management on select engines. It takes a lot more power to get a vehicle rolling than it does to maintain a steady speed, so these systems seamlessly make V-8s run on four cylinders in low-demand situations. A new Dodge Ram can cruise at up to 70 miles per hour in four-cylinder mode.

While Ford does not offer a cylinder deactivation system, it does have a deceleration fuel shut off feature to help save gas when the driver is off the throttle. Taking that a step further, GM and Chrysler have both toyed with a mild hybrid feature in trucks, now sometimes referred to as auto stop/start. Consisting of a starter/generator and larger battery pack, these systems completely shut off the engine when coming to a stop and use that rolling and braking energy to recharge the batteries. The engine remains stopped for up to several minutes while batteries run the accessories, and the system automatically restarts the engine when the driver lifts his or her foot off the brake pedal. Expect this technology to make a comeback in trucks.

Ford and GM are also successfully coupling larger V-8s to new six-speed automatic transmissions, allowing them to use higher rear axle ratios that increase fuel efficiency by reducing engine speed.

Aside from engine and powertrain technology, aerodynamics is another area where the battle between truck makers has heated up. Aerodynamic enhancements, as well as the use of some reduced weight components, are the basis for two new fuel-saving packages by Ford and GM. Ford’s SFE (superior fuel economy) and GM’s XFE (for extra fuel economy) pickups both claim 15 mpg city and 21 mpg highway.

For 2009, the Chevrolet Silverado and GMC Sierra 1500 pickups will be offered in hybrid versions. This two-mode hybrid system was jointly developed with Chrysler and BMW and will find its way into Dodge Ram 1500 pickups for the 2010 model year. It is already available in Chevy Tahoe, GMC Yukon, Cadillac Escalade, Dodge Durango and Chrysler Aspen full-size SUVs.

Unlike other hybrids, the two-mode system is designed for vehicles that need a lot of capability. It’s powerful enough to run a full-size truck up to 30 miles per hour on electric power alone, and the electric drive can be automatically bypassed for pure mechanical power in situations of high demand like towing and hauling. The manufacturers claim a 40 percent fuel savings in the city and 25 percent overall.

Diesels have been the engines of choice in heavy-duty trucks for their greater fuel mileage and better torque characteristics, but a diesel in a light-duty pickup has been rare. That’s about to change with GM’s announcement of a 4.5-liter V-8 diesel slated for light trucks in 2010. Dodge Ram 1500 will also see the availability of smaller light-duty diesel from partner Cummins after 2010.

Ford hasn’t released a lot of details, but a new clean diesel engine is planned for the F-150 in 2010. Additionally, the 2010 F-150 will see another promising new engine, a twin-turbocharged, gasoline direct-injection V-6. Called EcoBoost, this technology isn’t exclusive to Ford but it might be the first to bring it to market in a wide array of vehicles. While some old-school truckers might be skeptical, this engine sounds ideally suited for truck use, with V-6 fuel economy and high torque that rivals a V-8. The torque is available at lower engine speeds, much like a diesel.