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Choosing the Right Engine Size

2/24/2012
Deciding which new vehicle to purchase is made more difficult by the wide array of engines available for each model. A buyer might think small engines offer better fuel economy while larger engines will deliver performance. In truth, fuel economy isn't always proportional to engine , and big engines don't always provide the best performance.

To better understand which engine is best for your needs, it helps to understand the relationship between engine , horsepower and torque. It also helps to understand government fuel economy guidelines.

Horsepower, torque and engine
Horsepower is the amount of force an engine can produce. Torque is how that force is applied to turn the wheels. In almost all cases, increases in horsepower and torque come at the expense of fuel economy.

Small engines, with fewer cylinders, traditionally have less horsepower and torque. As a result, they burn less fuel. Because they are smaller and more fuel-efficient compared to their large-displacement counterparts, these engines often weigh less. This allows the vehicle to handle better. Smaller engines will have fewer parts to service and be less expensive to maintain during the life of the vehicle. Small engines should not necessarily be considered underpowered. Turbochargers or superchargers can make smaller engines very powerful, while consuming less fuel than larger engines.

Engines with six or more cylinders are generally more powerful than smaller engines. With larger cylinders and increased complexity, this type of engine burns more fuel to generate the horsepower and torque needed to move heavy loads or pull a trailer. For towing or carrying large loads, consider an optional diesel engine. Today's diesel engines are quiet and cleaner-burning than those offered in the past, and generate plenty of power with reasonable fuel economy.

Understanding CAFE guidelines
Fuel economy information is listed on the window sticker of every new vehicle sold in the United States, as required by the federal government. The guidelines, known as Corporate Average Fuel Economy (CAFE), were introduced following a Congressional Act in 1975, with the first standards taking effect in model year 1978. CAFE was designed to reduce energy consumption by requiring manufacturers to increase the fuel economy of their cars and light trucks. Under the CAFE program, a test cycle is used to estimate city and highway fuel consumption in miles per gallon (mpg), and the test results are listed on the vehicle's window sticker.

CAFE ratings should be used only as a guide to fuel economy. The old CAFE ratings were based on a now-obsolete series of tests, and most consumers found their actual mileage to be lower than that listed on the window sticker. More than three decades after enactment, CAFE testing has been updated to better reflect real-world driving conditions for model-year 2008 vehicles. Consumers now see the revised CAFE numbers for all 2008 model-year vehicles. In addition, the CAFE numbers for older model-year vehicles (2007 and earlier) have also been revised on the EPA's Web site to reflect the new numbers. These new mpg ratings reflect estimates of acceleration and faster speeds, the use of air conditioners, and colder outside temperatures. They are generally a few mpg below previous ratings, but are more relevant to real-world driving conditions.

Making the decision
When choosing your next engine, take a close look at the CAFE ratings on the window sticker and the engine specifications in the brochure. The differentials in horsepower and torque between engine s may not be enough to justify a price premium. While each type of engine operates differently, their fuel economy, horsepower and torque ratings often reveal much about how they will perform.

In December 2007, the U.S. Congress passed an energy bill that requires cars to have an average fuel efficiency of 35 mpg by model year 2020. This is the first increase in fleet fuel economy passed in the past 32 years.

Want to learn more about fuel economy? For more information about CAFE standards and fuel efficiency, visit the Environmental Protection Agency's Web site (www.fueleconomy.gov).