What You Should Know About Horsepower Ratings

Studious car shoppers may have noticed that horsepower and torque ratings on some vehicles changed slightly in the past year. The 2005 Acura TL made 270 hp and 238 pounds-feet of torque, but the 2006 model is rated at 258 hp and 233 pounds-feet. Toyota's 2005 Sienna minivan made 230 hp; this year, it drops to 215 hp.

Rest assured these vehicles perform identically to last year's models. Automakers are not turning down the heat — rather, they are measuring it differently. In April 2005, the Society of Automotive Engineers tightened rating guidelines, calling for all tests to include an SAE-approved witness as well as standardized conditions for fuel, airflow and engine load. SAE, whose procedures for rating engine output have been the unofficial industry standard since 1980, says previous criteria allowed automakers too much wriggle room. General Motors was first to adopt the new standard, announcing in 2005 that the Chevrolet Corvette Z06 produced 505 SAE-certified hp.

Although compliance is not required, many automakers have since jumped on board. Effects vary: The 2006 Dodge Viper saw a slight power increase, while the TL, Sienna and Mazda RX-8 took modest hits. Other models, such as Acura's TSX, received engine upgrades as well as SAE certification for 2006. The TSX posted a 5-hp gain that reflects a combination of SAE rating standards and mechanical improvements.

Look for SAE certification to appear in more vehicles over the next several years. In the meantime, it's difficult to accurately compare certified and uncertified numbers at face value. But remember that horsepower and torque mean little without considering weight, aerodynamics and the car's transmission. The numbers might make for good small talk, but real-world performance is what counts.

Posted on 4/5/06