SAE What?

THE SOCIETY of Automotive Engineers recently revised the rules for measuring horsepower and torque and introduced a new standard for certifying said numbers. It's been a quiet revolution, unlike the one in 1971 that made gross horsepower ratings (measured on a stark-naked engine) obsolete by introducing net ratings (testing an engine wearing its alternator, vital-fluid pumps, and intake and exhaust systems). There's no mathematical correlation between gross and net, but the original standard lowered ratings by roughly 20 percent, which provided welcome camouflage for power output ratings already in free-fall during those early dark days of emissions control.

This latest revision to J1349 won't uniformly cut everyone's engine ratings. In fact, the first engine certified to meet the revised standard--the Corvette Z06's LS7 V-8--got a five-horsepower increase to 505. The point of the revision is to account for new engine technologies and to reduce the opportunity for liberal interpretation.

GM's Dave Lancaster, who chaired the SAE committee that drafted the standards, claims that by taking advantage of the biggest loopholes it was possible to inflate SAE net results more than 15 percent (approaching gross output). Modern engine controllers didn't exist in the 1970s, so it wasn't specifically prohibited to run special spark and fuel curves during the test. Using the recommended fuel grade wasn't required, so by running premium in a regular engine with a souped-up spark map, several stray horses could be lassoed. Power-steering pumps could be left off, extra-deep oil pans that prevented windage losses were allowed, exhaust and intake restrictions were poorly defined, and correction factors for temperature, pressure, and even a transmission could be manipulated.

Manufacturers committed to reporting accurate, representative numbers all along won't be affected by the changes. Conversely, any manufacturer that lowers its output ratings in the near future will be under suspicion of having gamed the system.

Inviting a neutral third-party SAE witness to certify an engine's output is the surest way to dispel doubts and win customer confidence. The certification procedure is patterned after one in Europe. Lancaster explains, "We found that their advertised numbers more consistently aligned with the [engine test] results we measured. We wanted to bring that repeatability to the United States." The standard spells out the qualifications for the witness and requires the manufacturer to test a production or production-intent prototype engine, documenting all input variables and output statistics, and filing the information with the SAE. The certified output must be within one percent of the dynamometer output. Of course, ringer engines could easily be slipped through this process, but by certifying an engine the manufacturer guarantees all production engines will produce within two percent of the rated output (Europe allows five-percent deviation).

General Motors plans to certify every new or significantly revised engine in the future. Frank Fsadni, Ford director of V-engines, says his company has no plans to certify any engines. Instead, Ford pulls three engines at random from the production line and runs three tests on each, then reports the average of these nine tests. The Chrysler group is still considering whether to certify all engines or just high-performance ones.

In 1971, the industry shifted to reporting SAE net. This new certification standard is voluntary, and engine manufacturers (and performance tuners) should follow GM's lead. We'll credit those engines that meet this higher standard by indicating "SAE certified" in our spec panels.