Mazda is cutting the advertised horsepower figure for its crucial new rotary-engine-powered RX-8 sports car in the United States, according to WardsAuto.com.

A Mazda spokesman told WardsAuto.com that the new, four-door RX-8, powered by the company's signature engine that uses trochoid-shaped rotors instead of conventional pistons, makes slightly less power than originally billed - the higher-power version of the rotary produces 238 hp rather than the 247 hp Mazda originally specified while the lower-power rotary, sold with automatic transmission, develops 197 hp instead of the 207 hp Mazda first indicated.

The spokesman told WardsAuto.com that the difference comes from actual horsepower figures derived after emissions certification from the US Environmental Protection Agency while the original horsepower figures were estimates developed prior to the actual EPA certification process.

The RX-8 officially went on sale in early July and customers who already have taken delivery or who ordered the car prior to August 26 will be offered free scheduled maintenance for the new car's entire warranty period - worth an estimated $US1,200 - and be given a $500 debit card, WardsAuto.com said. If owners still believe they've been irrevocably wronged, Mazda will buy back the car for the original purchase price, the report added.

Mazda stresseed that although the horsepower figures are marginally lower (3.6% for the high-power rotary and 4.8% for the lower-power variant), the RX-8's performance is unaffected, WardsAuto.com said.

In 2001, WardsAuto.com noted, Mazda overstated the horsepower of the slightly revised four-cylinder engine in its Miata roadster(MX-5) and struck a deal with customers similar to that now presented for the RX-8.