using Reed-Valves in intake ducts. In two-stroke engines, metal reeds last about while carbon fiber, around . This poor combustion in the trailing side of the chamber is one of the reasons why there is more carbon monoxide and unburned hydrocarbons in a Wankel's exhaust stream. A side-port exhaust, as is used in the Mazda Renesis, avoids port overlap, one of the causes of this, because the unburned mixture cannot escape. The Mazda 26B avoided this problem through the use of a three spark-plug ignition system. Regulations and taxation National agencies that tax automobiles according to displacement and regulatory bodies in automobile racing use a variety of equivalency factors to compare Wankel engines to four-stroke piston engines. Greece, for instance, taxed cars based on the working chamber volume (the face of one rotor), multiplied by the number of rotors, lowering the cost of ownership. Japan did the same, but applied an equivalency factor of 1.5, making Mazda's 13B engine fit just under the 2-liter tax limit. FIA used an equivalency factor of 1.8 but later increased it to 2.0, using the displacement formula described by Bensinger. Car applications The first rotary-engined car for sale was the 1964 NSU Rotary Spider. Rotary engines were continuously fitted in cars until 2012 when Mazda discontinued the RX-8. Mazda has announced the introduction of a rotary-engined hybrid electric car, the MX-30 R-EV for a 2023 introduction. NSU and Mazda Mazda and NSU signed a study contract to develop the Wankel engine in 1961 and competed to bring the first Wankel-powered automobile to the market. Although Mazda produced an experimental rotary that year, NSU was the first with a rotary automobile for sale, the sporty NSU Spider in 1964; Mazda countered with a display of two- and four-rotor rotary engines at that year's Tokyo Motor Show. In 1967, NSU began production of a rotary-engined luxury car, the Ro 80. NSU had not produced reliable apex seals on the rotor, though, unlike Mazda and Curtiss-Wright. NSU had problems with apex seals' wear, poor shaft lubrication, and poor fuel economy, leading to frequent engine failures, not solved until 1972, which led to large warranty costs curtailing further NSU rotary engine development. This premature release of the new rotary engine gave a poor reputation for all makes, and even when these issues were solved in the last engines produced by NSU in the second half of the '70s,