The second generation MX-5 was unveiled in 1997 and put on sale in 1998 for the 1999 model year. While it kept the same proportions of its predecessor, its most noticeable change was the removal of the retractable headlamps, which were eliminated in the face of more stringent pedestrian safety tests. The NB model of the MX-5 featured a slight increase in engine power, a refined interior design and the option of a six-speed manual transmission. In 2001, the model underwent revisions, the second generation boasted a slight increase in engine power, a more refined interior with an updated design, and a newly available six-speed manual transmission. In 2001, further revisions included slightly updated front and rear styling as well as variable-valve timing engine technology for the 1.8-liter engine, which now made 106 kW (142 hp). Updated models have since been known as NB2, while the earlier versions are referred to as NB1. While various special editions continued to be introduced throughout the entire NB production run, the Mazdaspeed MX-5 is distinctive for being the only MX-5 to be turbocharged at the factory. The Mazdaspeed variant, built for the model years 2004 and 2005, made 133 kW (178 hp) from a turbocharged version of the normal 1.8-liter engine, enabling a quarter-mile time of 15.2 seconds and a 0–97 km/h (0–60 mph) time of 6.7 seconds. Other Mazdaspeed specs include stiffer and shorter springs, Bilstein shocks, and larger 17-inch wheels.