Kawasaki’s introduction of a Z900RS at the Tokyo Motor Show in October 2017, elicited gasps of excitement and, no doubt, a few pangs of nostalgia from those who remembered the first edition. In the early 1970s, there were two Japanese street bikes that really pushed the performance needle. One was the Honda 750-four, which brought inline, four-cylinder power to the mainstream. The other was even more fierce: Kawasaki’s 900 Z1, which, when it was rolled out in 1972, was the fastest and most powerful Japanese production motorcycle ever built. Its reported 81 horsepower and 54.2 pound-feet of torque are a bit tame by today’s standards, but the Z1 was the beast of its time, with a top speed of about 130 mph. Its smooth power delivery, nimble handling and potent inline acceleration made the Z1 an instant favorite with track racers, drag racers and street racers alike. Power from the air-cooled, double overhead cam engine was channeled through a five-speed transmission and the bike had a wet weight just under 550 pounds. In subsequent years, Kawasaki squeezed even more power out of it, and its suspension and frame were improved up until it gave way to the new KZ900 in 1976.