I had noticed that all the listings of the GS550 M Katana has no(z). I own a 1982 550 Katana and the top speed on here is listed wrong, the BHP is listed wrong as well. I have the Suzuki service manual straight from the factory. It´s listed in my manual as 56 BHP, and a top speed of 118 mp/h. I had my exact bike with 72,000 kms on it and after new piston rings, and a valve job, up to 195 in top gear and maybe had 1000 RPM left. I don´t know if the (z) in my model name means anything different, if so someone pls let me know. To all the Katanafans "Keep it alive"