I really don't know my mpg on my 08 Z1000, but I do know that it goes up a little once the engine breaks in. As for octane ratings, the second gen reqires 91 min.. Stick to this!! I don't know about 1st gens, but it's prolly the same. Octane req. have NOTHING to do with how expensive your vehicle is (Honda vs Duc), or how much HP you have (generally speaking). It's all about the Compression ratio of the engine. If your motor makes 8.7:1 comp and the factory says 87 octane min., then using 91 or race gas will get you ABSOLUTELY ZERO increase in HP, Tq or mileage. Period. Octane additives, (the amounts defined in octane ratings: 87,89,91,93, etc.) are put in to prevent "detonation", which is the a/f mix lighting up due to pressure, before the spark plug lights it up. The higher the compression ratio, the sooner the fuel will generally ignite, so the higher the required octane. In old school terms, a run of the mill 8:1 chevy 350 runs on 87 octane (reg) unleaded. To this day, almost every car or truck sold in this country is designed to run on reg.. Putting 91 in does NOTHING. BUT, if you swap out the 76cc heads for 64cc's, or swap the dished pistons for flat-tops, or change the thick cork head gaskets to thin copper "shim" gaskets, you will increase the compression and the fuel/air will ignite due to pressure, before the ignition (spark) sets it off. This is usually just known as "knocking", but at it's worse it will destroy your motor. In a turbo or supercharged engine the "mechanical" comp.is lowered, say 8.7 down to 8.0, but the boost puts it much higher, and thus needs higher octane not to lose power/burn up pistons. LONG STORY SHORT, find out what the factory says your engine needs, and use that. If you use less, you will damage your engine and/or lose power at the least. Use higher and you're just wasting money. Many auto mechanics don't understand this ****. 07-09's need 91 octane. 1st or 3rd gen.s, ???
Note: this is info I've picked up over the years from the tech guys at Comp Cams, Summit Racing, Felpro gaskets, Chevy performance, etc etc, All talking directly to me about projects I was working on, as well as a few motors I've ruined before I knew about this. I am not a mechanic or expert, just a hobbyist that tries to do it right and understand the actually theory before I buy the wrong part(s).