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I have been using 91 octane since the day I bought my bike. Don't ask me why, but I switched to 89 octane today. 5 minutes later I noticed my bike running smoother, and faster with less throttle. Later on I took the bike out for another ride, had forgotten about the octane change and still noticed how unbelievably smooth it was running. Then I remembered the 89 octane. Am I Crazy!? or can lower octane be better for an engine like the ZR-7s? I literally feel like I have a new bike. Maybe I should try 87 octane? I have a Toyota Avalon and it runs significantly better on HIGHER octane. The bike on LOWER octane. Can anyone explain?
 

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Which octane is best depends on several factors but primarily on compression ratio, head design and ignition advance, but normally the rule is higher compression ratio=higher octane.
If you can run on a lower octane WITHOUT pinging and detonation then using a higher octane is just a waste of money. It is often erroneously thought that using a higher octane gives more power.
Having said all that over here we're spoilt for choice. Either LRP (lead replacement petrol) or Lead Free. That's it.
 

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High octane gas has no more potential energy than does 87 octane. So, no more power. The only difference is its resistance to knock. Our bikes are designed to run on 87 octane, and, as the gas companies were forced to admit after a Federal Trade Commission action (U.S.), there is no significant benefit to running premium gases in engines designed for 87 octane. These premium gases do not provide more power or clean the engine better in practice. Soap is soap! In fact, engines that are designed to run on 87 octance will often perform WORSE on premium grades due to the slower flame pattern. I have read that this is especially true in air cooled motors.
 

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My guess is that you just got a better batch of fuel, even if it was from the same station. Consider this, there is no actual tank for the midgrade, it is actually mixed at the pump about 70% reg and 30% prem. Since the price of fuel has been high very few people want to pay even more for prem. There's lots of very stale (and wet) premium out there IMO. So if buying the 70% fresh stuff (89) made her run good, think what the 100% (87) would have done? LOL! Like everyone states the zr is fine on 87 if your not lugging it up a hill riding two up, I'd shy away for any 85 though. If your running an advanced rotor I might tend to go up a fuel grade.
 

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In the morning here it's 5 Celsius. So I like starting my engine with 91 octane, and less chances of rust. Never by gas at a discount station (risk of water and debris).
 
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