Octane??

[Hoomgar]

Right on Amos. One thing (if you know my take on this subject) that you will notice I didn't comment on as I am not done testing it yet is fuel economy.

I "think" it may be better or the same. It is my experience regardless what anyone says that when your running a grade of fuel that your engine runs noticeably better on that you get better fuel economy. It is running better on this stuff for sure so I am expecting it to get better economy or at a minimum stay the same. So far, it looks like it may be better but I don't use two tank fulls as a positive test. I am going to post on that later when I know for sure.

[Dave_A]

1. Octane does not increase HP.
2. Use what is specified for your machine.
3. If your bike pings on 87 octane, you can usually retard the timing slightly (with subsequent loss in performance) and eliminate pre-detonation.
4. Use of high octane fuels may cause poor idling when cold and unexplained stalling.
5. Using premium in a low to mid compression engine is a waste of money!

Interesting. But what is considered high compression? 9 to 1? 10 to 1? More?

In auto circles, 10.1 is the general 'mark'...

My Z28 is 10.5.1 stock -> GM says 91 or higher octane only...

Of course, in a modern car, pinging/detonation is less of a threat because the ECM automatically retards the timing when this is detected... So running cheaper gas -> worse perfromance and fuel economy (due to timing retard), more than engine damage...

The thing is, old bikes do not have ECM units... So if you use too low an octane & get detonation, you can screw your motor royally as noted above...

GS450 -> recommends 89, I use 93 because it's not that much of a difference here (big diff is betwen regular and the others)...

[redliner1973]

I have got to say, Nick is right on this one, for the modified bikes, yes, higher octane may be what it needs, but if your stock motor is just that-stock, 87 is all you need. If you have pinging issues on 87, there is another problem such as carbon build up, mal-adjusted valves or something like that. Higher octane gas is more resistant to start burning, and in alot of cases, with a stock 'GS compression, will not effectively start burning untill the piston is at or past TDC. this solves the 'ping', and may give the false impression that it 'runs better'. This is due to the fact that when an engine pings, it tries to force the piston back down the opposite way of rotation. this lowers power, of course. when you stop the pinging, you restore that power. I believe this is why one poster on here said his bike actually ran better on 87 that 92. Ideally, an engine should use the lowest octane that it can without detonation. Higher compression engines, of course, offset the slower buring properties of high octane by it's higher compression. This brings the fuel properties to the point that it propagates combustion 'sooner'. and even higher compression will limit the 92's fuel properties and the cycle repeats.
Use of an octane rationg higher than needed can actually increase the deposit of carbon due to it's 'slower' burn properties. This in turn loweres actual combustion temps, causing the carbon build up. over time, this will cause the engine to require a higher octane fuel due to the carbon build-up induced higher compression. Alot of people who run high octane gas for long periods of time in an engine will sometimes find thier machine suddenly pings or detonates when they fill up with 87. :twisted: