Octane

[Elliot Cannon]

A few questions about my new (to me) 1975 CB750.  Regular or premium gas?  I also have access to about 50 gallons of 100 0ctane low lead aviation fuel.  Would it harm the engine if I used it in the Honda?  The Owners manual talks about using 86 pump octane and 91 research octane.  Are these 1975 references?  I guess I'll check on the pump, when I fill up for the first time today.  
           Cheers,   Elliot

[sgtslag]

If it is stock, then 86 Octane is fine.  If you can get non-oxygenated gasoline (no ethanol), that is supposedly better.  I ran 86 Octane, 10% Ethanol gasoline in my '79, and I run it in my '93 Voyager, without issue.  The Voyager Owner's Manual specifically warns against this, but I've put more than 8,000 miles on it, without issue.  I ran the 10% Ethanol gasoline through my '79 Honda for 13,000 miles, without issue, as well.

Octane rating is simply the resistance of the fuel to pre-detonation; the higher the Octane, the slower the fuel burns, but this burn speed difference is a very small measure of time, likely milliseconds, or less.  It is only an issue with higher compression engines, or in extremely cold weather conditions (this effectively lowers the Octane rating, which can lead to pre-detonation, or pinging, which can put a hole in your engine's pistons).  Higher Octane fuels do NOT run 'better' than lower Octane fuels; they do not give 'better' performance, under scientific analysis.  With the butt-dyno, however, all things are possible.  Cheers!

[shinyribs]

Im with Sarge.86 will do just fine. Lowest in my area is 87. I used a bunch of it,but noticed my bike actually runs about 15-20 degree cooler oil temp when using 93 octane. I use 93 in the dead heat of summer,87 the rest of the time. I run mostly highway and the high engine speeds really heat up/beat up the oil so I like the cooler temps. Strange,but the bike runs cooler in town vs on the highwayNot what you would expect from an air cooled engine.

[TOOLS1]

As long as it does not knock, or ping run it!
TOOLS

[Thorby]

I think it is a common misconception that higher, more expensive, octane is better for the engine but like Tools says, if your engine is not knocking or pinging then you don't need higher octane fuel.  If I want to invest into what my engine is burning, I add a bottle of fuel injector cleaner.

That reminds me... I need to try that famous Sea Foam thing next time I go to the Auto Zone....