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[harleycharlie1992]

watch out most (almost all) high octane gas is leaded, VERY hard on o2 sensors, will wreck them in a heartbeat. you've been warned

[dayne66]

watch out most (almost all) high octane gas is leaded, VERY hard on o2 sensors, will wreck them in a heartbeat. you've been warned

Good to know...I last used it on a carbed '06.

[Cvostu]

I think I miss my US Keds.   Now that I am thinking back. 

[grc]

Just asking , why does the moco sell little bottles of octane booster that claim to increase octane by 3 # and help the engine run cooler?

Harley sells all sorts of crap that isn't needed or truly beneficial (except to their bottom line, of course).  They are no different than the auto parts stores or gas station mini-marts that sell that same stuff, it's all about the money.  They also sell $15 spark plugs when the $3 stock versions work just fine.  And btw, when you check all the really fine print, when all those booster products claim to increase octane by X points, that doesn't mean if X = 3 that when you add it to an 87 octane fuel it then becomes a 90 octane fuel.  Those points they mention are tenths.

I took your original question to mean you were looking at those racing fuels some stations sell that are rated at 100 to 130 octane.  If you have a stock bike that requires that sort of fuel to eliminate pinging, you have some kind of huge problem going on in that engine that you need to get fixed ASAP.  And as previously noted, most of those fuels are not street legal and they will destroy your sensors and catalyst if still so equipped.  They also won't add any power, just like those booster products don't. 


Jerry

[michaelbmenaker]

Harley lists the late model 110's at 9.15 : 1 compression (static).  The early models were listed at 9.3 : 1.  I assume the difference is probably due to a running change to the head gasket thickness I seem to remember.


Jerry

Compression adds heat. With compression this low, wouldn't higher than 91-92 octane be just wasted? Come on engineers, I know you know the answer.

[2smoke]

watch out most (almost all) high octane gas is leaded, VERY hard on o2 sensors, will wreck them in a heartbeat. you've been warned

This baffles me.  Where in the US can you pull up to a pump and buy leaded gas that is not specifically sold for "off road racing only".  There are many blends of high octane unleaded gas sold today.  We buy 112 octane unleaded and cut it 60/40 with 91 octane pump gas for our dirt bikes.  Unless you have something very old (pre-1976) you would never even consider running anything with lead.

[grc]

Compression adds heat. With compression this low, wouldn't higher than 91-92 octane be just wasted? Come on engineers, I know you know the answer.

Octane requirements for various engines are determined by a lot more than just static compression ratio's.  For instance, there are plenty of other engines on the market running 10:1 or higher static compression ratio's on 87 octane fuel.  Here's a partial list of the many things that affect the octane requirements of an engine:

-cylinder head design
-bore size
-operating temperatures
-cam timing (affects dynamic compression ratio and pressure)
-air/fuel ratio's
-ignition timing curves
-humidity
-intake air temperatures
-engine speed and load (detonation is more likely at lower speeds and higher loads)
-engine condition (deposits, hot spots in the combustion chamber, etc.)
etc.

In theory, when a manufacturer determines the octane requirement for their vehicles they test under varying conditions representative of what the vehicles could be expected to see in the real world.  So under ideal conditions, you should expect to be able to run satisfactorily with slightly less octane than they recommend, and under severe conditions you might expect to see slight detonation (or in the case of vehicles with good engine management systems you might notice a slight drop in performance as the system compensates automatically by retarding ignition for instance).  I don't count Harley's system as being one of the really good ones, since you still get obvious ping even when the ECM retards spark to try to control it.  The best automotive systems are almost unnoticeable in operation.

Anyhow, back to the subject.  Excess octane, above and beyond what the engine actually requires, serves no useful purpose.  Putting 91 octane in a vehicle designed to run on 87 octane won't make the vehicle run any better, and will in fact usually degrade performance and economy.  Don't take my word for it, there are plenty of SAE papers and other studies doubters can look up at the library or online.  So someone running a stock engine in a Harley with a 91 octane requirement will NOT get any real benefit from paying $10 or more per gallon for some 110 octane racing fuel.   

Oh, btw, when referencing octane and comparing products, you need to note the difference in rating methods and which one applies to the product in question.  Regular motor fuels sold in the USA are required to be labeled with the [(R+M) / 2] method (the average of the Research number and the Motor number).  But racing fuels may be rated with just the Research number, which is higher.  To give you an idea, the 92 octane (R+M/2) stuff at your local gas station is approximately 97 octane on the old Research number scale.


Jerry

[harleycharlie1992]

This baffles me.  Where in the US can you pull up to a pump and buy leaded gas that is not specifically sold for "off road racing only".  There are many blends of high octane unleaded gas sold today.  We buy 112 octane unleaded and cut it 60/40 with 91 octane pump gas for our dirt bikes.  Unless you have something very old (pre-1976) you would never even consider running anything with lead.

anything out of a pump will be unleaded, but a lot of this high octane fuel comes in 5 gal cans now and people put it in their newer bikes that have 02 sensors. I dont know where you live, but not in cali, there is no pump gas higher than 91, anywhere, (except the airport!! and its leaded!)