which gas?

[Pat Kelly]

Reminicing back to my days at an automotive tech school (AZ Automotive Institute) in the late 70's, I recall a demonstration.
The subject was octane. The instructor had a long, clear tube. 3-4 feet long and 2 inch diameter (or close to that). He put a few drops of low octane gas in the tube and rolled a ball back and forth inside to distribute the gas. Removed the ball (don't want a projectile do we? Or do we? ). He lit the low end of the tube and you could watch the flame front travel from one end to the other. He repeated with high octane gas and the flame front moved slower. Higher octane gas burns slower.
The conclusion that was forced into our heads was that the higher octane wold work better in a small-displacement (small bore) engine. In a large bore cylinder the exhaust cycle may come into play before all the fuel is burned in the combustion chamber though it will continue to burn in the exhaust manifold/pipe.

[metalistik]

87 for me.

I mostly use 87 with an occasional lucas treatment. I ride my sled daily and don't get any ping pong. I think it has definitely a lot to do with your timing and carbs. If you're in sync and adjusted as a couple of the guys have said, there will be no ping.


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1979 XS1100 Special - Daily rider

[XJOK2PLAY]

I mostly use 87 with an occasional lucas treatment. I ride my sled daily and don't get any ping pong. I think it has definitely a lot to do with your timing and carbs. If you're in sync and adjusted as a couple of the guys have said, there will be no ping.


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1979 XS1100 Special - Daily rider

Same for me... no ethanol... no pings. 87.

[metalistik]

I also think that higher octane would change your carburation(or whatever the proper term is...). So if this bike is made to run on low octane, putting higher grade might actually reduce performance.

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1979 XS1100 Special - Daily rider

[cywelchjr]

I've experimented more than once with high octane gas and while it doesn't seem to affect performance the bike does seem to run hotter and gas milage goes down. This happens on both my 400 and 1100, and yes, I'm aware that I could retune for the higher octane (used to do it with my cars back in the day) but then I'd have to run the higher octane all the time, and I still probably wouldn't actually get any better milage, just (maybe) a little more power. It's just not worth it IMHO. Now on my Camaro I can run the higher octane and while the milage doesn't go up, the kick in the back of the seat does, but that's because it's got a knock sensor and will automagically take advantage of the increased octane. Of course it also runs a little hotter because of the flame front hanging around in the cylinder a bit longer too.

[fredintoon]

I buy gas at my local Co-op because I get a 4 cents a litre dividend on it.
And I buy 87 Octane gas because I have never noticed any difference in performance the odd time I have tried filling up with 89 or 91 Octane gas.
Mind you, one time Mr Stupid topped up his tank from the can of 2-stroke mix and I didn't notice any performance change then either.

[petejw]

i was just noticing the octane rating of your fuels over there,
we have a higher octane fuel over here,
our standard unleaded is 92
and we have unleaded at 95 and 98.

we also have a 10% ethanol blend but i cant remember
what the octane rating is atm,
i put some in my bike the other day and it lost
performance and ran like crap, it runs well on the 92.

[Luxury]

In Australia and Europe the octane rating shown on the pump is the RON, but in Canada, the United States and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI, and often written on pumps as (R+M)/2). It may also sometimes be called the Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. There is an 8 to 10 point difference between RON and MON, so the octane rating shown in the United States is 4 to 5 points lower than the rating shown in Australia for the same fuel.

That said, I've noticed a difference running fuel with ethanol, even with the same octane number.

[perurider]

After reading this thread, the next time I put it on reserve and got gas, put in93 octane(Marathon), filled up, now its hard starting, after its running I notice no difference, except maybe less MPG. So, 87 is what i'll use.

[XSive Okie]

I run 87 in my bike, 4-wheeler, lawn mowers, and all my cars and trucks, but living where I do in Oklahoma, still have the option to avoid ethanol. Eth makes all my rides run like $hit, and fuel mileage goes downhill.

[roadrider]

'79f

I pulled the right side cover and it is printed on there to run 91 in the bike . I tryed the lower grades and lost mileage, power and it seamed to run hotter. In Montana you can get 91 without the ethanol, Thats the best reason for me.

[Crazcnuk]

That '91' under your sidecover was referring to late 70's gas ratings.

The calculation is done differently now so the current 87 is actually the same or higher than 92 was back then.

[barrelguy]

Gas

Finally noticed the big red light on my dash telling me to put something in the tank. Closest was a Mohawk so I filled up with 87. Then I noticed that this stuff contains "1% ethanol". Didn't think much about that but I have noticed that I could have fed the old girl chilli and beer considering all the farting going on out the back end. Next time I think I'll push it a block to a real gas station.

[barrelguy]

That should read 10% ethanol, not 1%

[cywelchjr]

That should read 10% ethanol, not 1%

And unless there is something wrong with the beast these things handle the 10% just fine. It will lean the mixture out some, and if you have both in the area I would stick with one or the other, but they will run either. Frankly if richened up for the ethanol, it will actually run a little cooler since at proper mixture it runs slightly cooler. But you WILL get lower mileage. Unfortunately, many if not most of us south of the border no longer have a choice between ethanol gas or virgin stuff.