For those that advocate using 87 octane in these bikes

[UncleMike]

I used to work as a line tech in a GM garage. For years when the weather got cold suddenly in the fall, we would get a slew of Grand Ams come in on the hook ( tow truck) It turns out EVERY one of them , the owners were putting in 'hi octane' gas. On the Grand Ams with higher mileage and poorly maintainenance, the resistance to ignition of the wrong gas resulted in FLOODING AND NO STARTS HAHHA. Insidethe garage ,when the car warmed up, it would always start!!! the higher the octane, the more RESISTANT to ignition. it's the compression ratio of your engine that determines octane requirements, it is not that "hi octane" puts out more power or "runs better ". people at the pump are simply uneductated and the gas companies don't help , why hell... they want YOU to waste money.

Mine was one of them.

[tkent02]

people at the pump are simply uneductated and the gas companies don't help , why hell... they want YOU to waste money.

This is all there is to it.

[Normk]

The term "3/4 race" doesn't make much sense but then neither does any other description of camshafts excepting as specifically related to one application. There used to be a continual drone by the uneducated who would blather on about lift and duration, overlap and such but it all means nothing as anyone who has had extensive experience with actual camshaft comparisons in the real world.

No one can list off two camshaft specifications and then detail the differences in engine operation in a way that is useful. I know some will get their hackles up over this point but it is so. The OEM manufacturers design and then are forced to run extensive tests with the camshaft in the identical engine configuration intended in order to determine how it will really perform. Camshaft companies such as Crane, Isky, etc. do the same thing which is why they list the intended application with some precision as any significant change in engine influencing factors can throw the whole equation out of balance.

Combustion, gas flow dynamics, etc. are much better understood today than in the 1970's and 1980's then our GS engines were designed but talking to industry insiders will likely still reveal the same cautions.

Here's an example from the real world:

We (1970's) fitted several log salvage boats having a different hull configuration with Ford 351 Windsor marine engines and experienced a new issue at wide open throttle & full RPM. The engines would "pop back" in the intake, which is an indication of some factor causing ignition of the air fuel mixture in the intake. This is always a condition of joy as there is little which is more fun than dragging tools and parts to a boat slip and doing major surgery while the owner is chaffing to get going.

Through the list of likely causes and came up dry....hmmm, what now? Talking to Barry Shadbolt who operated Shadbolt Cams who were a camshaft grinding shop in Vancouver, he offered that they had experienced this issue due to a camshaft grind change so dialed up the camshafts supplied in these engines and found a small difference in lobe timing configuration....OK, what now?

Since Ford were apparently now using this new grind (which worked well in other applications) we determined what another grind would be the best option in search for a solution so accepted Barry's suggestion of several grinds onto Ford blanks which we then installed and tried in series. I recall vividly the early Dodge Duster 340 grind profile which was solved the "popping back" issue because it dropped fuel consumption from 17 gallons per hour (which was quite good for that application) to 11 gallons per hour and pulled about 1,000 RPM more on the same prop! The 17 to 11 difference was manifest completely on a propellor change.

When sharing the information, I divided the resposes into two groups: those who were intrigued and accepted the information with interest; and those who "knew all about it". I never bothered talking with the second people again as they were obviously completely a waste of space. Many other examples....

As someone very ably posted earlier, the compression ratio is only one of the factors influencing the octane rating (resistance of the fuel to detonation as compared with octane gas) of the fuel required. Combustion chamber design, charge density, air/fuel ratio, combustion chamber wall temperature, and on and on all influence required octane. Alcohols tend to have a higher octane rating than do common gasolines however there are other well known issues, compounded by the fact that we seem to find significant differences in alcohol percentages. Nice!

I also prefer to keep the alcohol percantage as low as is possible because of concerns regarding deterioration of fuel system components and lower power output (heat content) so agree with the others who have posted this consideration.

Mostly, as someone "cut to the chase" in posting, just run fuel and oil which meets or exceeds the engine's actual requirements and don't get hooked up into the "magic" of myths.

As for the "pirates" and their air cooled V-twins, if I were riding one of those .... no, can't handle that scenario..... If recommending to someone who can't be talked out of riding one of those silly things, my recommendation is to a higher octane fuel, especially for warmer weather.

Those engines have a rear cylinder poorly placed for cooling and tend to be lugged, both of which make for high combustion chamber pressures and temperatures. A higher octane fuel would seem to be indicated as a second choice to riding something with a 20th century engine design, but that's another subject.

Good thread, lots of opinions and cross checking for accuracy.

I hear ya Dan, before I went to mechanics school in 73 we called them full or 3/4 cams as well until one student used that term in class, the instructor had a fit hahaha.

[josephfrantz]

i know what smells awesome is the cotton candy scented alky additive from jp cycles. my eyes still burn when i warm my bikes up in the garage but it smerlls like the county fair. minus the manure i mean.

[SqDancerLynn1]

All you Fiat lovers? I had a X 1/9 Newer version of the 850. Called it the "Green Frog"
My GS850 had some problems with pinging Was caused by a bad intake boot

[lonerider00]

CRAP !! First you tell me not to use motorcycle oil and now I cant use car gas. Is there secret air I should be using in my tires too....

Nitrogen! an inert gas that is more stable

[Planecrazy]

I P!ss in my tank. Runs fine but if I plan on doing a lot of riding I have to drink a lot of beer.

...and if you're running at higher altitudes the beer might not be enough. You might have to use the harder stuff to get "higher" before pi$$ing in the tank!

FWIW, both my 550L and 1100G pinged and I used higher octane fuel to eliminate the problem, after carb cleans and adjustments didn't seem to help. Sounds like since Dantheman acquired the 1100 he has succeeded in taming the problem in all but more extreme conditions. My opinion is that, as with manufacturer's fuel economy claims, in this case "your mileage may vary..." Thus, the logical conclusion is that for some the 87 octane is all they'll ever need for their GS's to run perfectly, while some of us find that despite clean carbs and tuneups our GS's still "behave" better on higher octane.

I never worried about the difference in cost because I generally rode only a few thousand miles per year. However, for those of you who ride daily the difference definitely adds up.

My .02

Regards,

[bccap]

Ride More Worry Less. Good advice..........................

I use 94 from Chevron. Because it ain't got no ethanol. And lets face it. It's not exactly expensive to run a motorcycle.

[UncleMike]

Thus, the logical conclusion is that for some the 87 octane is all they'll ever need for their GS's to run perfectly, while some of us find that despite clean carbs and tuneups our GS's still "behave" better on higher octane.

Absolutely right. With bikes ~30 years old being ridden all over the world in every condition imaginable, we're all going to have different experiences.

Plus, if riding the 1150 cross country taught me anything, it's that 87 octane is very different station to station/pump to pump/etc. Just meet manufacturer requirements and find what makes your bike happiest.

[platinum2]

i dont know what the hell you guys are talking about
i have used 87-93 if im correct , and my bikes all ran better with the higher octane! fuel, low octane ,and the motors will rattle, good fuel will burn cleaner, atomize better,and get better mpg.
yes i have used it and noticed it, in street bikes and off road bikes and quads,ect...
"$hit gas is $hit-
oh and i hope no one has gas stations that water down the fuel, like our local harpers use to , my lawn mower would run on there fuel, a few different times!

[82Shafty]

i have used 87-93 if im correct , and my bikes all ran better with the higher octane! fuel, low octane ,and the motors will rattle,

I'm appauled at the IL garbage gasoline. My GS has marbeled a lot lately on 87 which I find disgusting considering it has the compression ratio of a 125hp mid 70's ford v8.

Not only my GS, but my Bonnie started pinging even on 93. Mobil and Shell.

I'd fire the bike up after a fill up, put my helmet back on, gloves back on, go to take off and marbles...WTF.

GS, yesterday, waiting at a light, go to take off somewhat aggressively, holy marbles, I actually let off of it sounded so bad.

GS, This morning, 65F, cruising at 50mph in 5th, go it hit it 1/2 throttle and it marbles, pull in the clutch, drop it down two gears and give it another go. I don't recall this bike marbeling so easily in the past. It's a liter bike, I shouldn't have to drop it down two gears at 50 mph so it won't detonate all over itself.

GS, My next attempt will be a Yamaha ring free shock treatment or spray it right into the carbs. IF that doesn't curtail the detonation after hopefully a decarboning, then I will step down in plug temp.

[7981GS]

I still for the life of me can't understand anyone being SO CHEAP as to think that an extra $.50 per tank of fuel
to run even 89 octane in your stock bike and save your engine from damage is TOO MUCH to pay???


Eric

[oldpara]

I use 89 in all of mine, seems to work fine.
The ethanol troubles me but..
I don't get into the minutia, to many variables.

[hjfisk]

I believe alot of the [marbling as it is stated] ,that we are experiencing on our bikes has to do with the ethanol that is in our fuels now. I don't believe it matters on the 87-or 93 octain as far as marbling. As far as performance I have multiple bikes and I run 87-89 in all of them and with out problems . And have done this for 30 years. The only bikes I run high octain in is the race bikes with 11.1 or higher compression. Then I run VP 100 octain .

[JEEPRUSTY]

I still for the life of me can't understand anyone being SO CHEAP as to think that an extra $.50 per tank of fuel
to run even 89 octane in your stock bike and save your engine from damage is TOO MUCH to pay???


Eric

Yeah hell I started spoiling myself to 97 and be damned if the bike does not run far better now.
What is the compression ration cut off? I think my 550 is 9.8 to 1
I doubt there is much wrong with the lower octain but there is more in premium fuel than just the price.