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What Octane do you recommend

  • Thread starter Thread starter Anonymous
  • Start date Start date
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Anonymous

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Hello,

My 81 GS650G's manual said to use between 85-95. Well thats a big range. I just got my bike and have been runing 93. What has been your experiences with diffferent octanes.

Brian
 
I use 87 in the winter and 89 in the summer If it is up around 100 deg i will use 91
 
I always use 87 unleaded, regardless of brand, regardless of weather. In my 17th season of GS ownership, I've found that if it doesn't run well on cheap unleaded, the fault lies somewhere else.

Nick
 
all of you run 87, really?

hmmn...since i've had my two GS's i've put only 92 or 93 octane in them. we have 10% ethanol here in Illinois, not that it matters for the octane level really...but i figured high compression engines like the higher octane.

~Adam
 
Octane ratings vary over the country, in some places 85 is the lowest. Since octane rating relates to the flash point of fuel, use a level that corresponds to you type of riding conditions. For a stock machine never ridden hard above 90F, the lowest level is probably OK. If you have modifications and run hard, I would use the highest available. Higher octane= a higher flast point, which means detonation will only occur at much higher engine temps. I have always rationalized that since I use less gas in the bike, I always run premium. Good Luck, Ed.
 
All the G models are shaft drive, and none have the same engines as the E-models, so that rules out your having a 16 valve, high-compression engine. Those engines require the higher octane because of their higher compression ratios.

Yours does not.

Presuming your engine is not modified to increase the compression, and is not carboned-up, (which increases compression,) try it on the 87 octane.

87 Octane is what it was designed to run on, so try it and if you find it runs well, there is no reason to use high octane, except to throw away money buying a higher-priced product that delivers no additional value.
 
Suzibago does great on her steady diet of 87 octane. Anything higher would be a simple waste of money.
 
I run unleaded 98 all the time, lowest octance I've seen around here is 93.
 
There are different octane ratings given depending on the country (RON etc etc), so we may not be talking the same numbers.

Octane is tested in a single cylinder octane test engine. The MON is a measure of the gasoline's ability to resist knock under sever operating conditions. MON affects high speed, part throttle and performance (under load such as in passing). The RON on the other hand, is a measure of gasoline's ability to resist knock under less sever conditions. RON affects low to medium speed knock and engine run-on (dieseling). For a given AKI, RON is typically 8-10 points higher than the MON. As an example, 87 AKI (pump octane) fuel would have a MON of 82 and a RON of 92.

In Australia we quote in RON. Standard is 92 RON, I use 96 RON or above in the GS as it runs a lot better, and gets better mileage on higher octane than normal octane.
 
Run the lowest octane that you can and still have the engine not knock, rattle, or ping while under normal operating conditions. Experiment. If you get knocking while under normal acceleration you need to go to the next octane level. You should have some knocking if you lug the engine (like wide open acceleration while the engine is in low RPMs) but not under normal acceleration.

Nick is correct in that if you are running 87 octane and you have excessive knocking there is something else wrong but sometimes getting that something else corrected can wait and you just use a higher octane in the mean time. An example would be excessive carbon in the combustion chamber. Until you remove the head and clean it, you could have knocking on 87 octane but it would be ok to run a higher octane until you get a chance to correct it.

What ever you do, do not run the engine with a lot of knocking and pinging...you could end up with holes in the piston and under severe circumstances even a bent rod.


Hap
 
my bike ran fine on 87 octane gas till I put the suzuki 1mm oversized pistons in during a top end overhaul, it now is only happy with 93 and sounds like a old Mack truck If I try running 87.

my voyager 1300 runs just fine on 87.
 
focus frenzy said:
my bike ran fine on 87 octane gas till I put the suzuki 1mm oversized pistons in during a top end overhaul, it now is only happy with 93 and sounds like a old Mack truck If I try running 87.
Click to expand...

Any overbore keeping the stock headgasket and same piston configuration will see an increase in the compression ratio...thus the need for higher octane. Now about that pesky shaft drive... :wink:

Hap
 
Yes, sometime the increased compression from an oversize piston will require the next grade up in fuel. Fuel quality can also vary, so a try a few different types.
 
As I understood it, the theory of compression and octane is roughly point of compression vs octane number. Loosely said, 10 to 1 compression would run 100 octane, 11 to 1 run 110, 9 to 1 is ok for 90 octane, etc. The higher the octane , the slower (so to speak) the burn, preventing pre-ignition and so on . Whereas high octane on a lower compression engine may in theory give less power because the burn is slower.
 
Jon Kramilius said:
As I understood it, the theory of compression and octane is roughly point of compression vs octane number. Loosely said, 10 to 1 compression would run 100 octane, 11 to 1 run 110, 9 to 1 is ok for 90 octane, etc. The higher the octane , the slower (so to speak) the burn, preventing pre-ignition and so on . Whereas high octane on a lower compression engine may in theory give less power because the burn is slower.
Click to expand...

Many stock bikes built today are running 12:1 or greater compression ratios. Octane depends on many factors, such as compression, plug heat range, ignition timing, cam timing, and piston/combustion chamber design to name a few. Corresponding octane to compression might have been accurate back in the '70s but with the introduction of new cylinder head designs (our TSCC heads actually led the way in this area) in the early 80's changed the rules.

You are correct in saying that you could actually lose power going with a high-octane gas in a low compression engine. High-octane gas has lower BTU output per volume compared to low octane gas.

Hap
 
Hap Call said:
Jon Kramilius said:
As I understood it, the theory of compression and octane is roughly point of compression vs octane number. Loosely said, 10 to 1 compression would run 100 octane, 11 to 1 run 110, 9 to 1 is ok for 90 octane, etc. The higher the octane , the slower (so to speak) the burn, preventing pre-ignition and so on . Whereas high octane on a lower compression engine may in theory give less power because the burn is slower.
Click to expand...

Many stock bikes built today are running 12:1 or greater compression ratios. Octane depends on many factors, such as compression, plug heat range, ignition timing, cam timing, and piston/combustion chamber design to name a few. Corresponding octane to compression might have been accurate back in the '70s but with the introduction of new cylinder head designs (our TSCC heads actually led the way in this area) in the early 80's changed the rules.

You are correct in saying that you could actually lose power going with a high-octane gas in a low compression engine. High-octane gas has lower BTU output per volume compared to low octane gas.

Hap
Click to expand...

So I have learned a bit over the years(so I'm not crazy... totally :wink: ), and yes I did'nt factor in the other variables required, Chamber design, ignition advance ,etc. Kinda neat how technology has made up for old school knowhow. Sure wouldn't mind sitting over a beer or 2 and shooting the breeze with ya; nice to learn from others.
 
Hap Call said:
Any overbore keeping the stock headgasket and same piston configuration will see an increase in the compression ratio...thus the need for higher octane. Now about that pesky shaft drive... :wink:

Hap
Click to expand...
I am not sure about the head gasket, the one that was on it was a fiber with fire rings type, and the one that came from suzuki with the new pistons was/is a laminated steel gasket without fire rings, I was woried it wouldnt seal but it is holding fine.
 
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