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Gasoline Grade/Octane ?


Catbird

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I have a new R1200RT with less than 1K miles on it and have used only 'high test' gasoline, as specified in the owner's manual. Now that gas prices have skyrocketed, I am curious whether any of you have tried 'mid grade' or even 'regular' in their R1200RT. What were the results?

 

In my '96 R1100RT (now sold), I would occasionally use 'mid grade' with no discernable negative effects. I did try 'regular' once and experienced spark knock (pinging) on hard acceleration, so never used it again.

 

This question is driven more by my curiosity from a mechanical viewpoint than an attempt to save a few pennies (not that there's anything wrong with that!) smile.gif

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You should be even better able to experiment on the 1200 that the 1100 as the 1200 now has knock sensors. I can't speak to the 12RT but on the 12GS (essentially the same engine) I have had no issues with any grade I pour in it. Try going lower. If it doesn't knock I'd say you will be fine.

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But, if the engine reduces timing(knock sensors) to compensate, you'll likely loose gas-mileage, negating any savings. At least that's my experience with cars/trucks.

 

The 12's compression ratio is very high, making octane rather important. I'm sure with todays electronics it will run just fine with lower octane. Is it worth 50 cents a tank full to experiment?

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Paul Mihalka

I don't think using lower octane gas will worsen gas mileage. Knocking would try to happen only at wide open throttle and probably low rpm. That is when the knock sensor/timing retard would activate. That is a rare ocurrence in normal riding.

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You get the best milage with the lowest octane that your engine can use with out pinging/detonation. In all but full throttle conditions, the engine will be very happy and more efficent with a lower octane just as Paul said.

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Not surprised. There is slightly more energy in lower octane fuel. If you use enough throttle to cause a ping, the system drops to a lower octane mode. This is a reduced ignition timing, and possibly richer mixture. Most systems(as I understand them) don't just fall out of this mode when you let off the throttle. This leaves you stuck in the lower performing, lower efficiency mode until the system eases back into the default state of tune. If you putt around all day with the lower octane fuel then it probably works better. That’s not the way I ride smile.gif

 

I remember reading stories from a hand full of drag racers that tried regular and high-test in their Hayabusas at the strip. They got better ET's with regular gas. Suzuki calls for regular in the Hayabusa. I run the manufacture spec gas in my bikes, because there really isn't any point in experimenting. Any potential savings isn't worth the time it takes to calculate the mileage.

 

Disclaimer: I have no internal knowledge of the software that runs our engines. I'm basing my guesses on different pieces of information I've read over the years and personal experimenting with cars/trucks. Feel free to ignore everything I’ve said. smile.gif

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It is my understanding, however I might be wrong, that as pinging is detected, timing is retarded to just enough to stop the pinging, mixture is not increased, the timing advances to the standard setting as pinging is decreased as in a lower throttle setting or in a higher octane. The motronic wants to keep the timing advanced and only retards the timing enough to stop the pinging at any given time. As you can see, running a lower octane can have benifits.

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The knock sensors will retard timing when knock is detected and will try to re-advance the timing until knock is detected again. So there will be some minor knock here or there as it keeps approaching the limit.

 

One thing to remember is that these sensors are not perfect, nor are they simple. Quite complex. And it's difficult to get them setup to not false yet accurately detect knock. I don't know who's setup they use. But I did work on this detection quite a bit.

 

I can't speak for the RT, but the GS calls for mid-grade fuel, 90 octane (95 RON, 90 via the US R+M/2 method). It takes ~5gal to fill, the difference between the grades is almost always .10/gal. .50 per tank, $1 if you were going to go for low test instead of high-test.

 

My opinion, I think your faith in knock detection is misplaced. Rely on it for bad gas, not for day-to-day riding. And given the real money saved is so small, it's a false savings IMHO.

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Oh, the other thing that I'd add is the knock events we're talking about are NOT audible to your ears. People say "I can't hear it knock" and from what I've worked on that's just not good data.

 

Part of the challenge of the sensors is filtering out all the other engine noise. Looking for knock only during parts of an engine's rotation, learning the background noise to set a good threshold.

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I recently saw a news blurb where the talking head was trying to partially explain the high/rising cost of gas. There was a graphic on a map showing areas of the U.S. shaded differently for type of fuel used in that area. There are "17" different blends of fuel being produced and used in different areas of the U.S.

Now I wonder if this has anything to do with some bikes running great, and others running like crap. dopeslap.gif

Can't find the map now,will keep looking.

 

Mike

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Just as a follow-up to my own post...

 

After using high-test (93 octane) exclusively in my R1200RT for the first 1K miles, I decided to fill up yesterday with regular (87 octane). FWIW, I had approx. 1 gallon of h-t left in the tank. It may be too soon to make any judgements, however in the 10-12 mile ride home from the gas station, I noticed absolutely no difference at all. Unless I discern negative performance, decreased gas mileage and/or 'pinging', I'm going to continue with regular for a while.

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I have from day 1 used regular 87 octane in the RT.

No problems at all.

The only time I heard any kind of engine knock was when I was riding 2 up and didnt give it enough revs to pull away in first gear. Pretty much close to stalling out. Unless you severly lug the engine, I dont think you will notice any difference.

 

From what I remember, low octane fuel really burns faster than higher octane fuel. The octane was added to stop

early detonation in high compression engines, slowing down the burn rate.

 

I run regular in all my bikes and cars too. So far so good.

 

Rich

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