The last time I refilled the bike, I put in some 87 grade fuel, and now there's a big pinging sound coming from the engine. I checked the book, and it said to get new fuel. Here's my problem- It says I should use 91, but there's only 87, 89 and 93. WIll I be ok if I go with the 93? Also, do I need to siphon out the tank or will it be ok if I just drive around until the gas runs out again? Thanks
The general rule is to use the lowest grade that does not make it ping. One tankful of low grade should not hurt anything unless it is really bad. Then put in the highest grade. Run that for a few tankfuls and see if it improves. Then after a while, try the mid-grade. See if that works. if not, go back to the expensive stuff.
at least you are only filling 3.5 gallons of 93...thats like 5 dollars...better than 20 dollars worth of mid in a cage!
Is the pinging sound a death sign? Is it a big deal? Is it damaging the engine and something I should replace immidiately?
I believe it is just engine knocking. It is alright, it just happens with lower grades of fuel. Just put higher octane in.
Quote from: YohanIs the pinging sound a death sign? Is it a big deal? Is it damaging the engine and something I should replace immidiately?
It can damage the engine but it's a bit like a minor strain in a muscle- stops you doing something that could cause more damage if you keep doing it. Here in the Land of Oz we get 91 and 95. I found the totally stock '01 got better performance and better fuel economy with the 95 but when I rejetted for the Uni filter it ran better with the 91. I'm not sure why that is- is there a petroleum chemist in the house that could enlighten us? :)
The octane question is always an interesting one. The way I understand it, higher octane contains more burnable fuel for unit volume and thus tends to be a bit more reactive, igniting quicker and hotter...which if your engine is tuned lean (GS especially in CA) results in a litle beter power and smoother ignition...but if you've re-jetted to a richer mix then a higher octance fule will just overcompensate, result in preignition, and less efficient burning in the cylinders. A lower octane fule when you've rejetted should run smoother...so in only 1,927 tanksful of cheap-o gas, you'll pay for that re-jetting job!! Ride safe. :thumb:
Geez lookit all those tipoz..typoes...TYPOS!!! Rough day. sorry. :)
The higher a fuels octane rating, the higher its resistance to detonation (ie less burnable). Running a higer octane than nessecary won't hurt, but is a waste of $ more often than not.
The pinging sound you hear with too low of an octane (or several other causes) is the air fuel mixture in the cylinder head exploding around the perimeter of the piston crown. It shouldn't ever explode at all really, it should burn and NEVER explode. The more the mixture is compressed however, the more it wants to burn and the first part to get compressed is around the edge of the piston/head. Without enough resistance to burning (octane) that outter band can explode instead of being burned with the normal combustion event.
As bikes get on in years and start "acting their age" they can start needing a different octane rating. Carbon buildup on the piston and cylinder head changes ever so slightly the shape of the combustion chamber and can raise the compression ratio just a tad. It can also make the process of moving the end gasses away from the edge of the piston more difficult and the next thing you know, the bike is "pinging" or detonating on the same grade of gas you have been using for years.
OK... Lots of misconceptions about fuels and octane here.
Let's see if I can make sense of it for you.
Octane is an anti-detonant. Detonation is when the fuel/air mixture is compressed and ignites on its own without the aid of a spark from the ignition system. When normal combustion occurs, the speed of the fuel/air mixture ignited by the spark plug is in the neighborhood of 5000 feet per second (fps). If the fuel has too low of an octane rating, the compression of it and the air during the upward stroke of the piston (during the compression stroke) can be enough to ignite itself without the spark from the spark plug. When this detonation occurs, the flame front travels at something like 20,000 fps. Since the piston is still on the way up in the compression stroke, this "explosion" tries to push the piston back down. This is where you get the pinging/knocking sound. IT IS DETRIMENTAL to your engine, it is not okay. Something mechanical will eventually give up and in a big way ie bent/broken connecting rods, pistons, cranks etc...
The reason engines knock is because the octane grade of fuel is too low (not enough anti-detonant) for the compression ratio of the engine. Compression ratio is the ratio between how much volume is in the cylinder with the piston at Bottom dead center and how much volume is left when the piston is at Top dead center. Most modern engines have low enough compression ratios to be able to use lower grade octane fuel without pinging. I don't know what the ratio for the GS is, but it's probably in the neighborhood of between 8 to 1 and 10 to 1. The higher compression ratio of 10 to 1 would require a higher grade of fuel to prevent detonation since you're compressing the mixture more than at 8 to 1.
I often use 100 octane aircraft fuel in my stock GS engine. I assure you it doesn't give any extra power, none! (I use it because I can get it free). The reason I don't get any extra power is because I have not changed my engine's compression ratio. If I were to install different pistons and shave the cyl. head to make the combustion chamber have less volume with the piston at TDC, that would raise my compression ratio, and then I would have to run high octane all the time to prevent the fuel/air mixture from detonating. With a higher compression ratio, I can get more power out of that same fuel/air mixture.
I'll sometimes hear airport friends that use the 100 octane in their cars, stock engines, no modif. and it's funny to hear them say things like "Yah Man! I ran some 100 octane the other day and my car had so much power!" I then proceed to ask them about engine modifications (there's usually nothing except for a K&N filter) and when I try to explain them that the fuel didn't do anything for them, they get all pissed off.
There's obviously more to fuel than what I've written, but this should give you a good primer on the subject and remove some of your misconceptions about high/low grade octane fuels.
Quotehigher octane contains more burnable fuel for unit volume and thus tends to be a bit more reactive, igniting quicker and hotter
This is incorrect, fuel is all made from the same stuff, Petrol. Where the difference in power comes in is with the engine compression ratio. A high compression ratio engine produces more power, if you're able to ignite the fuel at the proper time. And that's done by additives in the fuel to raise the octane (anti-detonant) value of the fuel. Lead is one such additive that keeps everything burning normally when under high pressures.
:cheers:
My understanding is that the reason older engines may need higher octane fuel, is because as the engine wears, it can get rough spots (pits, bumps, ridges, etc.). Since these are not smooth, they act like little sort-of radiators: they heat-up faster, and the cool-off faster (give-off their heat faster). So when the new (cooler) fuel/air mixture rushes-in, it meets these "hot spots" which give-up their heat a little faster, and the spots can act like diesel glow plugs (that is, perform the function of a spark plug, without the spark, just heat). Moving to a higher octane gas means the gas resists premature detination better, and waits for the spark to blow-up.
But, as mentioned, higher octane does nothing unless the engine compression and possible ignition sources are causing pre-ignition (aka "pinging").
Oh, one other thing: I have mixed gas before when I drove a gas-guzzler, to try to find the magic octane (e.g. 10 gal. 93 octane, 10 gal. 90 octane). This isn't too much of a pain if you're paying the pump, and have a few minutes to kill. But it would seem pretty pointless to go to that much trouble for a bike, which is already pretty efficient (1 gal. 93, 2 gal. 89 octane? Is the time worth the $0.40 savings?).
My CA 02 GS actually drives a little stronger with 87 octane verses the 93 stuff :?
Quote from: JohNLAMy CA 02 GS actually drives a little stronger with 87 octane verses the 93 stuff :?
This is because, as wingbolt said, higher (and unecessary) octane means its less prone to ignite. So if you run a crazy high octane on a low compression motor... your just hindering performance.
Good post wingbolt.. i was going to say most of that, but you covered it better then i would have.
Rashad,
Thanks for the compliment. I tried to keep the post as short as possible, but it is somewhat of a complicated topic.
BTW, I got the #4 washers and they'll go out tomorrow. Still waiting on the pilot jets.
Quote from: wingboltRashad,
Thanks for the compliment. I tried to keep the post as short as possible, but it is somewhat of a complicated topic.
BTW, I got the #4 washers and they'll go out tomorrow. Still waiting on the pilot jets.
Hey, thanks a lot once again! I can tell im very very lean in the low end, because the idle hangs like mad! It wont go down until i play with the clutch..
Hmmm, I think I got it:
1. All gasolines, regardless of octane ratings, have about the same potential amount of energy per gallon.
2. No, octane is NOT a measure of a fuel's power, but of resistance to ignition from HEAT.
3. Under identical combustion chamber conditions, a higher octane fuel will burn slower.
4. "knocking" or "pinging" is the result of fuel igniting as a result of the heat of compression BEFORE the spark plug fires. Uncorrected, this will eventually damage the engine starting with the pistons.
5. Engines with higher compression ratios can create higher combustion chamber pressure and higher heat. Under these conditions fuel is burned more efficiently, and increased octane ratings allow extraction of more of the potential energy in the fuel. (how much more? I don't know.)
6. Finally (phew!!) there is no reason to use a higher octane fuel than your engine requires, (in most low to medium compression ratio engines this means regular grade) unless you own stock in Exxon/Mobil. Pinging and knocking are symptoms that something may be wrong with the compression/combustion process, such as timing, spark-plug problems,
internal damage, etc. Bumping up the octane rating may take care of things for a while.
100-octane airplane fule?? Sounds like stuff I used to drink back in college.
Ride safe. :thumb: