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Same ole octane question

5K views 23 replies 5 participants last post by  redfish 
#1 ·
I generally follow the OEM owner and service manual recommendations, but noticed a lot of 1500 owners regularly use 87 octane which is below the 90 minimum for the 1500 engine.

I tried 87 and the engine runs fine even in hot weather - no pinging that I can hear. In fact, I notice a little better gas mileage using 87 and I think it may even have a little more power, but that could be just my imagination.

But, I'm still a little concerned since the manual states severe engine damage can occur using a lower octane. Could there be any long term consequences using the lower octane?
 
#2 · (Edited)
Japanese and Europeans use the RON (Research Octane Number) to come up with their octane rating. In the states, we use the RON and the Motor Octane Number, or MON, add the two and divide by two. Thus, a 91 RON will be an 87 RON+MON/2. Look at the gas pump and you'll see either RON+MON/2 in parentheses, or AKI, the Anti-Knock Index, which is the same thing.

I looked in my owner's manual and it said 91 minimum octane RON. Which means 87 here is just fine.

I use to run premium in the bike, and it ran a bit sluggish and got lower mileage. I didn't understand all this octane stuff at first, and like most consumers, assumed that higher octane gas was "the good stuff", had more power and so on because of oil company marketing. But in reality, octane rating is simply the point at which fuel ignites under pressure and how quickly it burns. For high compression engines, like racing engines or some higher end passenger cars, a lower octane could result in the fuel pre-igniting under compression, causing pre-detonation, which can destroy an engine. Thus, higher octane was introduced to retard detonation. That's all it does. Otherwise, the gas is pretty much the same. But if your engine is a lower compression engine, the premium may not burn as quickly and can (but not always) cause some carbon buildup and reduce mileage.

Best to follow the manual. If your manual says 91 octane RON best use it. If not, you're wasting money for no added benefit.

FWIW, some guys swear by premium fuel with no ethanol in it, but ethanol serves basically the same function as octane. That is, it burns at a lower temperature and is slower to ignite under compression than straight gasoline, and does not burn as quickly. But in my bike, 87 octane with ethanol still seems to be more efficient than premium 91.
 
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#4 ·
Japanese and Europeans use the RON (Research Octane Number) to come up with their octane rating. In the states, we use the RON and the Motor Octane Number, or MON, add the two and divide by two. Thus, a 91 RON will be an 87 RON+MON/2. Look at the gas pump and you'll see either RON+MON/2 in parentheses, or AKI, the Anti-Knock Index, which is the same thing.

I looked in my owner's manual and it said 91 minimum octane RON. Which means 87 here is just fine.
Thank you PatC.

My 1500 is an 02 Drifter and no paper owner's manual was available. The generic online PDF Owner's Manual for 1500 Drifters states the AKI, or RON+MON/2 minimum rating is 90. It lists the RON minimum rating is 95.

That's my concern and reason for confusion. Apparently some 1500 models and years have different minimum octane ratings. Yours list a lower minimum. I was under the impression most 1500 engines and years had the same compression ratio of 9.0:1. I guess not.
 
#3 · (Edited)
Pat's got it. There doesn't seem to be a rhyme or reason, but some Vulcan models list RON, and some R+M/2. My 900 listed 91RON, which is equivalent to 87 R+M/2. The Vaquero listen 91 R+M/2 as minimum!

Run at least what the manufacturer recommends. Running higher won't hurt anything but also won't provide any benefit unless engine timing is manipulated to take advantage of it.

Also; because this always comes up in Octane threads; compression is not the only metric anymore. Both the VN900 and VN1700 platforms have identical compression ratios but the VN1700 requires 91 R+M/2 and the 900 87. Likely the 1700 needs the higher octane due to higher combustion temps that can occur at some points, such as aggressive riding or riding in traffic (Where the engine gets warm). My car has a 12.5:1 compression ratio and thanks to variable valve timing, anti-knock sensors that electronically adjust ignition and other such technologies it can run just fine all day lone on 87. Because the engine adjusts itself, on a Dyno, there are significant gains running a higher octane fuel. Some might look at those results as evidence that more octane = more power. But the reality is, it's the engine, not the octane. On our bikes, there won't be meaningful gains unless we adjust timing. On cars that do adjust timing automatically (most modern cars), higher octane fuel will provide a boost in power.

Octane is a resistance to detonation. Period. Not cleaner, not more powerful, not anything else. The aforementioned performance gains come because cars can advance timing and take advantage of longer burns without detonation. Timing being equal, power will be equal.

As for Ethanol, it's not evil. It won't corrode your parts. E10 is not the same as E85, which is harmful. If you remember back in chemistry class, you remember that things in different quantities in solution have different properties. Sodium and Chlorine are both toxic, caustic, and will kill you. Together they form sodium chloride which you need to live, and probably put too much of all over your food! (Table salt). But mixed in a slightly different way and you get some of the gasses that were used to kill troops in WWI. E10 won't harm your engine. It will absorb more water than straight gas, and does have less potential energy than straight gas; so it's not without it's caveats. But it won't hurt anything. All fuel, E10 or otherwise, should be stored properly when not used for any extended length of time (whether stored in a can or stored in a bike over the winter).
 
#6 ·
Pat's got it. There doesn't seem to be a rhyme or reason, but some Vulcan models list RON, and some R+M/2. My 900 listed 91RON, which is equivalent to 87 R+M/2. The Vaquero listen 91 R+M/2 as minimum!
Thanks Romans. I've read quite a bit on the subject here on the forum, and I'd like to think all 1500s are the same, but apparently not.

On the ethanol, E10 is pretty much everywhere now and I understand E15 was to be, and may still be phased in at some point. (I think E15 and E85 are the same mixture) My 08 truck is "Flex fuel" approved for up to E15, but my outboard motor sure isn't.

I still don't get any "pinging" using 87 in the 1500 Drifter, but maybe the pipes are so loud I couldn't hear it anyway.
 
#9 ·
All very good info. Thanks so much. Based on what you've said I started buying 87 (with ethanol). After 3 tanks I am now getting 2 mph better. I also noted it seemed to be running better. No knocks. Yesterday, I opened her up and she runs 112 now. On 92 or 93 she topped out at 105. The only confounders is an oil change and new air filter. As the old one wasn't visibly dirty, I don't think the filter plays. Wind and elevation and incline aren't variables either..., very intriguing.
 
#13 · (Edited)
Octane ratings are a minimum. So go up, not down. Though check your manual to see if it says "91RON", because if it does, that's equivalent to the 87 R+M/2 you have on your pumps. So you'd be safe to go with that.

Otherwise, generally speaking, use at least what the manufacturer recommends and no lower. Plenty go lower without problems, if you want to, go for it. But that's, at least, what the manufacturer is saying when they give you a minimum recommendation.

My bike asks for 91 R+M/2, and I frequently run 93. Often times, actually, 91 is made by mixing 93 octane fuel with 89 or 87. It's not uncommon for gas stations to have two tanks; 87 and 93, and mix various ratios to produce 87, 89, 91. Whereas the other station down the road might have the same 93, pumped straight, for the same price. (This is according to a family friend who is a general manager for a gas station chain. In her case, they get 87 and 93 delivered, sell 87 and 93, and have a mixing pump that makes 91 and 89.)
 
#16 ·
Cool. then you should be good to go with regular gas. :)
 
#18 ·
#19 ·
In the United States, the anti knock rating is expressed as "Ron + Mon / 2". Also "AKI" or anti knock index; all the same thing.

In Japan and other countries, they use simply RON.

So if your manual says 91RON, that's equivalent to 87 R+M/2. So you can use as low as 87 at the pump.

If it says 91AKI or 91 R+M/2, then that means you need to use at least 91 at the pump.
 
#20 ·
Ok, sorry guys. Romans and PatC seem to be contradicting each other. Maybe I'm adding to the confusion, so let's start over again...forget Japan and Europe.

I live in Ohio, USA. My 2002 , 1500FI says 91 R+M/2. My choices at the pump are 87, 89, or 93. My question is 89, or 93?

Thanks
 
#23 · (Edited)
Run what you want. My manual says same as yours, and I've been running 87 for years and I get a bit better mileage and throttle response, with no problems. If you're running 93, you're just burning money. :D

http://www.nicoclub.com/archives/gasoline-octane-myths.html

A good read that puts it in plain Engish.
 
#21 ·
We're saying the same thing.

Run 93. The manual lists a minimum. So run at least that. If 93 is what's available, run that.
 
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