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91 Octane, why?

11K views 24 replies 9 participants last post by  Ozburner 
#1 ·
If Kawasaki clearly states, 91 Octane required or severe engine damage will result then why:

are owners using reg/87 fuel with no issues? Furthermore, there's talk of 91 being too slow burning and potentially causing carbon build up.

So why the warning from Kawi when real world is saying otherwise?
 
#2 ·
I'm guessing your referencing the MOM.
Does it really state "damage WILL result"? That's an odd statement.

Compression ratios are a main function of what mfgs use to determine the recommended octane. The 1700 compression ratio (9.5 : 1) is a little high for 89 but not out of the ballpark.
The thing is; compression ratios aren't the only thing that affect when the fuel ignites.

The purpose of higher octanes is to prevent detonation or engine knock. Detonation WILL cause engine damage.

If your bike doesn't have engine knock using 89; then you don't need the higher octane.
At the end of the day though; it's your bike. If you feel more comfortable using 91; there is value in peace of mind and it isn't going to hurt anything.

Scott
 
#3 ·
Compression definitely isn't the only factor, ESPECIALLY today. My 12.5:1 car would be some 100LL sucking dragster in the 1960's (Well, assuming JUST the compression ratio); but it's an 87 octane 4-door econo-commuter today. Actually that's becoming more and more common. Very high compression ratios on small engines with variable ignition, valve, and fuel timing (my car has twin independent variable camshafts) tuned to run on the lower octane fuels. It does take advantage of higher octane fuel with a noticeable and dyno-readable boost in horsepower, but runs just fine at 87 and actually is more fuel efficient (likely because it just pulls so much timing).

The thing about octane ratings, similar to other ratings, isn't that "the moment 87 touches your bike it will instantly explode and your Dog will get cancer". It's that in just the right conditions, damaging detonation could occur. Those conditions could be accelerating up a hill in a hot day, pulling away from a stop sign or a light after sitting long enough for the engine to get hot, or some other situation where the engine is primed for knocking and pinging, and would need higher octane fuel to prevent that.

The 900 has the exact same 9.5:1 compression ratio and happily runs 87 all day long and that's all the manual says it needs. But it runs cooler, doesn't heat up at a stop, and probably doesn't have as much ignition advance as the 1700.

LOTS of factors can create a condition requiring high octane fuel. Ignition advance, compression, heat, engine load, the presence of carbon buildup in the engine, etc.

IMHO; use the minimum the manual recommends and not any less; but using more probably won't give you an advantage. So use at least 91. Some get along just fine with 87 in the 1700 engine, YMMV.

One thing missing from our bikes that almost every car has is an anti-knock sensor. If we had those, we wouldn't have to worry about it. When it detected any sort of knocking or pinging, it would pull timing. If, after pulling timing it still detected it, it would throw an error code. Alerting us to correct the condition causing it or use higher octane fuel. That's how it works in your car and that's why on a car, a Dyno can tell if you're running premium (inversely, higher octane means more aggressive timing so more power is made), whereas there's little difference on a bike on a dyno (assuming EVERYTHING ELSE is exactly the same. Though TUNING a bike to run higher octane fuel can definitely improve performance). Note that knocking/pinging isn't always audble to the rider and causes slow, gradual damage to engine components. As we have a lot of 1700 owners who run 87 and some who have run it for a LONG time (though, one particular case, @RACNRAY, does have a Dyno at his disposal to tune things) and nobody has reported a hole in their piston; I doubt it'll be an issue. But it's food for thought, that just because you can't hear it, doesn't mean it isn't there.
 
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#5 ·
Mine does not like 87. But I don't have loud pipes to mask the engine pinging sound. I will add 87 if I am out in the country and don't trust that they sell 93 enough, or can't get 93, but I then add 93 as soon as I get to a station that has it.
 
#9 ·
Yup it works and there it is... "use premium fuel, OR ELSE."

The side benefit of using premium grade here in canada is that generally, the refiners are only permitted to add 2% ethanol vs 10% in regular grade. Some suppliers have ZERO ethanol in their premium fuel.
 
#11 ·
After I did the big 3 mods, I have been running 87 octsne without issue. The bike seems to have additional decel pop with higher octsne fuels, due to the slower burn. Bike runs powerfully. No difference in power by using premium.
 
#17 ·
I tried 87 for a while with no real complaints.
One time under hard load in triple digit heat; I had some knocking.
I figured 89 would suit just fine and give a decent buffer even in the worst conditions.

With 89 I still have some decel pop around 2k even after adding quite a bit of fuel and 'marbling' the pair valve.

Scott
 
#15 ·
If you've turned the bike off it is NOT decel pop.
Decel pop happens when unburned fuel mixes with oxygen in the exhaust and ignites.

Pretty sure the noises you're hearing are the different bits of hot metal distributing the residual heat and expanding/contracting at different rates.

Scott
 
#14 ·
explanation from 'nuther forum:

"The popping you are hearing is not back-firing. It is a popping resonating sound generated by a lean condition on decel. When you suddenly close the throttle, the incoming air is choked off and the closed throttle also causes the bike to return to idle on the very lean idle circuit of the carb(s). However, momentum of the bike is actually "driving" the engine in a sense, and that engine is still spinning at rpm that needs far more gas than the closed throttle/carb can provide. The engine is still spinning but the incoming fuel rate is very low, until just enough builds up in the combustion chamber to "fire" on the exhaust stroke of the engine.

To know this for sure, the next time it happens, pull in the clutch and the popping will stop immediately, because the bike's momentum is not pushing the engine to spin. Don't "change the plugs" like some people suggest, its a waste of time and money. Messing with the ignition timing really won't help either, because it is still a lean fuel/air mix on decel that is the cause. Note, I said cause and not problem, because the popping is not at all damaging to the bike. So don't expect your dealer to fix the "problem" under warranty because it is not a warrantable situation. The EPA drove this more than anything else."
 
#16 ·
Otter

You seem to have all the answers and your mind made up.
Was your original question really a question or just a ruse to start a debate about octane.


Of course; you're welcome to start debates. They can be fun.
But in-genuine questions end up reducing involvement and flow of information.

Scott
 
#19 ·
no, the question was genuine. Mfg says "do it or else". Yet around the web plenty of owners are saying 87 is just fine. And some say, "don't burn premium", you'll carbon up your combustion chambers.

This bike isn't a 2-3 year commitment for me, so I'm looking for answers.

What's kind of funny is that people's behaviour on fuel is inverse to their behaviour with oil. Kawi says something like 12000km for oil changes, yet I don't think anyone will push their oil that far, but when Kawi says, "premium or else" for fuel, people are finding reasons not to.

play games with oil - damage your engine
play games with fuel - damage your engine

I've been doing my own reading along with the opinions in this thread and sharing as I go along.

If you'd like me to sit back, listen and keep my mouth shut.....

I'm 43 and busy with a family and life, I've got better things to do than start nonsense debates.
 
#20 ·
My apologies then.

Your first question "So why the warning from Kawi when real world is saying otherwise?" seemed to be about gathering info you weren't already aware of.
Later posts seemed more like you were aware of the things that are related to octane and engine knock and even some of the things that can prevent engine knock; but were more interested in why someone wouldn't follow Kaws recommendations.

It's all good; and no, wouldn't want anyone to keep their mouth shut.



Scott
 
#22 · (Edited)
I run the highest octane available which is 91-93 and it's usually the same price for 93 at one station as 91 at the other.

Out of curiosity; I did the math.

I bought my Vaquero in April and, shamefully, only have about 6,500 miles on it. (Hey, I was out of the country and generally very busy this year! And it rained like every day! Anyway...)

So in 6,500 miles assuming my average fuel economy of 42; we'll drop it down to 40 to make the math easier and be on the 'safe' side; that means I've burned 162.5 gallons of fuel this year.

Here, it's a 30 cent increase for Premium which is at or above the national average. Some places it's much lower.

That means in 6,500 miles I've spent $48.75 more than if I had bought regular. Given the average gas prices this year I've spent about $450+$48.75 in gas ($450 would be what I spent if I was buying 'regular'). It's not chump change; but it's also not significant. I spent more than that at dinner last night. So at the end of the day, while not insignificant, the price difference isn't great. Though the cost of repairs, however unlikely, related to pinging in the engine would surely eclipse that.

Just food for though; and to satisfy my own curiosity. It does add up; even if it's only a buck or two per fill-up more.

The carbon buildup caused my premium is a total myth unsubstantiated and that isn't how gas "works". Octane is merely an additive that resists detonation. The only disadvantage is cost. Some get decel popping, which isn't harmful; but awfully annoying. You won't hurt your bike running 'too high' of an octane; but you will with 'too low', which is why Kawasaki wants you to err on the high side, not the low side. Likewise, you change your oil BEFORE it needs changing; if the oil is no longer protecting; you've waited too long and additional wear is ensuing. Mileage interval recommendations are on the 'safe side' assuming a variety of riding conditions. To mitigate this, some send their oil off for used oil analysis. Some find they can go much farther than the recommended interval; some find their riding style leads them to needing to change their oil sooner!
 
#23 ·
That octane resists detonation, that I know and I know how it works. What I had assumed was that since our bikes have a closed loop management system, I took that by extension that there should be a knock sensor. Like a car. Where it really doesn't matter if the cheap stuff is being burned. Only performance suffers.

What prompted the question, really, is that in more than one place, members are talking about premium burning too cool/too slow/incomplete resulting in carbon buildup. It's a stretch but someone actually mentioned that the buildup could be so bad that you could eventually slap a valve. Almost believable. Almost. With this side, there's "I run 87 and my bike doesn't ping/knock.

What I learned from you, Roman, is that pre-ignition can be happening right under your nose, you don't have to hear it. I always thought that no audible knock is ok.

On the cost, I don't begrudge the extra cost.

So with me it was really a case of being scared by the idea of carbon buildup. I'm with this girl for the long haul. If it's no issue, I'll continue to buy the highest grade at the pump, knowing it's good for my girl. We've told each other we'll be together for a long time to come.
 
#24 ·
I run a PCV with AutoTune and I have removed the two rear baffles in each muffler. I've been running 89 for a few years now and the bike runs fine.

However, if I continue to accept the new fuel trims suggested by the AutoTune my bike will start falling on its face after the third or so new map. AutoTune continues to pull more and more fuel from my map until the bike becomes useless.

So I loaded a map from the Dynojet website and haven't accepted any new trims from AutoTune. It can adjust +/- 20% while I'm riding and that's it.
 
#25 ·
I know we have different fuel here, but I was running the lower RON fuel on my classic and playing with the EJK setting. It ran OK, but I found the higher RON fuel was smoother, particularly off the bottom where I ride it the most. It was also a little more heat sensitive with the lower RON.

I also notice the difference between fuel stations. SO I try to keep the fuel from the one type, or spot.

I have been know to be fussy, and can not stop fiddling with the bike..:laugh2:
 
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