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Author Topic: More Fun with Fuel....  (Read 1429 times)

Offline DesertDragon

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More Fun with Fuel....
« on: September 01, 2017, 11:31:06 AM »
Howdy..
After a member's thread on "real or placebo" for a fuel switch prompted a lot of conversation, it got me to try super in my bike.
I noticed some positive differences in the fuel switch for my 96 750 from Mobil regular to Mobil super...
Quicker warm up, increase in idle speed, elimination of "stumble" near redline, and an improvement in mpg was what I noticed.
Some of this can be explained, and some seems to be a mystery and/or flys in the face of "consensus" opinion.
 
Between rides, I've been doing a lot of research, and it is amazing just how much controversy there is on the regular/super topic beyond this forum.

I did learn a few things.  Read on if you're interested.

Octane rating:
One of the few things you can tell about a fuel by looking at the gas pump.
Also one of the things that is tested, that must conform with reality.
A surprise to me, is that "octane rating" is NOT equivalent to, or a measure of "octane content".. e.g. super grade with a rating of 93 does not (necessarily) mean that it contains more octane than the fuel from the next pump displaying 87. 
What it DOES mean is that the super/premium rated at 93 "acts" like it has a higher octane content when measured.
This can be due to actual octane content in the fuel, one or more of a large number of base stock combinations, additive additions, displayed components (typically ethanol / mtbe) mandated for emission purposes, or substances included for engine improvement/advertising (Techroline?)
So, the "octane" rating is really not an "octane number" at all - It is called an anti-knock index (in the fine print), because that's what it is.
Octane or "octane acting" components act to slow down the combustion process... (more push, less BANG)
It assists in prevention of premature ignition (knock) which can destroy an engine over time.
The "consensus" opinion with regards to "octane rating" therefore, is if you don't have knock from a given fuel, you don't "need" a higher rated fuel to prevent knock. 

Fuel formulation:
Although the octane index is not an octane measure, and more isn't necessarily better (unless you need it to prevent knock), the way that the fuels get to that number can be very different by fuel grade.  One of the major differences, is in the addition of alcohol (ethanol) to the fuel.
Although alcohol has less measured energy than "gasoline" (BTU/unit of measure) it will provide the fuel to which it is added a relatively higher octane rating.
Alcohol also burns hotter, absorbs water more readily, and evaporates more quickly at the same temperature than does "gasoline".

Ethanol is a very common regular unleaded additive, but NOT a universal premium fuel ingredient. 
Therefore, in addition to the higher rating, that extra 20 or 30 cents per gallon for super may be buying you more "actual" gasoline, rather than an alcohol/gasoline mix.

Engine Control:
One of the primary cited reasons that "premium fuel" is a "waste" is because modern engines have computer controlled, multi-sensor systems that monitor both external environmental conditions and internal engine performance, and then dynamically modify engine operation based on sensor input to optimize for desired programmed factors (e.g. fuel economy/performance/emissions/etc). 
These systems can also allow an engine that would otherwise "knock" itself to death, run well, or at least acceptably well, with the same grade of fuel.

Engine types:
There is a considerable difference between an air cooled and water cooled engine in terms of their operational temperature, yep - air cooled engines run much hotter.  There is also more operational variation in them, as they don't have the mitigating factor of a water jacket surrounding them.
If you look at what's available out there - Lots more water cooled engines - Their operating temperatures can be modified (kick on the radiator fan) which is something an air cooled motor can't do.

How does this relate to using a "higher grade" fuel in the CB 750, and any actual or perceived improvement in performance....
While there is some pure opinion which follows, at this point, I think the following may be factors that align with my improvement observations...

Fuel Formulation:
Since the super I used didn't have ethanol in it, but the regular grade did, my Nighthawk, without any vapor recovery capability would lose more fuel to evaporation because the ethanol more easily evaporates.  Over time, this would mean there would be less fuel left to burn.
Alcohol also "loves" to absorb water, and the resulting regular fuel solution would contain more water (and less energy per unit volume) over time.
These factors may or may not be significant, but in my case, since I go on a large number of short trips (gas tank heated up each time) over an extended period of time (weeks), even small differences will add up.  All else being equal, these factors would serve to increase measured mpg.

Engine:
My CB 750, being air cooled, and therefore running hotter, especially in my high desert, high temperature environment, has an increased need for for a slower combustion process to run optimally.  The bike is not equipped to dynamically alter any performance characteristics beyond spark advance.
As temperatures increase, equivalent performance requires improved "octane" to maintain optimum performance. 
(this appears to be generally accepted, and is used in racing prep design calculations)
With regular fuel, the bike may not be knocking, but that doesn't mean it's running ideally either.
I did find an interesting fact for recommended fuel grade for The Harley.
With a lower compression ratio than the 'Hawk, but also equipped with an air cooled engine, their minimum recommendation is 91 (super).
The manufacturer rating requirement for a fuel grade cannot possibly address all possible conditions, but in my case, based on some performance curve calculations, the recommended fuel rating is apparently not sufficient for my engine's needs.  If it were, there could be no improvement.
Improvement was obvious to me, and apparently some others, and although I agree that "runs better" is a subjective assessment likely to be impacted by "placebo bias", when a significant change is measured, it's no longer subjective.
The most obvious change in performance for me, was near redline, which tends to require more help from the fuel in prevention of pre-ignition. 
I cannot think of any other reason why just a change in fuel eliminated a stumble if the lower grade was adequate....

Still interested? 
If you are willing to gamble a small wager (~$1 - $1.50) on a tank of fuel, see if it makes a difference for you.
Whatever you can measure, I'm interested to know your results, good, bad or no difference.

On the "placebo or real" thread, I mentioned that it might be an interesting experiment to capture results.
I'm thinking that brand, grade, octane rating and additive (ethanol and/or mtbe) of the fuel and your bike type would be a good start.

One benefit of participation...
 ridn2
You need to ride to find out if there's a difference!





 

Keep the Rubber on the Bottom!

DD

Offline viffer

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Re: More Fun with Fuel....
« Reply #1 on: September 01, 2017, 12:32:42 PM »
Pretty good post. I've done this several times over the years in my VFR and seen ZERO difference. BUT ... Just for gits and shiggles I'll try it next fill up in the Nighthawk and let you know.

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Offline Captainkirk

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Re: More Fun with Fuel....
« Reply #2 on: September 01, 2017, 01:41:55 PM »
Pretty good post. I've done this several times over the years in my VFR and seen ZERO difference. BUT ... Just for gits and shiggles I'll try it next fill up in the Nighthawk and let you know.
I'm assuming your Viffer is EFI?
Measure twice, cut once

Offline viffer

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Re: More Fun with Fuel....
« Reply #3 on: September 01, 2017, 04:53:06 PM »
I'm assuming your Viffer is EFI?

yes it is...
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Offline DesertDragon

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Re: More Fun with Fuel....
« Reply #4 on: September 01, 2017, 06:55:12 PM »
Pretty good post. I've done this several times over the years in my VFR and seen ZERO difference. BUT ... Just for gits and shiggles I'll try it next fill up in the Nighthawk and let you know.
As the Captain said... EFI - Keyword there is electronic. 
Don't know specifics of the ECM (engine control module) in your VFR, but you have one, and it likely will automatically alter timing to ensure that it is doing what its designer intended. With enough data (and you already added some) my hypothesis is that the more intelligent the machine, the less benefit from a higher grade fuel, except for those that NEED it..
But - In a dinosaur, like I am proud to ride, the upgrade makes a difference (well, I've convinced myself already based on observation).
Take note before you dump some super in there, how long it takes to warm up. and how it takes off from idle when "cold" (relatively).
Compare that to the next day with super in the tank.  That's the first thing that struck me.

Enjoy the ride...
Keep the Rubber on the Bottom!

DD

Offline Larry Fine

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Re: More Fun with Fuel....
« Reply #5 on: September 01, 2017, 10:34:14 PM »
Compare that to the next day with super in the tank.

I just filled my first tank of regular Amoco as a test, but I believe it will require at least one more fill of regular to replace, rather than merely dilute, the premium I've been using.  I have been riding the NH more than long enough to notice any tactile or audible changes without them having to be abrupt ones.

In the mountains this past weekend, I used off-brands of gas due to ride leader's choices, using mid-grades because greater altitudes and cooler temperatures require lower octane.  I wasn't looking for it, but I could swear I noticed a smoothness after my first Amoco premium fill-up while returning home.

Switching to the lowest octane of the same brand should indicate whether my bike has been benefiting from premium.  If you think about it, regular gas should theoretically produce greater acceleration, as it burns faster.  I have always used premium in bikes because air-cooled engines run hotter.

Offline DesertDragon

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Re: More Fun with Fuel....
« Reply #6 on: September 02, 2017, 10:08:34 AM »
Larry, you make some good points, especially the "dilution" factor...
As far as a faster burn = more power.... Here's another take, from an optimized shooting perspective.
Different gunpowders, like gasoline grades, have different burn rates.
Very fast burning powders (like regular in your post) improves performance in a short barrel where there is a relatively short run to accelerate the projectile.
In a longer barrel, the same fast burning powder will not produce as much thrust as a slower burning powder, and although the differences would seem to be relatively minor, there are major measurable results between the two.
The reason the slower burn results in a faster projectile in a longer barrel, is that the bullet is being accelerated down the entire length of the barrel.
If the "burn" stops before the bullet exits, the gas pressure begins to lower and the remaining length of the barrel is actually serving to slow down the bullet through the remainder of its travel.
If you think about it, a gun and a motorcycle cylinder are not all that different, in regards to both being powered by a controlled explosion driving an object through a sealed space.
While the faster burn may have more initial pop - It is the total force applied over the length of the barrel (gun or cylinder) that results in power.
When you mention "smoother", and I've noticed this as well, it may well be that the bike "likes" a slower burn fuel, and rather than a quicker "pop", it is getting a longer "push"...  If the engine is taking advantage of this difference, it well could be a major component of reason I noticed a mpg increase.
It would also seem to explain why several people, myself included, noticed an idle speed increase with super.
If the same amount of fuel is delivered to the same engine and it begins running faster (increased RPM), it MUST have gained some efficiency.
I would be interested to hear an alternative explanation for this observation, but I doubt it would be one that made sense.  It's just physics.
Your comment made me think of one other fuel related item... 
When the Nighthawks were originally produced, ethanol was a much less common ingredient in regular grade fuel than it is today.
While the regular "octane rating" may be the same (~87) the addition of ethanol, which effectively increases the "octane number" may have changed the characteristics of the fuel burn rate enough that the engine is not operating effectively with the "regular/ethanol" fuel mix...
Thanks for getting me thinking... The ethanol/not difference may well be what's going on here...


Keep the Rubber on the Bottom!

DD

Offline Larry Fine

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Re: More Fun with Fuel....
« Reply #7 on: September 02, 2017, 12:16:11 PM »
Alrighty, then. Let's get technical.  nice1

I do understand the physics of engines. I've been reading about engine theory (and reality), especially in motorcycle magazines for, well, decades. (I'm 62 yrs old) I remember when Suzuki brought out the TSCC engine, which was designed to control the direction and speed of flame propagation.

I get the duration-of-burn/length of stroke analogy between a combustion chamber and a gun or rifle bore. The flame could be too fast OR too slow for for a given design, losing propulsion effort or wasting fuel. In an engine, is too much octane ever a mechanical concern, or merely a financial one?

Regardless of engine speed, the flame propagation speed is fixed; that's why ignition timing is advanced as RPMs increase. The idea is to "centralize" the best energy output to the crankshaft's throw when it's perpendicular to the bore's axis, like a bicycle's pedal being in front of it's axle, for best torque.

The higher the octane rating, the sooner we need ignition, in order for the greatest combustion pressure to be occurring when the piston, and thus the crankshaft throw, are in the position to turn the most of that pressure into torque. That means the ignition occurs while the piston is still rising.

Too soon and the piston tries to turn the engine backwards, which is knock and can do great damage. So, we know we don't want that. But, can too much octane cause any damage? What about loss of engine power? Can too little? As long as we avoid damage, we're discussing power loss and fuel wasting.

Octane ratings are supposed to tell us to what degree the speed of flame spread is chemically retarded, which is where the engine knock comes in. Knock can be caused by several factors, like advanced ignition timing, Dieseling, overheated bits (spark plug, piece of head gasket, carbon build-up, etc.), etc.

Let's stick to a properly-tuned and mechanically-sound engine, which is probably what we have been doing. We're comparing the flame propagation speed to the combustion chamber's volume increase during the power stroke only. Let's not forget fluid dynamics, the inertia, etc. of the air, the air/fuel mix, and the exhaust as they move through the engine at various RPMs.

You're suggesting that, with too fast a burn, there could be "wasted stroke" at the bottom of the power stroke, because the fuel burned too quickly. But, what if the burn is so slow that the waste occurs at the beginning of the power stroke, because the flame hasn't gotten really hot yet? Are  both scenarios equally possible?

There's the argument that more octane can or should provide greater power, and that less can or should. Methinks that there is no one-size-fits-all answer, that every engine, even two of the same model, may have differing octane requirements, but the manufacturer designs around a given specific power (HP vs displacement) design.

So, we're left with how fast should the flame spread for a given engine design, i.e., bore-vs-stroke, compression ratio, number and displacement of cylinders, etc. Let's not forget that a multi-cylinder engine is merely that many single-cylinder engines joined "at the hip." So, that means look at one cylinder's volume, right?

Does an 1800 cc six-cylinder engine require more octane than an 1800 cc two-cylinder engine, since the twin has larger individual combustion chambers, requiring a "faster" burn to fill them with fire? Do smaller combustion chambers require higher octane, or do they need "faster" flames because they can spin faster?

I've always heard that low octane causes knock, and that too much octane wastes money. Only recently have I heard about performance being the central part of the discussion. I'll let you know my latest and newest impressions after tomorrow's ride.

Well, that's all for now. Awaiting your replies.



Offline deaconblues082

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Re: More Fun with Fuel....
« Reply #8 on: September 02, 2017, 05:08:47 PM »
My boss (who is a bit loony) is an engine builder/tuner and he always recommends our customers use regular gas. His theory is, super/premium fuels, unless free of ethanol sit in the stations tanks longer because the higher price dictates less demand for them therefore there's more likely to be moisture in it and what have yous of older gas. Just wondering what you guys think.

Offline mollusc

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Re: More Fun with Fuel....
« Reply #9 on: September 02, 2017, 05:28:20 PM »
The engine in my '99 Land Rover is actually a Buick design from the 50s or 60s.  It will barely run on 87, despite the massive amounts of electronic wizardry going on with the engine management systems that attempts to compensate.
This is surprisingly not that uncommon a situation, although less common than it was a decade or so ago.  I think it's also not too uncommon for European vehicles to be designed for higher rated fuel.  Taking both of these factors into account, along with how ridiculously cheap fuel is in the US, I call BS on the idea that premium sits in the tank for any significantly longer time than regular.
Also remember that mid-grade is actually a pump-level blend of premium and standard, so any time a consumer fills up with mid-grade they are using gas from the premium storage tank.
made of meat

Offline DesertDragon

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Re: More Fun with Fuel....
« Reply #10 on: September 02, 2017, 06:25:27 PM »
Larry - Good post...
I had an 82 GS 750EZ with TSCC - I loved that bike.
As far as the fuel....
I'm trying to understand, by thinking out loud, reading replies, and reading LOTS of other stuff with varying opinions, what is going on in my engine. 
I started all of this with an expectation that changing fuel grades would result in a big NADA - The exception being the cost difference between super and regular... 
But that's not what happened.
I know how an engine works, but I liked your explanation of the combustion phase.

For most folks I would agree that regular is a better choice. 
I wouldn't consider it for my car, but then it also water cooled, has a computer controlling it, has relatively low compression and runs fine on regular.
My bike is pretty much opposite of that, and although I didn't know it, or anticipate it at the time, they way it acts with super has been better.
It warms up faster, I can take off sooner without stumbling at low RPMs, I can run it all the way through to red-line without a burble like I had before, and to boot, I got better mpg than with regular. 

Regardless of the specific reason(s) for this, something is going on. 
My rifle vs cylinder example was an attempt at a possible explanation, because something is happening. 
Maybe it's a lot of somethings.

While both the too fast and too slow fuel burn phenomena are possible, all other things being equal, something caused my rpm at idle to increase. 
You would not expect to have waste cause an improvement, and I don't see that as being likely in my engine.

Could it be possible that it's ONLY my engine... Anything is possible, but several other folks have commented with similar results so I doubt it.
That's why I thought it might be interesting to find out results from other folks experiments.

Mechanically, my bike was and is in great shape. I went through a recent major tune, and have a newly cleaned air filter.
It has like new compression, and I was getting a consistent 45 mpg until I switched to super.  Now the mpg is over 50.
That's an 11 percent increase...  Will others see this.. Maybe.. Maybe not...

I would think an inexpensive and very easy test, by grabbing the "other" pump handle would be worth the possibility of having a machine that "worked" better with the more expensive fuel.  To me, it isn't even more expensive as the fuel cost and mileage are a wash.
The difference in how the bike runs makes it worthwhile for me.  For someone else, maybe not.  Maybe it would be worse.
I don't know, but I also never claimed that everyone would notice the improvements that I did - I just suggested they try it.

Apparently, fuel and oil and tires and just about everything else on a bike are topics where strong opinions are held.
Everyone is entitled to their own opinion, but if that opinion prevents them from trying something that might be good...

Anyway, whether or not you notice a difference in the positive, negative or none at all, please do post it.
Keep the Rubber on the Bottom!

DD

Offline MrF

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Re: More Fun with Fuel....
« Reply #11 on: September 02, 2017, 08:42:40 PM »
This thread makes me wish even more I could have kept the NH when I upgraded bikes.  Nice work, DD.  Good points all around.  I'll be eagerly following the results.
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Offline Rakillia

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Re: More Fun with Fuel....
« Reply #12 on: September 02, 2017, 11:06:39 PM »
I can say I've never tried it.  Thought there was no point.  I would bet though that premium where I live would still have ethanol in it.  But for the sake of an experiment I'll try it.  I am confused about your use of the word octane.  Most of what you are describing would be accomplished by jetting.  Elevation, air temperature, anything that changes the air density will change the air/fuel ratio.  I've never heard of someone compensating for altitude changes with different octanes.  You would use different jets.  I'm curious about your bike DD.  Is it completely stock? Any jet changes or shims under the needles?  The late hawk is said to be lean from the factory.  Is the super somehow compensating for the lean A/F mix?  That would explain it.  If an engine was running lean and all of the sudden was running right you would get everything you describe.  I don't know if thats possible and you guys are diving deeper into this topic than I'm capable of.  Up until now my only thought of premium was some engines like it, some engines don't care.  Figure out what your engine likes and run that. 

Offline DesertDragon

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Re: More Fun with Fuel....
« Reply #13 on: September 03, 2017, 09:17:23 AM »
I can say I've never tried it.  Thought there was no point.  I would bet though that premium where I live would still have ethanol in it.  But for the sake of an experiment I'll try it.  I am confused about your use of the word octane.  Most of what you are describing would be accomplished by jetting.  Elevation, air temperature, anything that changes the air density will change the air/fuel ratio.  I've never heard of someone compensating for altitude changes with different octanes.  You would use different jets.  I'm curious about your bike DD.  Is it completely stock? Any jet changes or shims under the needles?  The late hawk is said to be lean from the factory.  Is the super somehow compensating for the lean A/F mix?  That would explain it.  If an engine was running lean and all of the sudden was running right you would get everything you describe.  I don't know if thats possible and you guys are diving deeper into this topic than I'm capable of.  Up until now my only thought of premium was some engines like it, some engines don't care.  Figure out what your engine likes and run that. 
You make some good points, and like you, I had never tried super either because I "knew" it wouldn't make a difference.
It was actually a guy on this forum that used it and seemed to have noticed results, so I tried it myself as an experiment.

"Octane" as used to describe a fuel rating, is actually an anti-knock index. It just happens to be one of the only easily identifiable qualifiers on fuel.  Ethanol is another, but you typically don't have a choice - Most metro areas use it ubiquitously.  I'm not sure if that also allies to super.
I live in a rural area, which doesn't have the same mandates as most cities do.
 
My bike is internally stock.  The air cleaner is stock in dimension, but a cleanable UNI which is likely breathing better than the stock paper.
That might cause the mix to be a bit leaner.. No other engine mods.  Carbs were rebuilt (gummed up from sitting - won't do THAT again) but they were reset to how they were. 
I didn't notice a difference afterwards.  I had not heard about the "lean 'Hawk"... Could be a factor. 
That might make sense if super "acts" like a "richer" fuel.  Maybe somebody can comment on that...
While perhaps the same results could be had with jet mods, there is no way I'm going to open up a "golden goose" to find out.
My scooter is running sweet, and since it "ain't broke"... 
 ridn2
I have always sought to understand things that I can't readily explain, but maybe this is one of those that prefers not to be known. 
I can live with that, and in any case, I'm happy with how the bike is running, especially my 51 mpg!

I like your last line, and that may be as close as I can get to an answer.. At least it's pragmatic.
I guess my engine "likes" super, some others like it, and still some others will find that their's don't care..

I'll be looking for your result, or not result...
 bkr3

Keep the Rubber on the Bottom!

DD

Offline Rakillia

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Re: More Fun with Fuel....
« Reply #14 on: September 03, 2017, 11:53:38 AM »
If the super is making it run richer than you could tune the carbs to run on regular. Too bad no one on this forum has an o2 sensor added anymore. There were a few members before the crash. That would be good data if they switched grades and recorded the A/F mix.  I know octane is a made up rating system to label somethings resistance to ignition. Anything flammable would have an octane rating.  A Diesel engine only uses compression to ignite the mixture which is what we try to prevent on a gas engine. Beyond that I've never thought about using octane to compensate for anything else.

Offline Larry Fine

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Re: More Fun with Fuel....
« Reply #15 on: September 03, 2017, 02:58:30 PM »
Just returned from "test ride #1". I noticed no change in apparent operation, power or otherwise.  Next test will be tank #2, which should be almost all regular.

Offline DesertDragon

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Re: More Fun with Fuel....
« Reply #16 on: September 03, 2017, 03:16:12 PM »
Lotsa "ifs", oh slayer of the rodents 
heya2

I don't know that it is running richer, but if it is, if that could be attributable to the difference in octane rating.
The consensus opinion says no, and if the engine doesn't knock, more octane or actually, a higher octane rating isn't necessary.
On premium fuel, it just seems to be running better, and is running better by the several measures I noted..

Again, not sure why that is. I do find it interesting that the more research I do, the more information I get that says don't use super.
Of course, most of these statements are made "theoretically" and with caveats.. In MOST engines... GENERALLY speaking, etc...
Like you said, If it runs better, use it -  is probably a lot more useful advice, as it is at least based on observation.

An "octane rating" is, strictly speaking, used as a measure of a fuel's ability to resist 'knock' (pre-ignition) like you said.
If you research further, it is derived from the measure of a fuel's burn characteristic when compared to a defined quantity of the combustion of a standard mixture, the result of which can be reported on several different scales.
RON (Research Octane number) and MON (Motor Octane Number) are combined and averaged ((RON+MON)/2) = AKI (Anti-knock Index)
The AKI is what you see on the pump here in the USA as (typically) 87 for regular.
If you want to read about it, Wikipedia has a pretty decent explanation:
https://en.wikipedia.org/wiki/Octane_rating
I also learned in the article that a diesel only compresses air, and not the air/fuel mixture..
I learn something new every day... 
But I digress...

Anyway, you are right, octane or octane rating doesn't compensate for anything else, other than as an assist to prevent knock.

But - The octane component of a fuel is a relatively small part, and there can be (and are) many other differences between fuel compositions among producers and distributors, as well as between fuel grades (regular / mid / super).
It may be possible (likely?) that the basic composition or specific included ingredients is making the difference. 
Again - I don't know, but something made a difference.

If you are familiar with the "placebo" effect - (some people can be cured of illness with a sugar pill) a similar thing can happen with humans interacting with machines, like a motorcycle, for instance, where the thrill of a new fuel changes their perception of how "well" the engine runs, and it suddenly runs "smoother" and has more power.  This is usually based on an expectation that the new brand is better, and then the rider "discovers" what was anticipated. 
In my case I wasn't expecting anything, so it would be like I'm about to be cured of cancer with a new drug being tested, but they tell me it's only a sugar pill... Result - No placebo effect, because I "know" it won't do anything.

Dang... Again I've managed to digress...

Anyway, at this point I've spent too much of my remaining time on this planet discussing the relative benefits of fuel, and I'll post anything that looks significant, either way....
 (sudden drop in mileage / return to long warm up / top end burble when switching back to regular / engine EXPLODES due to octane overdose)
 yaaaah3
... but at this point I'm not thinking it's worth the effort to find out, or even if that is possible regardless of the effort.
That's it - I'm goin' for a ride!
Keep the Rubber on the Bottom!

DD

Offline DesertDragon

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Re: More Fun with Fuel....
« Reply #17 on: September 07, 2017, 08:27:08 AM »
Quick update - another fill up with a tank of super, another 50 mpg..
This one included a 50 mile interstate ride @ 75 mph...
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DD

Offline Larry Fine

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Re: More Fun with Fuel....
« Reply #18 on: September 08, 2017, 04:43:09 PM »
Test ride #2: Not really an experimental ride, just normal usage: leisure rides, chores and stores, going to work, etc.

So far, I have noticed zero difference on my second tank of regular grade, though still the same brand, Amoco (is is sold exclusively at BP stations everywhere?). By the way, for those too young to remember, Amoco premium has been lead-free at least since the 1950's that I know of. (I remember it also called "white gas", supposedly suitable for lanterns, etc.)

Correction: It's always been lead-free, at least since American Oil began in 1922. From Wikipedia:
"While most oil companies were switching to leaded gasolines en masse (italics mine) during the mid-to-late 1920's, American Oil chose to continue marketing its premium-grade "Amoco-Gas" (later Amoco Super-Premium) as a lead-free gasoline by using aromatics rather than tetra-ethyl lead to increase octane levels, decades before the environmental movement of the early 1970's led to more stringent auto-emission controls which ultimately mandated the universal phase out of leaded gasoline."

I've been using the Amoco premium for decades, starting with my '73 CB750 (I'm not sure whether I was as strict with it in my '72 CL450), and also in my '82SC. Back then, at least in the '73, I noticed it made a detectable difference compared to regular (no mid back then, except Sunoco), but I didn't necessarily stick with Amoco when using regular.

So, I can not state for certain whether the grade or the brand made the difference. I can tell you that, on the Amoco premium, I rode the bike year 'round, and it was often my only vehicle (picture boots sliding through the snow and slush in winter (hey, gotta get to work, right?)), and went four-and-a-half years (yes, 4.5 years) without pulling a spark plug once.

When I did finally take them out, all four plugs were clean enough to re-install with only a re-gapping; the insulators were a light grey, the metal surround dark but with no deposits. I went ahead and replaced them because old plugs can leak, and they were already out. By the way, they were Champion plugs, which I've heard "shouldn't" be used in Japanese bikes.

My current NH750 has been the same so far. I've had the bike for somewhere around ten years or so. I changed the plugs when I got it, not knowing their age or condition, and only once since, using NGK model DPR 8EA-9 plugs I got from Advance Auto Parts, where I also get oil an oil filters. Why Advance? It's closer and cheaper than my local Honda dealer.

Again, no difference so far, and even my local, privately owned-and-operated bike shop mechanic said he recommends regular. I had been using the reasoning that an air-cooled engine runs hotter (which it does) requires a premium-grade gas (which apparently it doesn't). I will keep all y'all (plural of y'all) posted on any future developments. Ciao for now!

Offline DesertDragon

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Re: More Fun with Fuel....
« Reply #19 on: September 09, 2017, 10:08:35 AM »
Test ride #2: Not really an experimental ride, just normal usage: leisure rides, chores and stores, going to work, etc.

So far, I have noticed zero difference on my second tank of regular grade, though still the same brand, Amoco..

Again, no difference so far, and even my local, privately owned-and-operated bike shop mechanic said he recommends regular. I had been using the reasoning that an air-cooled engine runs hotter (which it does) requires a premium-grade gas (which apparently it doesn't). I will keep all y'all (plural of y'all) posted on any future developments. Ciao for now!
Interesting... So you went from Super to regular and I went from regular to Super...
I should point out that my bike still ran well on regular, but with super, quicker warm-up (cold-blooded reduction), no stumble near redline and improved mpg was what I noticed.
When you say "zero difference" I'm wondering what (or if) you are measuring...
I guess the major thing for me is the mpg...
Do you check your MPG when you fill up?
If so, what are you getting?

 
Keep the Rubber on the Bottom!

DD

Offline Larry Fine

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Re: More Fun with Fuel....
« Reply #20 on: September 09, 2017, 10:03:50 PM »
When you say "zero difference" I'm wondering what (or if) you are measuring...
I guess the major thing for me is the mpg...
Do you check your MPG when you fill up?
If so, what are you getting?

The zero difference comment means exactly that (no smart-ass attitude intended); it starts just as easily, warms up just as quickly, accelerates just as strongly during either first-gear hauling ass or top-gear roll-ons (rolls-on?). Surprise.

Honestly, the only thing I have noticed is less exhaust popping when decelerating. Maybe there's something to the faster-combustion theory, leaving less unburned vapor in the exhaust gasses to be ignited in the exhaust system.

With a varied driving manner, as well as different levels of topping the tank (whether I'm about to park or keep riding), I get nowhere close enough to the same mileage (125 to 170 miles) for a fuel-based difference to manifest itself.

Maybe my bike just happens to be tuned enough to burn any grade completely enough that there is no noticeable difference. I would probably have to subject it to a dynamometer to ascertain whether there is a difference, but I won't.

Offline sgarnett

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Re: More Fun with Fuel....
« Reply #21 on: September 10, 2017, 02:11:29 PM »
I used to compete in autocross with an LS1 Camaro. Those engines are extensively programmable. I did a lot of tuning work with a wideband lambda sensor.

The LS1 is quite efficient, and makes the most power with relatively lean mixture. However, even with a colder thermostat and aggressively programmed fans, I would get a 10-20 degree F rise during a competition run (roughly a minute). As a result, I had trouble with pinging late in the run. Retarding the spark did not help.

In the end, I had to add extra fuel as the coolant temperature rose just to quench (cool and slow) combustion. In other words, I was using excess fuel to increase the effective octane.

The stock Nighthawk tuning is reputed to be leanish anyway to meet emission requirements. I have not confirmed this yet, but it certainly is plausible for the era. E10 inherently runs a little lean in an engine without closed-loop control. I am also quite certain that the air-cooled engine temperature varies more than 20 degrees in normal operation.

Gasoline also varies not only by season and state but even by municipality. Besides ethanol content, some gasoline blends contain varying amounts of oxygenators, which may further lean the mixture. Then there's other variables like exhaust mods.

I was shocked by how much the LS1 tuning was affected just by changing the flywheel. There are no independent variables in an engine. Everything affects everything.

To me, it is entirely plausible that some carbureted bikes in some areas might run better on premium fuel, while others may not. However, I suspect that those that do run better on it would also benefit from rejetting.

Offline hppants

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Re: More Fun with Fuel....
« Reply #22 on: September 11, 2017, 07:08:54 AM »
I've heard that water cooled motorcycle engines run hotter than air-cooled.  Nearly all are now water cooled in order for them to run hot enough to meet current emission standards.  I've never been able to substantiate that, as I don't know how hot air cooled engines run.  I suppose in the absence of any air flow, they will continue to heat up until they overheat.

Can anyone fathom a guess as to what in premium fuel (higher octane rating or additive) might cause a NH engine to warm up faster (less total choke required)?  Has the idle speed (or choke rpm at comparable positions) thought to be higher?

I would think that the higher octane rating (slower rate of burn) would lead to more exhaust popping, rather than less.  With a slower rate of burn, all other things equal in the motor, one would think that the possibility of some unburnt air/fuel getting past the open exhaust valve on the exhaust stroke, where it would be ignited with the hot exhaust.

FWIW - I tried a tank full of premium in my FJR on my recent Arkansas trip.  As much as I could, I tried to duplicate conditions, even though I know I did not.  Regardless, there was no difference in fuel mileage.



Offline sgarnett

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Re: More Fun with Fuel....
« Reply #23 on: September 11, 2017, 07:58:16 AM »
I have not measured the temperature of the Nighthawk engine.

You are right that modern water-cooled engines are by design running hotter than might be optimal for the engine because it changes the mix of exhaust gasses.

However, my point was that a modern water-cooled engine is operating in a much narrower range. Regardless of ambient temperature, the engine temperature is regulated to a fairly narrow range (ignoring extreme weather conditions).

I don't know whether a Nighthawk cruising at 70mph on a 70 degree day runs hotter or cooler than a modern water-cooled bike at the same 70 and 70. However, I'm quite certain that the air-cooled engine varies through a much wider range in normal operation. Ambient temperature, speed, RPM, and throttle are all going to have more effect without a thermostat to regulate the temperature.

As to how it would affect the idle, I suspect that is more about the mixture (including offsets by ethanol and/or oxygenators) and volatility (i.e. how well the fuel is vaporized in the carburator).

Offline DesertDragon

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Re: More Fun with Fuel....
« Reply #24 on: September 11, 2017, 09:35:21 AM »
More good comments.  I did find it interesting that Larry Fine has the same year bike (96), was using super and went to regular and discovered he's been wasting money because his bike runs as well or better on regular.  In my case, I went from regular to super and found some advantages.
Some others did, and other's did not.  Some swear by super, others swear at it.

I guess the basic problem to getting an "answer" is there are too many variables, the biggest one being that all fuel is not created equal.
While octane is measured, there can be a huge difference in nearly every other aspect of a given fuel's ingredients.
In my case, I am convinced that it has a lot to do with ethanol, or that the super I'm using doesn't contain it, where the regular did...

Since this discussion is about fuel, and there is no way to effectively compare fuel chemistry (correct me if I wrong here), along with all of the other variables, e.g. temperature, humidity, atmospheric pressure, specific engine's compression, jetting, etc, etc, etc..., let alone significant differences that are possible even between two bikes of the same make and model, at the end of the day, I doubt a definitive answer is possible, beyond "if your bike likes a certain fuel, use it, and if it doesn't care, use the best price fuel you can find"..
Keep the Rubber on the Bottom!

DD

 

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