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Octane Question
- Thread starter collesidis
- Start date
marcopolo
Active member
Well, given that the manual is translated from the original German, I don't think the words "super unleaded" are that meaningful. As Paul Glaves said earlier in this thread, it's the numbers that count. The number is quite clearly 89 AKI, so until BMW says that their manual is in error, 89 AKI is fine with me. And, as for saving pennies, I couldn't care less.
36654
New member
Did you ever Google "octane BTU"?
AKsuited
New member
Another source of info
From here: http://www.cycleworld.com/2012/12/21/bmws-all-new-water-cooled-boxer-tech-preview#page-3
Fuel requirement is 95 RON/91 R+M/2.
91, not 89!
Harry
From here: http://www.cycleworld.com/2012/12/21/bmws-all-new-water-cooled-boxer-tech-preview#page-3
Fuel requirement is 95 RON/91 R+M/2.
91, not 89!
Harry
Thanks for quoting Cycle World's horribly and incorrectly written formula.
AKsuited
New member
They wrote 95 RON/91 R+M/2. It is obvious that it is either 95 RON or 91 AKI R+M/2: a reading comprehension issue rather than a math error.
This gets back to an obvious error in the BMW owner's manuals. It says "Super unleaded...89 AKI."
Well, this makes no sense - Super unleaded is not 89 AKI, 91 AKI is. So if there is an obvious error, then it is certainly open to debate. And from my previous post, Super unleaded is defined as 91 AKI.
Harry
Last edited:
Maybe in the southern tier of NY, but not all of us live there.
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johnesherman
New member
Since Anti Knock Index ("AKI") could be 89- or 91-AKI fuel use; as a result, how many BMW RT wet head riders have experienced engine knocking at the top RPM using 89-AKI fuel? Maybe BMW has improved the engine design over years that lowers the need for more anti knock fuel to reduce knock; e.g., water cooling engine head hot spots causing premature fuel burn and resulting knock?
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patm
Member
Super unleaded is a marketing thing. I believe the confusion comes from the fact that most fuel stations in Europe carry Super Unleaded 95 RON. Lower octane gasoline is not common. 95 Super Unleaded is what we would call regular fuel. The Premium fuel would be the 98 RON or 100 RON as the VPower in this pic. Sometimes it is called Super Plus.
Now is the conversion 89 AKI as in the BMW manual or 91 as in the charts I've read before, I don't know. I just know that the local gas stations have Ethanol free 91 or 93 Premium and that is what I use.
Now go ride. Winter is over.
AKsuited
New member
There would be no discussion had the owner's manual stated "Mid-grade unleaded...89 AKI," but it did not.
Harry
I certainly don't mean to belittle Alan Coles, but a number of you seem to be following his sources thinking this is scientific truth, and it's not. That, or you're sticking to the labeling (marketing) of the fuel names you find at your local gas stations and that just holds no water. The thing that BMW recommends is in the number, not the name, so let's look into that.
There is only one place in the the Chevron PDF that Alan quoted that even attempts to quantify MON or RON and that is here:
Notice it's stated as just a "rule of thumb", not a determined scientific fact. I'm sure this published document by Chevron underwent the scrutiny of number of employed engineers if not scientists before being approved for publication. I'm not so sure bout the solitary engineer he talked to at Shell.
Seems Alan takes these sources as absolute fact to conclude that RON 95 = AKI 91, and then quotes it over and over, and over.
He has supplied a couple of other sources as well. I am not easily convinced that the pencilgeek's table(s) are anymore scientific as the reference to them is no longer active on the internet.
Alan also references the following Octane article on Wikipedia, but fails to give due credit to what is says about MON, so here it is:
Wikipedia is no scientific publication either, and a citation for it's accuracy is clearly missing, so let's play along and do the math ourselves with Wikipedia's reference.
Here is the formula with proper parenthetical inclusion:
Let's start with the most liberal octane for MON = 8 octane below RON
So,... that's as if the fuel in the MON test had the MOST octane in it.
Let's do the math as if the MON were conservative, or 12 octane below RON.
And what does this tell me? It tells me that BMW is being conservative and most likely has taken the WORST case testing into account, where the MON testing had the least octane rating below RON. That makes 89 AKI its acceptable, no recommended octane rating for this wethead engine.
IMHO, they made no mistake at all. They have scientists and engineers on staff who I trust have tested this engine with a number of fuels over a number of running hours, broken the engine down and inspected it for damage, and have declared the correct fuel for it.
There is only one place in the the Chevron PDF that Alan quoted that even attempts to quantify MON or RON and that is here:
What octane grade gasoline should I use in my vehicle?
For starters, use a gasoline with the AKI or RON recommended in your owner’s manual.
(A rule of thumb is that the RON of a gasoline equals the AKI + 5.)
For starters, use a gasoline with the AKI or RON recommended in your owner’s manual.
(A rule of thumb is that the RON of a gasoline equals the AKI + 5.)
Notice it's stated as just a "rule of thumb", not a determined scientific fact. I'm sure this published document by Chevron underwent the scrutiny of number of employed engineers if not scientists before being approved for publication. I'm not so sure bout the solitary engineer he talked to at Shell.
Seems Alan takes these sources as absolute fact to conclude that RON 95 = AKI 91, and then quotes it over and over, and over.
He has supplied a couple of other sources as well. I am not easily convinced that the pencilgeek's table(s) are anymore scientific as the reference to them is no longer active on the internet.
Alan also references the following Octane article on Wikipedia, but fails to give due credit to what is says about MON, so here it is:
Motor Octane Number (MON)[edit]
Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.[1] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON. Pump gasoline specifications typically require both a minimum RON and a minimum MON.[citation needed]
Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.[1] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON. Pump gasoline specifications typically require both a minimum RON and a minimum MON.[citation needed]
Wikipedia is no scientific publication either, and a citation for it's accuracy is clearly missing, so let's play along and do the math ourselves with Wikipedia's reference.
Here is the formula with proper parenthetical inclusion:
AKI = (RON + MON)/2
Let's start with the most liberal octane for MON = 8 octane below RON
(95 + (95-8))/2 = (95 + 87)/2 = 182/2 = 91 AKI
So,... that's as if the fuel in the MON test had the MOST octane in it.
Let's do the math as if the MON were conservative, or 12 octane below RON.
(95 + (95-12))/2 = (95+ 83)/2 = 178/2 = 89 AKI
And what does this tell me? It tells me that BMW is being conservative and most likely has taken the WORST case testing into account, where the MON testing had the least octane rating below RON. That makes 89 AKI its acceptable, no recommended octane rating for this wethead engine.
IMHO, they made no mistake at all. They have scientists and engineers on staff who I trust have tested this engine with a number of fuels over a number of running hours, broken the engine down and inspected it for damage, and have declared the correct fuel for it.
kioolt
New member
Do wetheads have knock sensors to retard the timing to stop knocking?
chewbacca
New member
This thread has become the new oil thread. Some of the replies are downright stupid. Why is it Americans in general are mathematically impaired??? Let some marketing bozo call something Super, Hyper, Fantastic and some people blank out everything else. The BMW standard is 89 AKI, period. Read the frickin' numbers. As for the guy who thinks Super Duper 9x gives them better power and mileage, the science doesn't support your premise. Last but not least, don't look up the btu of octane. Most gas is 2,2,4 trimethyl pentane or a similar isomer. Guys, you are beating this dead horse to death. To the smart guys, fill 'er up with mid grade and ride on with a smile. To those who have ta run premium, filler 'er up with premium and ride on in ignorance. Ignorance is bliss, right? If you can get E-0 89 AKI, God bless you. I would buy it if I could find it. E-0 regular, I would leave alone, might buy E-0 premium though.
36654
New member
alancoles
Dress for fall & avoid it
No offense or concern taken here Rainman, but, we do see this differently.
I would point out that I don't believe I every suggested that I was providing any "scientific" evidence aside from the Engineer's statement. If I did, I didn't mean to. The closest I think I got to that would be referencing my conversation a while ago with a Shell petroleum engineer. Having done a split Biology/Geology major in university many years ago and taken both organic and inorganic chemistry, etc., I can assure you that anyone with a degree as a petroleum engineer from an accredited university is a scientist and that is who my source was for that conversation. Having said that, I stick to my previous contention that you don't need a scientific degree to figure this out (unless a scientific answer were required).
I do believe that many are missing a very important point. When trying to identify what might/should be a correct interpretation of something that has inaccuracies in it (the BMW material I referenced), it is extremely common, but completely inappropriate to only focus on that which supports one position and ignore parts which are contrary to that position.
I have tried to make absolutely certain that I have not done that, and, specifically identified that BMW does identify a name - Super unleaded and 2 numbers 95-RON and 89-AKI for my RTW. Also, as I point out earlier, for the new HP4 Race, BMW specifies "Superplus unleaded petrol, minimum octane number 98 (RON)". In Canada, at least, anything referred to as superplus, supreme+, etc., is 93-AKI not 91. By logical extension, that would put 95-RON at 91-AKI. As has been pointed out, there isn't a direct mathmatical link from RON to AKI without MON. That is because RON only measures octane under low severity engine operation (at a steady 600 rpm in a single cylinder engine and the compression ratio is increased until detonation occurs). MON measures it under more severe conditions but still in too controlled a state. AKI was brought in to give a slightly better reflection of real-world performance in road vehicles.
My 2015 BMW RT Riders Manual reads:
In that text, BMW identify 3 parameters which are not consistant with one another.
As far as arriving at a "reasonable" idea of what BMW meant to say, this is really simple stuff. As simple as grade-school math where when you have the values of 2 angles of a triangle the 3rd angle is obvious.
The same goes here. No need to get into working with math or hypothesising what might be within acceptable variations.
There are precious few good examples available to show, so I showed what I could find quickly, but the far more important fact is that while the naming of gas grades varies significantly, there are very real consistancies that do align.
In NA and Europe unleaded 91-AKI is traditionally identified as Super, or Premium, unleaded (not 100% but, I don't know maybe 85%-90% it was consistant enough that I never fixated on it). Every fuel pump I've noticed on either continent that had 98-RON referred to it a SuperPremium or some other such name not just Super or Premium, but always with an additional adjative. BMW also refers to 98-RON as Superplus, not Super.
In Canada, Esso (Mobil in the US) use the following:
The actual rule-of-thumb for RON to AKI conversions is 4-6, but, again, it can be most commonly seen as being referenced as being either 4 or 5 and very rarely as 6. Part of the problem is that the actual spread between RON and AKI is greatest at high RON numbers and least at low RON numbers, but in the mid-range of most public vehicle gas, 95-RON and 93-RON, it is close to 4.
That is precisely why I asked the Shell Engineer on three (3) seperate occassions in the conversation, what the 95-RON would equate to in AKI with their gas, and as stated, his reply was that Shell 95-RON is 91-AKI.
As I said, when you use all of these factors, the naming conventions, etc., and try to lineup the RON to AKI, the chart from pencilgeek is the one that fits all parameters best. Is it scientific proof? Absolutely not. Does common-sense suggest that it is correct? Yes.
This is from Petro-Canada:
Again, by extension that should mean 93-RON = 89-AKI, and 95-RON = 91-AKI.
Another gas companies material stating this. And all 3 gas companies I've referenced use consistant terminology that aligns with the table I provided.
The reality is that it isn't easy to parse this stuff out for some reason, but it really shouldn't matter, if Shell, Esso and Petro-Canada (actual gas companies) information isn't going to sway someone and they are willing to do some gymnastics to twist and/or ignore conflicting BMW material which has likely been translated from German into English, than they've already made their mind up and no amount of credible information will change that.
azgman
Addicted to curves
Amen, brother!
