Octane... proof?! (or a dumb question?)

duane_sword

duane_sword

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Ok, I am Australian so that gives me an unfair intellectual disadvantage from the start.

With that as context, here goes my attempt at what I am sure is a stupid question....

I use high-octane (the highest I can get in Boston anyway which is 93-octane) fuels in my 2010 BMW E61 and also in my 1974 BMW E9 (it is modified to accept the unleaded nectar)... back in Australia I could get 95-octane and it was also available when I lived in the UK...

But I have absolutely no confidence on the quality of the fuel supply here in the USA... for all I know the local gas station has one fuel tank that feeds the same pumps with 89-Octane, 91-Octane and 93-Octane....

a) is my skepticism warranted?... or is their some agency/authority who assures Octane given the price differential

b) is there anyway to have a manual/handheld "meter" to test fuel octane?... I imagine the folks at sprint kart racing, SCCA club racing etc need to check that folks are not spiking their fuel for higher rating... my concern is that I am paying for 93-Octane and getting less.

Ok, silly questions over. Welcome the education and learning!
 
I can't answer any of your questions, only pose a new one. I have been running my coupe with US 93 octane(I hope) for over 20 years. I did this with the original engine(a euro CS spec, carbs) and then a 3.3 five series with '73 style fuel injection.

I have done nothing to "modify" either engine to accept American Weasel Piss. Never had a problem or ping or knock or anything.

Your Thoughts.

Steve
 
First off, you need to understand that the US "octane" value is calculated in a slightly different manner than the AUS "octane" value, namely AKI vs. RON. AUS used RON, USA uses AKI. AKI and RON use different methods to determine the resistance to detonation. US 91 octane is approximately equivalent to AUS 95 octane, for comparison's sake.

Anyway, as to your specific question about the vending of gasoline, most stations have two tanks, one for high octane, one for low. Mid grade is a blend between the two. Somewhere on the outside of the pump, it should have an inspection sticker stating the last time it was inspected for volume correctness and output correctness. This usually happens once a year and is run by a state/local agency. Non-compliant pumps are immediately disabled or repaired and re-tested, and the operators are fined a large sum. There are also random, unannounced checks by the same agency.

Moreover, the fuel is inspected for quality by the refinery and is subject to random inspections while on the trucks. US gas quality is pretty tightly controlled compared to some other countries due in part to the EPA.

That said, there have been times when people do exactly as you say; however, given how most cars these days have knock sensors and throw a code when poor grade gas is used, the cars actually tell you when the distributor is doing this, making it easy to alert the appropriate people.

Example:
http://www.newjerseynewsroom.com/state/14-nj-gas-stations-accused-of-selling-inferior-grade-fuel

In terms of a handheld tester, that would be extremely difficult given the testing methods. They generally involve blowing up a sample and comparing it to pure octane, something that doesn't lend itself to a handheld tester. As far as I know, they usually control the fuel source at those kinds of events, rather than police each person's fuel supply.
 
I believe from previous posts by the more knowledgable couperisti that using unleaded does not harm E9 engines. Hope so, as I have been doing so for the last 5 years. Right?
 
In my case the car runs great with 87 except that one in a few times when I shut down the engine I get dieseling for half a second or so. I filled an entire tank with 91 last week and the dieseling went away. This only works with carbs of course, and I am not sure if it is worth using higher octane to get rid of the dieseling as opposed to giving the car a sharp accelerator pedal pump before shutting it off.
 
The short answer to reducing DS's valid skepticism is to purchase fuel from a name he can trust. Some folks refer to these companies as "top tier" businesses. They have a reputation to uphold which translates into profits.

From a lay perspective, there are several layers of review for fuel sales in the Boston area. The Federal Trade Commission has jurisdiction over interstate fuel sales, and may delegate some of the testing and enforcement to each State. The Environmental Protection Agency also enforces fuel sales as it relates to all levels of production and consumption and - you guessed it, the effect of the product on pollution and health. Each State has agencies that work hand-in-glove with their Federal counterparts.

Massachusetts evidently has a Department of Environmental Protection that undertakes fuel testing. Boston has a Weights and Measures Department that typically handles - quantities. It is unclear that this body also tests for octane, but in many States, Counties and Cities similarly named "Weights and Measures" Departments are charged with so doing.

In addition to Government monitoring and enforcement, the oil companies do their own testing to ensure that their licensed merchants are purveying the real stuff. As one might imagine, if their reputations were in jeopardy, this might harm sales. Likewise, car manufacturers have a vested interest in ensuring that their vehicles get the fuel they were designed to consume. If Porsches started performing poorly in the Northeast region, Porsche would want to ensure that its reputation remained intact. Lastly, consumers themselves have a "limited" voice both in their pocketbook and by word of mouth when their valuable and beloved family member develops a cough or a ping.

If you want to do your own octane testing, there are several means available. First, run tankfuls of each rating and make your own seat of the pants determination. Next, you can become a chemist and make your own chemical measurements with samples obtained at the pump (but this hardly vitiates the possibility of a switch which could happen virtually anywhere) Third, obtain an infrared octane analyzer and give it a whirl.

http://www.ftc.gov/os/comments/fuelratingnprm/100514tesoropresentation.pdf

http://www.chevronwithtechron.com/products/documents/69083_MotorGas_Tech_Review.pdf

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bill said:
I believe from previous posts by the more knowledgable couperisti that using unleaded does not harm E9 engines. Hope so, as I have been doing so for the last 5 years. Right?
Click to expand...

Hardened valve seat material typically installed in softer aluminum alloy cylinder heads made the addition of lead-based lubrication virtually unnecessary. You and the rest of us are in ok-shape. Anecdotally, there are several postings about the need for fuel additives and unleaded fuels, but few if any postings about valve seat wear/recession in the M30 caused by using unleaded fuels?

The problem of unleaded fuels was a concern for those with non-hardened valve seats. This occurred mostly with engines using cast iron heads (Detroit plants) pre-'72 (When the US began transition to unleaded fuels and when many engine manufactures began reducing compression ratios). The transition to unleaded fuels was also a major concern for those with high compression engines (mostly pre-'72). Lead also had the benefit of increasing octane ratings, its removal from most pump gas did the opposite. :confused::shock::cry: A few companies marketed higher octane pump fuel without the use of tetraethyl lead, well before the government enforced transition, but the operative word is a "few" and that was a long time ago in a galaxy far far away. One such example:

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http://e9coupe.com/forum/showthread.php?t=6627

http://www.chevronwithtechron.com/products/documents/69083_MotorGas_Tech_Review.pdf (P. 93 - not definitive, but slightly informative)
 
Top Tier

BMW (as well as a few others) endorses Top Tier gasolines. I believe it's due to better detergents in the gasoline. Google this & you can get the list. In my area (Phila suburbs) it's Shell, Texaco, & Exxon.
 
I had thought that the only reliable means of octane testing was to run it through an extremely expensive "test engine" presumably manufactured to exacting tolerances, which had a variable compression ratio. The point at which a given fuel produced a knock was the determination of its octane rating.

Now it appears there are other means? Recall that gasoline is a complex mixture of hydrocarbons, and knowing just which ones are present, and at what relative amounts, does not determine octane.

I better go look up those links, but I've been running 87 octane forever (20 or so years) and not had any issues with it. Maybe I just don't know what a good running engine is supposed to run like.

FWIW, the motorcycle shop I go to has five gallon cans of race gas for sale. I didn't ask how much or what the octane rating might be.

There's an huge online FAQ that goes into exhaustive detail about gasoline, what's in it, what octane is and how it's measured, and what you can do in your own backyard to modify the octane rating of whatever liquid you put in your tank. You have to have a lot of time on your hands, but for we of engineer inclinations, it can be found here: http://www.faqs.org/faqs/autos/gasoline-faq/part1/
 
The "gold standard" for octane testing is, as you describe, a test engine. (See page 6 of attached link. http://www.ftc.gov/os/comments/fuelratingnprm/100514tesoropresentation.pdf ) Science marches on and per the article, alternative octane testing is available, testing results are correlated with the "gold standard" results, and it has therefore gained limited acceptance.

I express no opinion as which is preferable other than to observe that more portable equipment (with scientifically established accuracy rates and quick response times) fosters more testing of more samples and thus more protection for ex pat Aussie consumers.




Some of us still use time-tested mercury-based thermometers. ;-) Others rely on thermal strips and electronic apparatus.:?

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The depth of knowledge on this forum is great!

Thank you. Knowledge is power (literally if the octane is good!).

I have found my nearest Shell station and will be fueling all three of my BMWs that span nearly 40 years of the roundel with "V-Power 93".
 
Avgas is about 130 octane as far as im aware - my old cars run really well on it!
 
umm, avgas is not necessarily 130 octane, unless it's sold as such. Many light planes can run mogas, which is the same stuff we put in the tank each week or so. IIRC one needs a certification to do so, but it's certainly not uncommon.

Avgas around here is about $6 a gallon and I don't recall that it's 130 octane. Why would one need that much knock resistance? Answer: without reallyreally high compression ratio, or an engine that's been majorly boosted, you wouldn't. But if available (and legal) go to it. I don't think it's legal to use it on-road.

Some would say if you don't get caught, it's okay. My opinion is different.
 
As it was explained to me Avgas is 100LL - 100 being the octane but thats MON not RON andf when you convert it its like 130 RON.

Ariplanes with car engines and Rotax can run mogas but put it in your big six conti and it wont like it one bit!

I know my old 107sl goes a lot better on it and the de catted 840 also likes it a lot.
 
yes, for engines with knock sensors which were quite unavailable back in the day. Unless you count your own pair of ears, of course.
 
I wouldn't trust any fuel that was stated to be 130 octane. I don't know if that is even achievable. My race car engine has a compression ratio at around 14.7:1 and I use 110 or 112 or a blend of the two depending on temperature and the track I am running. I have not seen race fuel rated higher than 116. That by no means says higher than 116 does not exist but I still would not believe 130.
 
Gwittman - i was using an opinion given to me but a quick google seems to suggest that it is more like 100 octane in a road fuel sense, from Shell's website:

Road fuels tend to be measured on a RON scale, for which unleaded fuels tend to be 95 - 98 RON but are only 85 - 87 MON. Avgas is measured on Lean Mixture (similar to MON) but also has a Rich Mixture Octane rating.

The Lean Mixture rating is 100 octane (15 octane higher than the comparable 85 MON for unleaded Mogas) but Avgas also has a Rich Mixture rating of 130 which allows higher supercharger boost pressures to be used without detonation occurring. This is particularly a problem when using high power settings at low altitude, for example during take off.

As you can see TEL in Avgas makes a significant difference to the octane rating and without it Octane ratings would be back down to 80 - 85 Lean Mixture - the level for road fuels - instead of 100 / 130. This is not a problem for most typical modern normally aspirated engines as their compression ratios are quite modest and detonation would not be a problem with 80 - 85 Lean Mixture Octane fuel.
 
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