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10-02-2008 10:59 AM #1
BMW explains using lower Octane gasoline
Straight from the BMW spokesperson, we get the final verdict regarding using 89 or 87 octane gas in our 91 preferred cars.
Running On Regular: Do Premium Vehicles Really Need Premium Gasoline?
From Stan Baldwin online
Long before gasoline rocketed through $4 a gallon many people were dismayed to see a significant percentage of their income disappearing into the tank of their car. Today, a wobbly economic outlook, increases in the cost of most other forms of energy, as well as the cost of life’s staples, have prompted folks to look for every possible way to cut back on spending. “Can I save money by running my car on Regular?” “Will it hurt the engine?” my friends ask. More than one person driving a car the manufacturer has spec’d for Premium has told me “I use Regular and my car runs fine.” Are there consequences of “down grading” your fuel? It is definitely a timely question, so we sent e-mail inquiries off to a half dozen manufacturers asking about their technology and their policy on the matter.
While waiting for their reply let’s review some internal combustion engine characteristics. Fuel does not truly explode in a cylinder, at least it isn’t supposed to. It burns smoothly, albeit very rapidly, across the cylinder. The octane rating is a measure of the propensity a given fuel has to burning, rather than exploding. Gasoline “exploding” in the cylinder is frequently called “detonation” or more colloquially, “knocking” or “pinging”. These explosions, because they happen as the piston is rising during the compression stroke and try to shove the piston back down the bore, can do damage over time. In the case of severely stressed motors, such as in race cars, a few seconds of serious detonation can destroy the engine. Two of the mechanical considerations affecting how smoothly a fuel burns are compression and cylinder head configuration. Two variable considerations of great importance are the temperature in the cylinder and the ignition timing. Every manufacturer designs and builds their engines to operate most efficiently for the application intended with a gasoline of a particular octane rating.
Not all that long ago, before the advent of engine management systems, the result of tanking up a high compression vehicle with standard grade fuel was immediately obvious. Providing the stereo wasn’t cranked up past 100 decibels, the pinging or knocking from the engine compartment let you know something was not right. Driving up a hill, towing a load or simply accelerating quickly produced an unnerving rattle from under the hood. It sounded very much like your carbureted V-8 had morphed into a diesel. Until the age of microprocessors enabled the creation of engine management systems, the consequence of a steady diet of low octane fuel could be fatal for a high performance engine.
General Motors, Honda, Toyota and BMW responded to our inquiry. Honda’s public relations representative declined to comment on the issue. Toyota noted that essentially all their current models are designed to run on 87 octane. I asked about using 85 octane, available in some markets, and Bill Kwong of Toyota corporate PR told me they would run fine, with maybe only a slight 2-3 percent decline in horsepower and fuel mileage. But 85 octane is usually only offered in markets at altitude (i.e. Denver, Colorado) where the reduced oxygen doesn’t allow an engine to reach full designed power in any event. If you drive a modern Toyota, the octane rating of your fuel isn’t much of an issue. But what about a brand aimed squarely at the performance market? What about BMW?
Thomas Plucinsky, BMW Product and Technology Communications Manager told us all BMW engines are designed to run on 91 octane. All performance testing, including EPA emissions and fuel mileage, is done with 91 octane. However, though BMW is all about performance, their motors will run on 89 or 87 octane without damage. The knock sensors pull the ignition timing back and eliminate detonation. There will be a loss of power and a decrease in fuel mileage, but the size of the horsepower loss and the increase in fuel consumption depends upon many factors, such as ambient temperature, exact formulation of the fuel and driving technique, so BMW does not offer any estimates for operation on lower grade fuels. One not so obvious concern, Mr. Plucinsky noted, is the type and quality of additives the gasoline companies include in the fuel. Premium gasolines may have better additive packages which are more effective keeping fuel systems (particularly injectors) clean and working efficiently, than those in regular grade fuels or off-brand products. Using lower octane or off-brand fuel could be degrading the fuel system over time, setting you up for a repair bill down the line.
Dave Muscaro, Director of Engine Development/Calibration for GM power trains explained GM has “three flavors” of fuel specification for their offerings: Regular (87 octane) Recommended, Premium (91) Recommended, and Premium Required. Again, we are more concerned with the last two categories where regular could be substituted for the specified Premium. All the engines have a knock sensing ability that retards the spark when detonation occurs. For the premium recommended vehicles the spark advance will be pulled back enough to eliminate the detected knocking. The typical driver will not notice a performance decrease, except under load, and mileage will decline slightly. The engines intended for performance, such as the LS7 or the supercharged small block V-8, are Premium Required powertrains. The customers clearly were not primarily concerned with economy when they chose a performance vehicle and GM optimizes the engine management system to deliver the highest possible power output at all times. To this end the detonation control system does not retard the spark to the point required to prevent all knocking. It would seem a determined deranged drag racer could run Regular in his Corvette and, over time, he might manage to melt a piston or two.
If burning 87 octane in your car, when 91 octane is specified, will not harm the engine, and the performance degradation is not noticeable in typical driving, how much money can you save? The Energy Information Administration, U.S. Government Department of Energy, offers some figures for US gasoline retail prices (these are averages, all areas, all formulations). A year ago Regular was going for $2.982 a gallon and Premium was commanding $3.196 a gallon. The 21.4 cent difference delivered a 6.7 percent saving over Premium. This June 23, 2008, Regular extracted $4.079 from your wallet while Premium sucked up $4.312 for every gallon. The differential (23.3 cents) has grown slightly since 2007 but buying Regular is now only 5.4 percent cheaper than Premium. Since 5 percent is roughly the typical percentage of mileage decrease to be expected with the 87 octane fuel in a 91 octane engine, is there any savings at all?
Bottom Line: Most modern engines are fuel injected and controlled by sophisticated engine management systems which can rapidly and accurately compensate for lower octane fuel by retarding the ignition. Running these cars on 87 octane will not hurt them. However, the immediate savings at the pump may be wiped out by the subsequent drop in fuel mileage and performance, not to mention the possibility of damage over time.
10-02-2008 01:44 PM #2
Re: BMW explains using lower Octane gasoline
"There will be a loss of power and a decrease in fuel mileage, but the size of the horsepower loss and the increase in fuel consumption depends upon many factors, such as ambient temperature, exact formulation of the fuel and driving technique, so BMW does not offer any estimates for operation on lower grade fuels."
Buried in some promo literature for my BMW R1200RT motorcycle, there is the figure of 101 peak HP when running on reduced octane (87?) fuel. As the normal spec is 110 HP, that would equate to about an 8% power loss compared to premium.
10-02-2008 06:26 PM #3
10-02-2008 07:46 PM #4
I think it is making less sence to run lower
octane fuel as the prices are going up. The price difference between regular and premium has always been around twenty cents. When gasoline prices were at around $2.00 The price difference between regular and premium was 10 percent. Now that gasoline prices is at about $4.00. The price difference now is only 5 percent. Therefore, I would not run regular in my car just to save 20 cents.
11-22-2009 12:36 PM #5
12-12-2009 06:05 PM #6
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12-15-2009 02:42 PM #7
I must call [Oops!] on this
I used Costco (and sometimes Safeway) for our 525i (200K miles, still running strong when wrecked), my son uses same in his 335i, I used it in my 330xi (140K miles) and we have never had fuel-related problems. The techs at the independent we uses, which is 1/4 mile from the local Costco, also use the gas there. (All use the 92 octane, and an occaisional bottle of Techroline - BOUGHT FROM COSTCO.)
Your techs are lying to you; they can't tell. In fact, the gasoline from Costco and Safeway is, in most cases, the same gasoline as you get from Chevron, just with Techron thrown in.
12-18-2009 01:43 PM #8
Re: I must call [Oops!] on this +1
Agreed. I've used the cheapest 93 octane in two BMW cars & one motorcycle for over a decade and also have had no fuel related problems. In my area it's the inexpensive stations which have the fastest turnover as well as the best chance of finding ethanol free premium. The only problem is that they tend to be quite crowded, especially since their recent price for 93 octane is $.30 to $.40 oer gallon less than the so called "name brand" stations
01-03-2010 01:19 AM #9
01-16-2010 11:24 PM #10
detonation an "explosion"?
I took issue with his somewhat misleading characterization of detonation as an "explosion". A flame front will ignite and burn at a relatively constant rate, given a presumed combustion chamber pressure. It is an "explosion" only in the sense that it is an unintended, uncontrolled potentially destructive ignition of the still compressing fuel/air mixture as the piston rises (aptly described as the synonym "preignition") that is caused by rising compression chamber pressure on the piston upstroke on the compression cycle (normal) combined with the not so normal presence of a hot spot on a burr or sharp edge of metal in the combustion chamber or on the piston itself or a hot shard of carbon igniting the charge in advance and in place of the spark plug.
07-06-2011 02:51 PM #11
Detonation vs Preignition
Hey Doc... There is a real difference between Detonation and Pre-Ignition. Both are destructive and as you noted, different in their cause. Detonation occurs when unburned fuel is compressed and ignited causing a separate flame front to occur in the combustion chamber. When the two fronts meet there is uncontrolled ignition of any remaining fuel and an explosion occurs. We call this ping. The effect is that of hitting the top of the piston with a BIG hammer. This will even damage the piston causing a concaved indention in top. Spark plugs insulators can also crack and chip from the high frequency vibrations that occur as a side effect of the explosion.
Pre-Ignition is just as you describred it. Extreme heat in the combustion chamber usually caused by a lean condition will cause carbon or shards of metal to glow and actually ignite fuel before the intended ignition occurs, thus, Pre-Ignition. Most people don't take in consideration the refrigerant properties of Premium fuel vs lower octanes. that's a whole nuther story.
12-17-2011 10:09 PM #12
Short analysis and common sense on use of various Octane gasoline for performance car
Performance Cars/Engines require higher Octane gasoline:
First of all, let's face the fact, that in Europe where most performance cars come from (and their engines for a BMW, Bentley, Mercedes, Audi, Ferrari, Lambo, Maserati, Porsche, etc.), the lowest Octane rating is around 97 and usually 99 to 102 is recommended.
So here's the quick answer to the question why high-performance engines blow in super cars blow up after approx. 20,000 -30,000 miles or so, besides the usual high RPM's, the 91 Octane gasoline at U.S. gas stations just isn't good quality gasoline for such engines. These engines are made for at least 97 Octanes. I sold my Jags, Bentleys, etc. because of that very fact, because it's impossible to even find 93 or preferably 95 Octanes anywhere ourdays. It's just too risky to spend a lot of money on a nice ride when its future (the engine's future) is not certain. I rather drive a Porsche (like the Panamera), Jag (XJ or XF) or whatever else too, but it's just too risky, ... and sure many may have the argument that one only own it for a few years anyway, but since I wouldn't buy it new but slightly used instead, I'm at a higher risk of having a blown engine. Just ask lots of previous Lamborghini owners or even BMW 750 owners and many will tell you their stories of engine problems down the road.
The Math on Driving U.S. Cars recommended with 87 Octanes with now 89 Octane gasoline instead:
Now I've tested the following on many U.S. cars from Cadillacs, Lincolns, Chevys (cars and SUVs/Pickup Trucks). Usually the recommended Octane rating for the gasoline is 87 on these cars. So I've tried over tens of thousands of miles using 89 Octane gasoline instead.
Now what is the result?
Well, usually the fuel economy with 89 octane gasoline is better by about approx. 8% ... almost always on average.
The difference between 89 octane gasoline vs. 87 octane gasoline is usually just about 10 Cents depening, but approx. 3.5-4% higher than the 87 octane gasoline. In effect using 89 octane gasoline saves overall approx. 4% which makes it more efficient to use the 89 octane rated gasoline, ... at least in my tests (based on pocket book and perhaps not too scientific) over approx. 12+ years or so in various U.S. vehicles. So I always use 89 octanes in my Lincoln Town Cars, Chevy Avalanches, Cadillac Devilles, etc. and I save the 4% which is a lot over a decade or so, especially with today's gas prices.
And also, there's no denying that higher octane gas, or at least the mid-grade 89 vs. the regular 87 makes the engine run indeed smoother without knocks, etc. and performance seems a bit better. So maybe I'm just one of the few who loves to drive and does use the 89 octane gasoline instead (based on the general stats of 89 octane consumption in the U.S.), but again it's more efficient to use 89 octane gasoline and it's certainly better for the engine.
02-15-2012 02:27 AM #13
: BMW explains using lower Octane gasoline
Great post, although I would also note that adding word restriction to your comments might backfire. I understand wanting to cut down on spam, but it also adds another barrier for the commenter, and I think it's more beneficial to make commenting as easy as possible.
03-06-2012 05:49 PM #14
I must say, I recently tanked up on regular in my 128i out of habit (new car for me) and I thought to myself all day that the car didn't seem to be picking up as much, wondering if I was just getting used to it and it didn't seem as quick. Now I may have mky answer - never even thought of it till I stumbled across this thread.
05-17-2012 04:58 AM #15
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