[The X Men]

Originally Posted by BMWrules7

Don't forget, everything has a tolerance. So, 89 could be 87 or 92.

Thus, you would be better of going with a mid-grade if you decide to be Mr. Cheapypants in your fancy shmancy deluxe BMW. So, a mid grade 91 could be a 89 or a 93.

Exactly, everything has a tolerance. Its possible that BMW tune the engine to run on 89 octane, but reccommand 91 to be one the safe side.

[ric124]

Originally Posted by The X Men

Exactly, everything has a tolerance. Its possible that BMW tune the engine to run on 89 octane, but reccommand 91 to be one the safe side.

I think they actually tuned for 91 and you may run on 89 if needed but you may hear some knocking as stated in the manual.

[RPM90]

Originally Posted by The X Men

Exactly, everything has a tolerance. Its possible that BMW tune the engine to run on 89 octane, but reccommand 91 to be one the safe side.

You can believe whatever you want.

However, the science and engineering behind this is not a belief system.

It's been stated many times over and over on this and other threads about octane and BMW. BMW, as other manufacturers do, provide tuning and maps so that the engine will run on different octane rated gasolines.
Your engine will run on 87 octane, but how well it will run is a different thing.
89 is the minimum and 91 is recommended according to the post above.
So, run 91 minimum and you'll be just fine.

Your engine can run on the lower 89 octane fuel because the system uses sensors to determine how the engine is running. If the engine is running well on lower octane the ECU will try and advance timing to give optimal performance.
As it advances timing it continues to monitor performance.
There are optimal timing maps and less than optimal maps. The ECU determines which to use based on sensor readings.
If you're using 87 octane fuel, then the ECU will advance timing as far as that octane rating will allow for the type of driving you are doing. As it encounters knock timing is retarded to keep the engine running safely. As timing is retarded, optimal performance and peak power are reduced.

If you then use 89 octane fuel the ECU will again monitor and advance, the retard as needed.
Can you get peak engine output with lower octane fuel?
Yes, it can happen, IF conditions allow, meaning, the ambient air is cold and you're not getting any knock. If that happens, then you can still get peak output, that is until knock shows itself. Then, timing gets retarded and power reduced.
Keep in mind, conditions are not always ideal, and knock conditions occur more frequently with lower octane fuel. So just because it can/might run peak power, that doesn't mean it will be consistent or for long.

That's why higher octane fuels are recommended if you want peak performance most of the time. With higher octane fuel, there is reduced change of knock, and when knock occurs and timing gets reduced, recovery back to optimal is much quicker as higher octane is more resistant to knock events.
This is also why running 93 octane can provide a greater cushion for knock. Higher octane (91 in this case according to BMW) fuel allows our engines to run their best for longer periods between knock events, and will allow peak timing advance to recover quicker.

91 is recommended, and tuned for, because that is the best octane level sold in some states. That means, if you use 91 AKI fuel, then you can expect to achieve the specified power output. Dyno's have shown that even in some cars where 91 is recommended, there can be power gain when 93 is used, which shows the ECU has the tuning to maximize power when higher octane is used. That can only happen if the tuning is there for higher octane. If it's not, then you won't get any more power using 93 vs 91.
Can the N20 or N55 develop more power using 92 or 93 octane vs using 91? Dyno runs would have to be done to demonstrate that potential.

89 is not the octane tuned for and 91 is the cushion. 89 can be used because of the build in cushions, and that doesn't mean you are running at peak performance when doing so.

[ric124]

Originally Posted by RPM90

You can believe whatever you want.

However, the science and engineering behind this is not a belief system.

It's been stated many times over and over on this and other threads about octane and BMW. BMW, as other manufacturers do, provide tuning and maps so that the engine will run on different octane rated gasolines.
Your engine will run on 87 octane, but how well it will run is a different thing.
89 is the minimum and 91 is recommended according to the post above.
So, run 91 minimum and you'll be just fine.

Your engine can run on the lower 89 octane fuel because the system uses sensors to determine how the engine is running. If the engine is running well on lower octane the ECU will try and advance timing to give optimal performance.
As it advances timing it continues to monitor performance.
There are optimal timing maps and less than optimal maps. The ECU determines which to use based on sensor readings.
If you're using 87 octane fuel, then the ECU will advance timing as far as that octane rating will allow for the type of driving you are doing. As it encounters knock timing is retarded to keep the engine running safely. As timing is retarded, optimal performance and peak power are reduced.

If you then use 89 octane fuel the ECU will again monitor and advance, the retard as needed.
Can you get peak engine output with lower octane fuel?
Yes, it can happen, IF conditions allow, meaning, the ambient air is cold and you're not getting any knock. If that happens, then you can still get peak output, that is until knock shows itself. Then, timing gets retarded and power reduced.
Keep in mind, conditions are not always ideal, and knock conditions occur more frequently with lower octane fuel. So just because it can/might run peak power, that doesn't mean it will be consistent or for long.

That's why higher octane fuels are recommended if you want peak performance most of the time. With higher octane fuel, there is reduced change of knock, and when knock occurs and timing gets reduced, recovery back to optimal is much quicker as higher octane is more resistant to knock events.
This is also why running 93 octane can provide a greater cushion for knock. Higher octane (91 in this case according to BMW) fuel allows our engines to run their best for longer periods between knock events, and will allow peak timing advance to recover quicker.

91 is recommended, and tuned for, because that is the best octane level sold in some states. That means, if you use 91 AKI fuel, then you can expect to achieve the specified power output. Dyno's have shown that even in some cars where 91 is recommended, there can be power gain when 93 is used, which shows the ECU has the tuning to maximize power when higher octane is used. That can only happen if the tuning is there for higher octane. If it's not, then you won't get any more power using 93 vs 91.
Can the N20 or N55 develop more power using 92 or 93 octane vs using 91? Dyno runs would have to be done to demonstrate that potential.

89 is not the octane tuned for and 91 is the cushion. 89 can be used because of the build in cushions, and that doesn't mean you are running at peak performance when doing so.

+++++1

[ric124]

So I guess some ppl rather retarded performance to save $1 give or take a few cents.

Reg - 87
Mid - 89
pre - 93

[batislav]

Originally Posted by RPM90

You can believe whatever you want.

However, the science and engineering behind this is not a belief system.

It's been stated many times over and over on this and other threads about octane and BMW. BMW, as other manufacturers do, provide tuning and maps so that the engine will run on different octane rated gasolines.
Your engine will run on 87 octane, but how well it will run is a different thing.
89 is the minimum and 91 is recommended according to the post above.
So, run 91 minimum and you'll be just fine.

Your engine can run on the lower 89 octane fuel because the system uses sensors to determine how the engine is running. If the engine is running well on lower octane the ECU will try and advance timing to give optimal performance.
As it advances timing it continues to monitor performance.
There are optimal timing maps and less than optimal maps. The ECU determines which to use based on sensor readings.
If you're using 87 octane fuel, then the ECU will advance timing as far as that octane rating will allow for the type of driving you are doing. As it encounters knock timing is retarded to keep the engine running safely. As timing is retarded, optimal performance and peak power are reduced.

If you then use 89 octane fuel the ECU will again monitor and advance, the retard as needed.
Can you get peak engine output with lower octane fuel?
Yes, it can happen, IF conditions allow, meaning, the ambient air is cold and you're not getting any knock. If that happens, then you can still get peak output, that is until knock shows itself. Then, timing gets retarded and power reduced.
Keep in mind, conditions are not always ideal, and knock conditions occur more frequently with lower octane fuel. So just because it can/might run peak power, that doesn't mean it will be consistent or for long.

That's why higher octane fuels are recommended if you want peak performance most of the time. With higher octane fuel, there is reduced change of knock, and when knock occurs and timing gets reduced, recovery back to optimal is much quicker as higher octane is more resistant to knock events.
This is also why running 93 octane can provide a greater cushion for knock. Higher octane (91 in this case according to BMW) fuel allows our engines to run their best for longer periods between knock events, and will allow peak timing advance to recover quicker.

91 is recommended, and tuned for, because that is the best octane level sold in some states. That means, if you use 91 AKI fuel, then you can expect to achieve the specified power output. Dyno's have shown that even in some cars where 91 is recommended, there can be power gain when 93 is used, which shows the ECU has the tuning to maximize power when higher octane is used. That can only happen if the tuning is there for higher octane. If it's not, then you won't get any more power using 93 vs 91.
Can the N20 or N55 develop more power using 92 or 93 octane vs using 91? Dyno runs would have to be done to demonstrate that potential.

89 is not the octane tuned for and 91 is the cushion. 89 can be used because of the build in cushions, and that doesn't mean you are running at peak performance when doing so.

Ha, you said science and engineering. People always want a short cut or "secret/special" aka fallacious knowledge to circumvent reality when it doesn't suit them.

[Mahzari]

I have been putting 89 octane into my 328i for the past 4 or 5 trips to the station. I have been averaging 26.3mpg with mixed city, freeway, traffic, and spirited driving. And I kept up with a Mustang GT (the old 4.6L)... sooo I'm sticking to 89 octane.

If I were tuned, I would go for 91 octane to get the most out of it, but since my car's stock there's no point.

[ric124]

Originally Posted by Mahzari

I have been putting 89 octane into my 328i for the past 4 or 5 trips to the station. I have been averaging 26.3mpg with mixed city, freeway, traffic, and spirited driving. And I kept up with a Mustang GT (the old 4.6L)... sooo I'm sticking to 89 octane.

If I were tuned, I would go for 91 octane to get the most out of it, but since my car's stock there's no point.

HUH! So you will continue using the minimum which may cause some knocking? BMW designed and ran all test on 91 octane but you may use 89 but the ecu will have to compensate and detune your engine. Meaning if 91 or higher is not around then use 89 but dont keep doing it.

This is why I will never buy a car that was a lease.

[EnerJi]

Originally Posted by ric124

HUH! So you will continue using the minimum which may cause some knocking? BMW designed and ran all test on 91 octane but you may use 89 but the ecu will have to compensate and detune your engine. Meaning if 91 or higher is not around then use 89 but dont keep doing it.

This is why I will never buy a car that was a lease.

Well in fairness, if he hears knocking (pinging), he could always switch to Premium, couldn't he? The manual itself says that some light pinging that occurs at start-up when outside temperatures are warm will not damage the engine.

[Mahzari]

Originally Posted by ric124

HUH! So you will continue using the minimum which may cause some knocking? BMW designed and ran all test on 91 octane but you may use 89 but the ecu will have to compensate and detune your engine. Meaning if 91 or higher is not around then use 89 but dont keep doing it.

This is why I will never buy a car that was a lease.

The manual states that 89 is the minimum, just like 91 is the minimum on an M3. I live in California, where the highest they sell is 91, so what do you want me to do? Drive to AZ or NV to get 93 octane to put into my M3 so that you can sleep easily at night? You can live in your fantasy land where running 95 octane on a stock motor will give you more horsepower, but I live in reality where I am A) listening to the BMW owner's manual and B) driving a car that is under warranty.

You make it seem like I'm putting diesel (or sand) into my engine.

Originally Posted by EnerJi

Well in fairness, if he hears knocking (pinging), he could always switch to Premium, couldn't he? The manual itself says that some light pinging that occurs at start-up when outside temperatures are warm will not damage the engine.

Thank you

[ric124]

Originally Posted by Mahzari

The manual states that 89 is the minimum, just like 91 is the minimum on an M3. I live in California, where the highest they sell is 91, so what do you want me to do? Drive to AZ or NV to get 93 octane to put into my M3 so that you can sleep easily at night? You can live in your fantasy land where running 95 octane on a stock motor will give you more horsepower, but I live in reality where I am A) listening to the BMW owner's manual and B) driving a car that is under warranty.

You make it seem like I'm putting diesel (or sand) into my engine.

Thank you

Lol I could care less what u do with your car. I just think if BMW says in the manual they used 91 octane to obtain optimal hp then that's what I will use. 91 is rare here but the price difference between 89 and 93 is about $1 per tank.

[RPM90]

Originally Posted by EnerJi

Well in fairness, if he hears knocking (pinging), he could always switch to Premium, couldn't he? The manual itself says that some light pinging that occurs at start-up when outside temperatures are warm will not damage the engine.

Why guess when you can read what BMW says about which octane to use.

Taken from a post on roadfly.com:

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.

Now let's stop the nonsense.

[RPM90]

Originally Posted by Mahzari

The manual states that 89 is the minimum, just like 91 is the minimum on an M3. I live in California, where the highest they sell is 91, so what do you want me to do? Drive to AZ or NV to get 93 octane to put into my M3 so that you can sleep easily at night? You can live in your fantasy land where running 95 octane on a stock motor will give you more horsepower, but I live in reality where I am A) listening to the BMW owner's manual and B) driving a car that is under warranty.

You make it seem like I'm putting diesel (or sand) into my engine.

Thank you

This isn't about us sleeping or wanting you to do anything.
You can obviously do as you like.
What is being explained is that there is a difference in engine performance when using the lower "required" minimum octane fuel, and the "recommended" 91 octane fuel.

89 is listed as a "required" minimum, meaning the lowest octane fuel you should use. 91 is listed as the recommended octane for best performance, because the engine has been tuned to provide best power and best fuel efficiency. Less the 91, lower performance.
Simple.

As for who is living a fantasy, none of us who understand octane and engine tuning have stated nor promoted the incorrect notion that using higher octane fuel will magically give an engine more power.
We know that's not true. If an engine is designed and tuned for 89AKI, then using 95AKI will not make that engine produce more power, as it doesn't have the tuning to take advantage of a higher octane fuel.

Since your engine IS designed to produce it's best performance and greatest efficiency with 91 octane, then you are simply choosing to run your engine in a detuned state by using 89AKI.
Thinking that you are getting the same peak performance from 89 as you would with 91 puts you in fantasy land.

[Mahzari]

Originally Posted by RPM90

This isn't about us sleeping or wanting you to do anything.
You can obviously do as you like.
What is being explained is that there is a difference in engine performance when using the lower "required" minimum octane fuel, and the "recommended" 91 octane fuel.

89 is listed as a "required" minimum, meaning the lowest octane fuel you should use. 91 is listed as the recommended octane for best performance, because the engine has been tuned to provide best power and best fuel efficiency. Less the 91, lower performance.
Simple.

As for who is living a fantasy, none of us who understand octane and engine tuning have stated nor promoted the incorrect notion that using higher octane fuel will magically give an engine more power.
We know that's not true. If an engine is designed and tuned for 89AKI, then using 95AKI will not make that engine produce more power, as it doesn't have the tuning to take advantage of a higher octane fuel.

Since your engine IS designed to produce it's best performance and greatest efficiency with 91 octane, then you are simply choosing to run your engine in a detuned state by using 89AKI.
Thinking that you are getting the same peak performance from 89 as you would with 91 puts you in fantasy land.

I will gladly run against any stock 328i on 91 octane any time you want.

[ric124]

Originally Posted by Mahzari

I will gladly run against any stock 328i on 91 octane any time you want.

OK this thread needs to be closed.

its clear that you are smarter than the engineers at BMW.

[Mahzari]

Originally Posted by ric124

OK this thread needs to be closed.

its clear that you are smarter than the engineers at BMW.

I'm not saying I'm smarter, I just don't take their advice as the word of God. I am listening to their minimum requirement for fuel, but in some cases, like tire pressure, I don't listen to them at all. It does not make sense (in a car with the same size tires front and back and a 50.0/50.0 weight distribution) to have different tire pressures front to back, so I set all of my tires to 35psi and it drives better than it did stock.

Regardless, all I wanted to add was: I have not personally experienced any knocking, change in MPG, or perceivable change in performance by using 89 octane. That's all. Feel free to do whatever you want and feel free to ignore my experience.

[PavementIstRad]

I have also been using 89 in my 328i without any noticeable differences in fuel economy or performance. In my area premium is always 93 and recently it's been abount $.25 more per gallon to fill up with premium (93) vs mid-grade (89). So if I fill up once per week I am looking at an extra $600 during the course of my lease. Seems like a complete waste of money to fill up with premium to me when I can't even tell the difference (I did fill up with 93 the first month I had my car)... even if I didn't lease it would be hard for me to rationalize using premium when BMW says using 89 has no effect on engine life.

[BavarianFanatic]

Originally Posted by Mahzari

I'm not saying I'm smarter, I just don't take their advice as the word of God. I am listening to their minimum requirement for fuel, but in some cases, like tire pressure, I don't listen to them at all. It does not make sense (in a car with the same size tires front and back and a 50.0/50.0 weight distribution) to have different tire pressures front to back, so I set all of my tires to 35psi and it drives better than it did stock.

Regardless, all I wanted to add was: I have not personally experienced any knocking, change in MPG, or perceivable change in performance by using 89 octane. That's all. Feel free to do whatever you want and feel free to ignore my experience.

You do understand that tire pressures have a direct impact on the understeer/oversteer characteristics of the car don't you? That would be why they spec different pressures front/rear. It has zero to do with tire size. The 50/50 weight distribution AMPLIFIES the effects of tire pressure. A typical nose-heavy car will tend to understeer by default. A balanced car is on the hairy edge of wanting to oversteer (excluding alignment geometry for now).

The lesson here: do what you want with your own cars. But don't send anyone astray based on your own limited experiences. Especially when you can't back it up with facts. It's kind of like handing someone a revolver without checking to make sure the barrel is clear. "I pulled the trigger 5 times and nothing happened. I have no idea why it went off in his face."

[Mahzari]

Originally Posted by BavarianFanatic

You do understand that tire pressures have a direct impact on the understeer/oversteer characteristics of the car don't you? That would be why they spec different pressures front/rear. It has zero to do with tire size. The 50/50 weight distribution AMPLIFIES the effects of tire pressure. A typical nose-heavy car will tend to understeer by default. A balanced car is on the hairy edge of wanting to oversteer (excluding alignment geometry for now).

The lesson here: do what you want with your own cars. But don't send anyone astray based on your own limited experiences. Especially when you can't back it up with facts. It's kind of like handing someone a revolver without checking to make sure the barrel is clear. "I pulled the trigger 5 times and nothing happened. I have no idea why it went off in his face."

Yes, I understand tire pressures change how the car behaves. BMW recommends terrible tire pressures for regular cars (so that they understeer safely) and even tire pressures front and back for M cars (for a more neutral setup). That's also why a 335i Sport has a 30mm stagger front to back and an M3 only has a 20mm stagger.

I chose to apply the "M" tire pressures on my standard car with a square setup and even weight distribution so that it handles like a real car should.

[onehungevo]

I ran my Evo lean and it would knock with all gas 93 except Marathon.

[RPM90]

Originally Posted by Mahzari

I will gladly run against any stock 328i on 91 octane any time you want.