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[MadPoet]

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I have a question, is it possible that the oil companies would add certain additives to their premium brands that would give the illusion of "more power" to market their most expensive product through positive experiences such as engine noise & torque?

The reason I ask is that my Nissan Altima as well as my Buick century sound better on premium on long trips. While I understand that the octane rating has nothing to do with performance except when it comes to high performance engines like race boats and so on, I still think my cars sound and run a lot smoother on premium. Sorry for the run on sentences.


Yamaha vstar 650 midnight custom

 

[invictus43]

I have a question, is it possible that the oil companies would add certain additives to their premium brands that would give the illusion of "more power" to market their most expensive product through positive experiences such as engine noise & torque?

The reason I ask is that my Nissan Altima as well as my Buick century sound better on premium on long trips. While I understand that the octane rating has nothing to do with performance except when it comes to high performance engines like race boats and so on, I still think my cars sound and run a lot smoother on premium. Sorry for the run on sentences.


Yamaha vstar 650 midnight custom

I suppose I shall pick up the torch..sigh..

Many automobile engines have a knock sensor. If the computer detects detonation, it will decrease the amount of timing advance to prevent the detonation. At the same time, you will lose power. If there is no knock, as you would get with higher octane fuel, the computer will allow more timing advance to give you more power. The amount of timing change obviously has upper and lower limits. So you do indeed likely have more power and a smoother engine with higher octane in your car. The thing is, most bikes don't have knock sensors so they have no way to take advantage of more ignition timing, nor to prevent damage to your engine should you use inferior octane to what is specified.

Can low octane damage your engine? Definitely. Would a modern car with a knock sensor and an ECU suffer serious engine damage from low octane? Probably not. Detonation can burn valves, put holes in pistons and break-down lubrication film on bearings and piston skirts. A seriously high compression engine with lots of timing can self-destruct in short order on poor fuel.

Finally, with respect to ethanol, there's nothing wrong with it on modern engines. Modern fuel systems are designed to work with ethanol just fine. The problem is, ethanol has half the energy that gasoline has. So you need twice as much to make as big a bang. On open-loop systems, like most motorcycles, the effect is to lean out the mixture..since it doesn't have a closed loop system to determine how rich or lean the mixture is. On a car, the O2 sensor will determine the mixture and simply add more fuel. So you do end up with less mileage in either case.

 

[MadPoet]

I suppose I shall pick up the torch..sigh..

Many automobile engines have a knock sensor. If the computer detects detonation, it will decrease the amount of timing advance to prevent the detonation. At the same time, you will lose power. If there is no knock, as you would get with higher octane fuel, the computer will allow more timing advance to give you more power. The amount of timing change obviously has upper and lower limits. So you do indeed likely have more power and a smoother engine with higher octane in your car. The thing is, most bikes don't have knock sensors so they have no way to take advantage of more ignition timing, nor to prevent damage to your engine should you use inferior octane to what is specified.

Can low octane damage your engine? Definitely. Would a modern car with a knock sensor and an ECU suffer serious engine damage from low octane? Probably not. Detonation can burn valves, put holes in pistons and break-down lubrication film on bearings and piston skirts. A seriously high compression engine with lots of timing can self-destruct in short order on poor fuel.

Finally, with respect to ethanol, there's nothing wrong with it on modern engines. Modern fuel systems are designed to work with ethanol just fine. The problem is, ethanol has half the energy that gasoline has. So you need twice as much to make as big a bang. On open-loop systems, like most motorcycles, the effect is to lean out the mixture..since it doesn't have a closed loop system to determine how rich or lean the mixture is. On a car, the O2 sensor will determine the mixture and simply add more fuel. So you do end up with less mileage in either case.

Thanks for the explanation.


Yamaha vstar 650 midnight custom

 

[FriendlyFoe]

I know what octane means, you clearly dont know enough about it to answer my question.

I built a seadoo engine that required 110 octane. I know why it required that fuel and what would happen if I used pump gas.

LoL i love how clever people are on the internet. If you understand what running lower octane then required would do to a seadoo, the exact same thing would happen to any engine, including your bike. The answers are in there, look harder. It wouldn't get bad fuel mileage at all if you used lower octane, it would actually run the best it ever has right up until it started pinging and blew up the engine.

Modern cars can get away with running different fuels because of the knock sensor and multiple timing maps. Cars from the last 10 or so years will keep switching spark advance tables until it senses knock, then go back one table, so they can run on anything that comes out of the pumps.

I dont know much about modern fuel injection on bikes and if they've started using 02/knock sensors or not. If not as stated above the bike just runs off a set table (open loop) and will not adjust if there is detonation.

 

[DJM]

I actually run Shell 91 in my boat even though it specifies 87. It allows me to run 4 degrees more advanced timing and pick up a little bottom and midrange power plus I don't have to deal with the evils of ethanol. I'm sure you could take advantage of this in any vehicle with a conventional distributor.

 

[FriendlyFoe]

I actually run Shell 91 in my boat even though it specifies 87. It allows me to run 4 degrees more advanced timing and pick up a little bottom and midrange power plus I don't have to deal with the evils of ethanol. I'm sure you could take advantage of this in any vehicle with a conventional distributor.

Yup, altho from the bit i know i think if compression is really low the gains from advancing timing for higher octane fuel are negligible.

 

[01cbr]

LoL i love how clever people are on the internet. If you understand what running lower octane then required would do to a seadoo, the exact same thing would happen to any engine, including your bike. The answers are in there, look harder. It wouldn't get bad fuel mileage at all if you used lower octane, it would actually run the best it ever has right up until it started pinging and blew up the engine.

Modern cars can get away with running different fuels because of the knock sensor and multiple timing maps. Cars from the last 10 or so years will keep switching spark advance tables until it senses knock, then go back one table, so they can run on anything that comes out of the pumps.

I dont know much about modern fuel injection on bikes and if they've started using 02/knock sensors or not. If not as stated above the bike just runs off a set table (open loop) and will not adjust if there is detonation.

Lol too bad google can't teach you how to ready. None of your yammering has made any sense in relation to my question.

 

[FriendlyFoe]

simple enough for ya?

Honest question.
Are there any issues with running a lower than recommended octane fuel in a EFI engine other than horrible fuel mileage?

Other issues. Yes the motor might blow up. You will in fact get better mileage

 

[01cbr]

Let me put this in terms you might understand.

In a modern car that compensates for knocking due to lower than necessary octane, what are the long term effects?

 

[01cbr]

simple enough for ya?



Other issues. Yes the motor might blow up. You will in fact get better mileage

Thats funny because both cars that I owned that required 91 octane got WORSE mileage on 87.

Yes people are so clever on the internet.....well at least you try to be.

 

[FriendlyFoe]

Knowing what your asking would help! seeing as how we're mostly talking about bikes and bikes cant do that.

Just a loss of efficiency and power. With high compression you'd have to back off a lot of timing to run low octane, this is not ideal. If you know engines thats kind of common sense no?

 

[FriendlyFoe]

Thats funny because both cars that I owned that required 91 octane got WORSE mileage on 87.

Yes people are so clever on the internet.....well at least you try to be.

If you did understand what octane means you would understand why higher octane then the engine can use would result in an incomplete burn. This is not more efficient.

EDIT: okay had to read that again. See post above. Running a high compression engine on low octane with backed off timing is not efficient either.

The comment quoted is about using higher octanes then required. Your cars engine would explode if it ran the same timing on 87 it did on 91

 

[01cbr]

Knowing what your asking would help! seeing as how we're mostly talking about bikes and bikes cant do that.

Just a loss of efficiency and power. With high compression you'd have to back off a lot of timing to run low octane, this is not ideal. If you know engines thats kind of common sense no?

Dude I wrote the question in response to quotes about a prelude.
You responded like a ******, you dont even have a clue what im asking, and you dont have the knowledge to back it up so just stop.

 

[Low rider]

My bike's owners manual states 87 octane.
Anything higher and my bike runs rough.

 

[NP6000]

Let me put this in terms you might understand.

In a modern car that compensates for knocking due to lower than necessary octane, what are the long term effects?

01cbr, In a modern car that has knock control your fuel mileage will suffer, but only in areas of the operating regime that have spark knock tendencies. In my experience that is mostly WOT or near WOT operating points.

Additionally using low grade fuel when high grade is called for increases the risk of pre-ignition at low speed high load conditions (note that spark knock and pre ignition are two totally different events.) This is where high octane fuel can save the engine from self destruction.

The reason for this loss in fuel mileage is because your cylinder peak pressure location is retarded beyond the optimal values. Combustion engineers use a few rule of thumbs for optimal mechanical efficiency with respect to combustion. You generally look for peak pressure to be at 10-15 degress ATDC, and another measure called CA50 (which is the crank angle that 50% of the charge mixture has burned) which occurs between 7-9 degrees ATDC.

When you retard spark timing due to active knock control you cause these values to fall outside of this range, reducing mechanical efficiency.

Given that knock control is mostly active at WOT or near WOT, I think the change in observed mileage is due to ethanol content and less so for octane number.

Fiinally, in a new vehicle that calls for pump octane 91 or higher, you run the risk of pre-ignition damage. Note the knock control cannot detect pre-ignition, it only detects spark knock. Newer automatic transmission shift strategies are much more aggressive with lots of locked torque converter operation and lots of low speed high load conditions to improve fuel economy. This is prime for pre-ignition events, as witnessed by early ford 3.5V6 eco-boost, as well as the Hyundai 2.0T. Ford had changed the shift strategy to avoid operation in areas at risk for pre-ignition, and I have yet to see many Hyundai failures in the field.

As an aside, the new skyactiv from mazda has ion sensing through the spark plugs, and that is the only system that I know of that can detect pre-emptively detect pre-ignition.

 

[01cbr]

01cbr, In a modern car that has knock control your fuel mileage will suffer, but only in areas of the operating regime that have spark knock tendencies. In my experience that is mostly WOT or near WOT operating points.

Additionally using low grade fuel when high grade is called for increases the risk of pre-ignition at low speed high load conditions (note that spark knock and pre ignition are two totally different events.) This is where high octane fuel can save the engine from self destruction.

The reason for this loss in fuel mileage is because your cylinder peak pressure location is retarded beyond the optimal values. Combustion engineers use a few rule of thumbs for optimal mechanical efficiency with respect to combustion. You generally look for peak pressure to be at 10-15 degress ATDC, and another measure called CA50 (which is the crank angle that 50% of the charge mixture has burned) which occurs between 7-9 degrees ATDC.

When you retard spark timing due to active knock control you cause these values to fall outside of this range, reducing mechanical efficiency.

Given that knock control is mostly active at WOT or near WOT, I think the change in observed mileage is due to ethanol content and less so for octane number.

Fiinally, in a new vehicle that calls for pump octane 91 or higher, you run the risk of pre-ignition damage. Note the knock control cannot detect pre-ignition, it only detects spark knock. Newer automatic transmission shift strategies are much more aggressive with lots of locked torque converter operation and lots of low speed high load conditions to improve fuel economy. This is prime for pre-ignition events, as witnessed by early ford 3.5V6 eco-boost, as well as the Hyundai 2.0T. Ford had changed the shift strategy to avoid operation in areas at risk for pre-ignition, and I have yet to see many Hyundai failures in the field.

As an aside, the new skyactiv from mazda has ion sensing through the spark plugs, and that is the only system that I know of that can detect pre-emptively detect pre-ignition.

Thank you, what I was looking for.

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