Octane and Mileage

[bloodmack]

people still believe this shit? Its common sense man. Unless you tune your car for a different Octane nothing will change. If you put a different octane in your tank when your air and fuel mix and get compressed it could combust earlier or later then its supposed to.

[freakshow]

Originally Posted by dangonay

I'd say the performance aspect is probably in her head, even if her car was actually performing better.

I'll try to explain this simply to hopefully get my point across.

Engine ECU's have what are known as "adaptations". Adaptations are what allow engines to perform consistently as operating conditions change (quality of fuel, age of engine, wear of components and so on). In simple terms, adaptations are a set of numbers which tells the ECU how to modify engine parameters like fuel & ignition.

<going to spoiler the rest for length>

Spoiler!

Let's say at a certain RPM and load the ECU has a value of 20 degrees of timing stored. When the engine is running and the ignition is fired at 20 degrees the engine detects knock. So it pulls back the timing to 18 degrees and there's still a knock. It pulls timing back to 16 degrees and the knock goes away.

If this happened once-in-awhile, the ECU would not bother changing the adaptations as it can handle the occasional knock by simply pulling timing. If it's happening regularly, then the ECU might store a value of -4 degrees as an "adaptation" for ignition. The next time the engine reaches the same RPM and load, the ECU gets the 20 degree value from memory and applies the adaptation to it (in this case, -4 degrees) and then fires the ignition at 16 degrees. Knock is eliminated not because the knock sensors detected it and the ECU adjusted timing, but because the timing amount was already corrected by applying an adaptation.

It can get a lot more complicated than this, but this is a general idea how adaptations work.

One key thing to remember about adaptations is it takes time for the ECU to set adaptations. It depends on the car but it can take anywhere from 15 minutes to several hours before the ECU has enough data from various driving conditions to set adaptations. This is why when your mom switches from lower octane to higher octane fuel she likely wouldn't feel an instant increase in power because the ECU would have set its adaptations for the lower quality fuel. Her car will perform better, but it will take some driving before the ECU adapts to the new fuel.


Edit: Just saw the car is a CR-V. In that case, she's just imagining things. If it was a car that required higher octane, then everything I said above applies.

Lets say you run 89 fuel on a car that requires 91, the adaptation gets set to -4 over a few hours. In 4 months time, you decide to switch back to 91, how does the engine decide when to change the adaptation back to 0 instead of pre-applying the value?

[PornMaster]

Results are in
got 465km on the tank
usually I get 425 with 87, when I pumped it clicked at 59.xxxL so there was 1 litre away.

Not sure if its worth the extra $7

[bcrdukes]

^
Did your driving route change, by chance? i.e. any highway driving more than usual?

The weather is slowly getting warmer too but that shouldn't make that huge of a difference.

[dangonay]

Originally Posted by freakshow

Lets say you run 89 fuel on a car that requires 91, the adaptation gets set to -4 over a few hours. In 4 months time, you decide to switch back to 91, how does the engine decide when to change the adaptation back to 0 instead of pre-applying the value?

ECU's are always adjusting values to run at optimal efficiency. They do this by intentionally varying actual ignition/injection values by a small amount away from "normal" and monitoring sensors to see the results, and, if necessary, further adjusting adaptations. In fact, adaptations are always being adjusted over the life of the vehicle, usually only by very small amounts.

That said, an engine can adapt very quickly to lower octane fuel because knock will occur far more often. Switching to higher octane would take longer to adjust adaptations simply because there's no "immediate" change that the ECU would see.

Another example of this (though not related to adaptations) is an oxygen sensor response test. The ECU would intentionally make the mixture richer by increasing injector pulse width and then monitoring how long it takes for the oxygen sensor to respond. A good sensor should respond very quickly (perhaps 100ms) while a bad sensor might take much longer (600ms or more). If the sensor takes too long, you will get a check engine light and a code that says something like "O2 Sensor Aged" or "O2 Sensor Dynamic Response".

[PornMaster]

Originally Posted by bcrdukes

^
Did your driving route change, by chance? i.e. any highway driving more than usual?

The weather is slowly getting warmer too but that shouldn't make that huge of a difference.

Stayed routine

[1exotic]

My Jay-Dee-M vehicle is mapped for 98 RON gasoline which is about 94-95 Octane reading here... so I'm pretty much stuck on 94 Chevron. Tried 91 with Shell before but I noticed the mileage went down a bit.

[mr_chin]

I've been using 94 octane ever since I bought my car.

Here is my car's fuel recommendation

Your vehicle is designed to operate
on unleaded gasoline with a pump
octane number of 87 or higher. Use
of a lower octane gasoline can cause
a persistent, heavy metallic rapping
noise that can lead to engine damage.

You may hear a knocking noise from
the engine if you drive the vehicle at
low engine speed (below about 1,000
rpm) in a higher gear. To stop this,
raise the engine speed by shifting to
a lower gear.

We recommend using quality
gasolines containing detergent
additives that help prevent fuel
system and engine deposits.

In addition, in order to maintain good
performance, fuel economy, and
emissions control, we strongly
recommend, in areas where it is
available, the use of gasoline that
does NOT contain manganese-based
fuel additives such as MMT.

Use of gasoline with these additives
may adversely affect performance,
and cause the malfunction indicator
lamp on your instrument panel to
come on. If this happens, contact
your authorized dealer for service.

Will switching back to 87 octane mess up the timing?

And what would the bold line mean? Is ethanol considered detergent additive?

[Groot]

Anyone see this? Found it kinda interesting but wished they did a long term run.

http://www.cbc.ca/marketplace/episod...mpfiction.html

[Amuse]

Originally Posted by !SG

i switched to shell.

91/92 octane w/ no ethanol mix.

Chevron 91 has any ethanol mix?

I noticed my car runs better on Canadian Chevron 91 compared to Pt. Roberts Chevron 92.

[broken_arrow]

Correct me if I'm wrong, but Shell V-Power now has ethanol, unless the pump specifically states no ethanol...

Anyways, I use Chevron 94. I get about 340-360 km out of a 70L tank... All city driving.

[dangonay]

Originally Posted by Kushy

Anyone see this? Found it kinda interesting but wished they did a long term run.

Pump Fiction - Marketplace

Saw that the other day. Though they are essentially correct in stating it's a waste putting higher octane gas than what your vehicle recommends, some of their test methods are seriously flawed.

For example, when the mechanic had the vehicle hooked up to a gas analyzer to monitor the exhaust emissions. Anyone who has ever used an analyzer (like trying to get cars to pass Aircare) knows that readings change even from minute to minute. There's no way you could drive a car on one tank of 87 octane, measure the readings, and then drive on a tank of premium and measure the readings again, and get any kind of meaningful result that you could attribute to the different gas. Even a difference in the weather from one day to the next could affect readings. Or the engine temperature (how long did the vehicle run before each test). Or the adaptations (which have been discussed already).

Gas analyzers are only really useful for measuring large changes or to monitor changes while you're specifically changing something (like adjusting a carb). They are absolutely useless as any form of data gathering device.

Has anyone gone to Aircare and failed then gone back and passed? That tells you right there how accurate gas analyzers are.

[mr_chin]

Originally Posted by broken_arrow

Correct me if I'm wrong, but Shell V-Power now has ethanol, unless the pump specifically states no ethanol...

Anyways, I use Chevron 94. I get about 340-360 km out of a 70L tank... All city driving.

Dayum, what car do you drive??

I guess it's not THAT big of a deal with 94 vs 87. The difference in like approximately $7 more and it's a peace of mind knowing I'm running on non-ethanol fuel.

[broken_arrow]

Originally Posted by mr_chin

Dayum, what car do you drive??

I guess it's not THAT big of a deal with 94 vs 87. The difference in like approximately $7 more and it's a peace of mind knowing I'm running on non-ethanol fuel.

BMW M6

[xilley]

Originally Posted by broken_arrow

BMW M6

so cocky and proud

[EvoLove]

lol my car calls for premium unleaded =.= i use both chevron 94 i get 300km but when i use shell 91 no ethanol i get 350 on a 50L tank =.= so im

[dared3vil0]

I used to drive a 2000 Nissan Maxima, It was reccomended to use 91, I used 87 for a month or two, I averaged 14.3 l/100km, I used 91 like it said to, I averaged 11.2 l/100km. So yes, You WILL hurt fuel economy by using a lesser octane than you should be. Higher octane than reccomended IS a waste of money however.

[keitaro]

Originally Posted by dangonay

ECU's are always adjusting values to run at optimal efficiency. They do this by intentionally varying actual ignition/injection values by a small amount away from "normal" and monitoring sensors to see the results, and, if necessary, further adjusting adaptations. In fact, adaptations are always being adjusted over the life of the vehicle, usually only by very small amounts.

That said, an engine can adapt very quickly to lower octane fuel because knock will occur far more often. Switching to higher octane would take longer to adjust adaptations simply because there's no "immediate" change that the ECU would see.

Another example of this (though not related to adaptations) is an oxygen sensor response test. The ECU would intentionally make the mixture richer by increasing injector pulse width and then monitoring how long it takes for the oxygen sensor to respond. A good sensor should respond very quickly (perhaps 100ms) while a bad sensor might take much longer (600ms or more). If the sensor takes too long, you will get a check engine light and a code that says something like "O2 Sensor Aged" or "O2 Sensor Dynamic Response".

I actually had this issue happen. Kept getting "O2 Sensor Slow Response" CEL. Eventually, I changed the O2 sensor, and noticed that I was getting better gas millage.

[sonick]

Originally Posted by Kushy

Anyone see this? Found it kinda interesting but wished they did a long term run.

Pump Fiction - Marketplace

LOL the instructor running the dyno at the Canadian Auto & Trucking College thought that it would make a difference, what a shitty teacher.

And asking the gas pumpers what is cleaner? Who does CBC think they are, Fuel Sommeliers? It's not like they go through a rigorous product training course before they start working, what would they know?

Whole video is pretty misleading to the general public to say the least.

[Manic!]

It's amazing how someone will trust someone making minimum wage at a gas station over what the manufacture recommends.

[mx555]

Originally Posted by mr_chin

I've been using 94 octane ever since I bought my car.

Here is my car's fuel recommendation



Will switching back to 87 octane mess up the timing?

And what would the bold line mean? Is ethanol considered detergent additive?

Quality is not measured by octane. Those lines simply means don't buy gas from shady dudes from the back of their van.

Ethanol is not a detergent additive; it is an octane booster.

10% ethanol blend equates to roughly 3 points increase in octane. So, the 87 w/ 10% ethanol @ Chevron is actually more like 84-86 + ~3 octane from the ethanol.

Companies like Chevron, Shell, and Petro Canada are all what are referred to as "top-tier" distributors. This means that the gas that they sell is guaranteed to meet the minimum required qualities and detergent levels mandated by the EPA.
Generally speaking you're getting much more than EPA standards for detergents in your gasoline, for example, Shell's V power simply means that there are 5x the mandated amount of detergents. The mandated amount of detergents does NOT clean the engine, it only prevents more build up.
87 to 94, they all come from the same fuel farm, same pipeline. The differences between them is the amount of octane boosters blended in prior to distribution; this is also where each company blends in their additives.

Problems with alcohols:
-hydroscopic (absorbs water)
-fixed volatility (each molecule is the same size and configuration. meaning they volatize at the same temperature. gas is comprised of many different sized hydrocarbons. Light ends (short chains) are the molecules that evaporate first (good for cold starting), heavy ends are the ones that contain the most energy.
-less energy per unit compared to gasoline
-removes oil from the combustion chambers of 2 stroke motors =(


Oh PS, that 87 octane you bought from Chevron? Ya, that's more like 89 octane. The octane rating at the pump is a LEGAL MINIMUM, so they're always higher than advertised.

[broken_arrow]

Originally Posted by xilley

so cocky and proud

[mr_chin]

Originally Posted by mx555

Quality is not measured by octane. Those lines simply means don't buy gas from shady dudes from the back of their van.

Ethanol is not a detergent additive; it is an octane booster.

10% ethanol blend equates to roughly 3 points increase in octane. So, the 87 w/ 10% ethanol @ Chevron is actually more like 84-86 + ~3 octane from the ethanol.

Companies like Chevron, Shell, and Petro Canada are all what are referred to as "top-tier" distributors. This means that the gas that they sell is guaranteed to meet the minimum required qualities and detergent levels mandated by the EPA.
Generally speaking you're getting much more than EPA standards for detergents in your gasoline, for example, Shell's V power simply means that there are 5x the mandated amount of detergents. The mandated amount of detergents does NOT clean the engine, it only prevents more build up.
87 to 94, they all come from the same fuel farm, same pipeline. The differences between them is the amount of octane boosters blended in prior to distribution; this is also where each company blends in their additives.

Problems with alcohols:
-hydroscopic (absorbs water)
-fixed volatility (each molecule is the same size and configuration. meaning they volatize at the same temperature. gas is comprised of many different sized hydrocarbons. Light ends (short chains) are the molecules that evaporate first (good for cold starting), heavy ends are the ones that contain the most energy.
-less energy per unit compared to gasoline
-removes oil from the combustion chambers of 2 stroke motors =(


Oh PS, that 87 octane you bought from Chevron? Ya, that's more like 89 octane. The octane rating at the pump is a LEGAL MINIMUM, so they're always higher than advertised.

It is said that ethanol is the culprit of engine knocking sounds, like someone through screws into the piston chambers.

Is this true?

Overall, is ethanol good for your engine? Or does it damage it over time?

[radioman]

Originally Posted by broken_arrow

Those BMW drivers......

[mx555]

Originally Posted by mr_chin

It is said that ethanol is the culprit of engine knocking sounds, like someone through screws into the piston chambers.

Is this true?

Overall, is ethanol good for your engine? Or does it damage it over time?

Ethanol increases octane, reduces detonation.

@ current 10% blends and at near future 15% blends, your not doing anything detrimental to your car. Higher blends will start to be corrosive to the plastic/rubber parts of fuel systems in older cars. Most affected will be the 2-strokes n rotaries.