I have been trying different gas for a while. Right now I am using Petro-Canada 87. I keep an eye on the timing advancement to see how gas affects it. So far I am not very happy with Petro-Canada. Esso feels better and shows better ignition timing numbers. I will post my results some time later because It takes time for me to use up a full tank of fuel.
Maybe E-10 is better? - PentaStar (Flex Fuel)
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I did run a couple tanks of Esso's Synergy or whatever it's called in the Journey and noticed the vehicle felt peppier. Interesting about your observations.
So far since switching to esso 91 I haven't heard any pinging. That's the only perceivable difference so far. Obviously my car doesn't adjust timing electronically so all I can go by is the butt dyno. When you have 150hp at best and your car is very sensitive to changes in temperature it's hard to pin anything on the gasoline used. Also my gas mileage last 2 tanks was 15mpg and 13mpg, with warmup time to defrost windows quite a few days. My mileage will vary based on my schedule, where I have to drive and what the weather conditions are like. If it's not extremely cold and windows are clear I don't let it warm up more than 20 seconds.
Originally Posted by JHZR2
Originally Posted by Shannow
OK, can someone link me to something about octane disrupting the "explosion" and causing a stumble ?
I remember reading theory about that in the late 1990s. Essentially how running higher octane fuels when timing wasnt set for them could change combustion dynamics and complete burn. As I recall, it was also noted in relation to H2S odors from catalytic converters. No specific links, just recollection.
But since the late 90s, Id suspect that sensors and variable timing has made much of that further moot...
Octane is the resistance to autoignition of the bulk gasses at the end of combustion.
It's not ignition delay on the ignition from the spark, and it's not flame speed.
Originally Posted by Shannow
OK, can someone link me to something about octane disrupting the "explosion" and causing a stumble ?
I remember reading theory about that in the late 1990s. Essentially how running higher octane fuels when timing wasnt set for them could change combustion dynamics and complete burn. As I recall, it was also noted in relation to H2S odors from catalytic converters. No specific links, just recollection.
But since the late 90s, Id suspect that sensors and variable timing has made much of that further moot...
Octane is the resistance to autoignition of the bulk gasses at the end of combustion.
It's not ignition delay on the ignition from the spark, and it's not flame speed.
Using higher octane fuel needs a higher static or dynamic compression to be effective. I guess I don't use my words right. I.E. "not exploding correctly"........geez, sorry. If you don't have the squeeze, the burn/pop/boom might not be as good as 87 octane fuel. Tough crowd.......................
No, as I've stated.
The ignition process starts with the spark...there's a delay where the spark starts a flame...and flame speed in gasoline is pretty close to the same.
Unless you get into autoignition, which is what the octane is there for.
Higher octane does not need a higher compression to burn properly....it will burn at the same rate at a lower compression as a lower octane fuel (that is sufficiently far away from detonation). Lack of compression does not make high octane fuel "not burn".
The ignition process starts with the spark...there's a delay where the spark starts a flame...and flame speed in gasoline is pretty close to the same.
Unless you get into autoignition, which is what the octane is there for.
Higher octane does not need a higher compression to burn properly....it will burn at the same rate at a lower compression as a lower octane fuel (that is sufficiently far away from detonation). Lack of compression does not make high octane fuel "not burn".
I remember hearing basically the same thing as oldhp is saying years back, but I'm guessing it was just another myth like "you can't mix synthetic and conventional oil". So basically the only difference between octane levels is the resistance to autoignition? Until the fact that 91 usually has no ethanol, meaning more energy. Then there is another variable that can affect power and efficiency depending on the application.
I should be due for gas by tonight and I will refill with Esso 91 octane to see if it's the octane or brand of fuel. I'm leaning toward brand of fuel because I never had this issue in the past and never used Petro Canada either.
I'm looking forward to hearing the results.
Originally Posted by caprice_2nv
I'm looking forward to hearing the results.
I'm going to watch the ignition timing on my ScanGauge on the way home (to the fuel station) both on the highway and city traffic and then refill with the Esso gas at the low fuel light and see how that affects it.
I have lots of miles to do next week so it should be an excellent test case.
I'm looking forward to hearing the results.
I'm going to watch the ignition timing on my ScanGauge on the way home (to the fuel station) both on the highway and city traffic and then refill with the Esso gas at the low fuel light and see how that affects it.
I have lots of miles to do next week so it should be an excellent test case.
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Yes. The spark will ignite the mixture regardless of the octane rating. But in a high-compression engine, using octane lower than recommended will risk auto-ignition, and in this case the engine's computers will protect the engine by retarding the timing (or not advancing it as much). This will reduce power output.
Proper high octane fuel used in a high compression engine will effectively prevent auto-ignition and allow the engine computers to deliver more spark advance. And so the high compression engine will deliver more power with more spark advance, with no detonation.
Proper high octane fuel used in a high compression engine will effectively prevent auto-ignition and allow the engine computers to deliver more spark advance. And so the high compression engine will deliver more power with more spark advance, with no detonation.
High octane fuel burns slower to keep detonation at bay. Simple. It also burns slower in a lower compression engine. Simple. Worst case can cause a stumble while applying throttle. Simple. Throw in ethanol.....now it gets more un-simple. Hi-Ho-Silver!!! Away!!!
My 018 Caravan was stumbling when I first got it but put it off to computer learning my drive habits so I never thought it was fuel. I was running midgrade fuel for first 700 miles then regular fuel. Idle is smooth as glass now. What can attribute to the stumbling at idle is probably O2 sensor if richer at idle due to higher octane. The manual does state anything above 87 in one section but another states 87 is recommended. I can tell you I got 18.3 with midgrade and have averaged 19.4 accordingly to fuelly since I bought it. To hopefully improve mileage I am trying to run econ on for next 1000 miles or so. I might go back to midgrade to see if would be smoother when 40 mph and 900 rpms but now you have thinking I might have my not so smooth idle back if I do this.
I put the 91 octane in from low fuel light tonight at esso and it's stumbling worse than the Petro 91 so I'm going to run this tank out and try Esso 87 for a full tank.
I did run around after the fill with a couple hot starts.
Timing did advance with the 91 octane over the 87 previously by about 4 degrees or so
I did run around after the fill with a couple hot starts.
Timing did advance with the 91 octane over the 87 previously by about 4 degrees or so
Originally Posted by Shannow
Originally Posted by oldhp
High octane fuel burns slower to keep detonation at bay.!
No that's not the case...!!!
From Hemmings Daily Tech 101-Octane; The facts and fiction.
Because higher octane gas burns slower, it is more resistant to knock when subjected to higher RPM and cylinder pressures. Compression ratios also factor into cylinder pressures. Higher ratios cause higher cylinder pressures and therefore cause the engine to be more susceptible to pre-detonation or knock.
Originally Posted by oldhp
High octane fuel burns slower to keep detonation at bay.!
No that's not the case...!!!
From Hemmings Daily Tech 101-Octane; The facts and fiction.
Because higher octane gas burns slower, it is more resistant to knock when subjected to higher RPM and cylinder pressures. Compression ratios also factor into cylinder pressures. Higher ratios cause higher cylinder pressures and therefore cause the engine to be more susceptible to pre-detonation or knock.
Originally Posted by oldhp
Originally Posted by Shannow
Originally Posted by oldhp
High octane fuel burns slower to keep detonation at bay.!
No that's not the case...!!!
From Hemmings Daily Tech 101-Octane; The facts and fiction.
Because higher octane gas burns slower, it is more resistant to knock when subjected to higher RPM and cylinder pressures. Compression ratios also factor into cylinder pressures. Higher ratios cause higher cylinder pressures and therefore cause the engine to be more susceptible to pre-detonation or knock.
Link what you want...the explanation is wrong...
It IS, as I've posted, the resistance to autoignition.
Gasoline flame speed is virtually identical regardless of octane rating.
Originally Posted by Shannow
Originally Posted by oldhp
High octane fuel burns slower to keep detonation at bay.!
No that's not the case...!!!
From Hemmings Daily Tech 101-Octane; The facts and fiction.
Because higher octane gas burns slower, it is more resistant to knock when subjected to higher RPM and cylinder pressures. Compression ratios also factor into cylinder pressures. Higher ratios cause higher cylinder pressures and therefore cause the engine to be more susceptible to pre-detonation or knock.
Link what you want...the explanation is wrong...
It IS, as I've posted, the resistance to autoignition.
Gasoline flame speed is virtually identical regardless of octane rating.
First we need to discuss knock...
Knock is traditionally referred to as "end gas autoignition"
End gas being the gasses at the ends of the combustion chamber, remote from the spark initiation point... (note, ring land failure...that's the last bit to get burned).
Increasing the turbulence in a combustion chamber actually INCREASES the burn speed, up to 10%, and that is one of the ways in which knock is reduced...so flame speed is NOT resistance to knock.
When the spark initiated a flame, the flame front progresses away from the spark at the local flame speed. The pressure in the chamber increases, and that pressure increase is transmitted through the chamber at the local speed of sound (KRT^0.5), K and R being constants, T being temperature in Kelvins (Celsius plus 273))...so the gasses at the end of the combustion process are increasing rapidly in pressure, and as per your bicycle pump experience, this makes them hot also).
If the pressure and temperature rise high enough for the fuel, the fuel/air … in the END GAS … autoigites (end gas autoignition) … and as it's an homogeneous mixture, it tends to all go off at once...with a bang...and all ahead of the flame front.
This event takes place all at the end of the chamber away from the flame front....if the flame had burned smoothly through, there would be no pressure spike.
"Octane rating" is the resistance to this end gas spontaneously "exploding"
Octane requirements near the plug are nil...further out, in the flame front proper, not much either...at the end gas phase...that's where you need the octane.
How it's measured ?
Iso-octane (2,2,4, trimethylpentane) is defined as 100, n-heptane is defined as zero. THe octane rating is the percentage of Isooctane and N-heptane that brackets the performance of a test fuel in a test engine under the various test methods.
QED...it has NOTHING to do with burn rate.
Quoting junk science and defending it to the death is becoming a major part of this board these days... I'm getting over it.
Knock is traditionally referred to as "end gas autoignition"
End gas being the gasses at the ends of the combustion chamber, remote from the spark initiation point... (note, ring land failure...that's the last bit to get burned).
Increasing the turbulence in a combustion chamber actually INCREASES the burn speed, up to 10%, and that is one of the ways in which knock is reduced...so flame speed is NOT resistance to knock.
When the spark initiated a flame, the flame front progresses away from the spark at the local flame speed. The pressure in the chamber increases, and that pressure increase is transmitted through the chamber at the local speed of sound (KRT^0.5), K and R being constants, T being temperature in Kelvins (Celsius plus 273))...so the gasses at the end of the combustion process are increasing rapidly in pressure, and as per your bicycle pump experience, this makes them hot also).
If the pressure and temperature rise high enough for the fuel, the fuel/air … in the END GAS … autoigites (end gas autoignition) … and as it's an homogeneous mixture, it tends to all go off at once...with a bang...and all ahead of the flame front.
This event takes place all at the end of the chamber away from the flame front....if the flame had burned smoothly through, there would be no pressure spike.
"Octane rating" is the resistance to this end gas spontaneously "exploding"
Octane requirements near the plug are nil...further out, in the flame front proper, not much either...at the end gas phase...that's where you need the octane.
How it's measured ?
Iso-octane (2,2,4, trimethylpentane) is defined as 100, n-heptane is defined as zero. THe octane rating is the percentage of Isooctane and N-heptane that brackets the performance of a test fuel in a test engine under the various test methods.
QED...it has NOTHING to do with burn rate.
Quoting junk science and defending it to the death is becoming a major part of this board these days... I'm getting over it.
I read or was told the theory about higher octane burning slower probably around 17 years ago when I was 18 and I always assumed it was true. So if the higher octane has no ethanol, increasing its energy content, plus it doesn't ping in my ancient 305 small block Chevy, then there is no reason not to use it. I used to go through a tank every few days because of my long highway commute. Now with my short drive to work a 20 gal tank of fuel can last 2 weeks usually so I'm worried about the ethanol sitting around and corroding the insides of my carburetor.
Originally Posted by StevieC
I put the 91 octane in from low fuel light tonight at esso and it's stumbling worse than the Petro 91 so I'm going to run this tank out and try Esso 87 for a full tank.
I did run around after the fill with a couple hot starts.
Timing did advance with the 91 octane over the 87 previously by about 4 degrees or so
That's interesting and very unexpected especially given the thorough explanation that higher octane doesn't actually burn slower. The only real difference is extra timing so that seems to be the only factor that could cause the stumbling?
I know with my caprice, when I advance the timing a little more than where I have it now (by rotating the distributor) I get a little stumble at idle. With the timing set where it is now it idles smooth as glass regardless of what fuel I run in it. 87 octane I can't remember where I bought it was pinging noticeably (noticeable to me but not loud enough to be noticed by someone who doesn't know cars) and when I spiked it with 94 octane Sunoco it was almost gone. Then a full tank of Esso 91 and it's completely gone. Otherwise it seems to run the same.
I put the 91 octane in from low fuel light tonight at esso and it's stumbling worse than the Petro 91 so I'm going to run this tank out and try Esso 87 for a full tank.
I did run around after the fill with a couple hot starts.
Timing did advance with the 91 octane over the 87 previously by about 4 degrees or so
That's interesting and very unexpected especially given the thorough explanation that higher octane doesn't actually burn slower. The only real difference is extra timing so that seems to be the only factor that could cause the stumbling?
I know with my caprice, when I advance the timing a little more than where I have it now (by rotating the distributor) I get a little stumble at idle. With the timing set where it is now it idles smooth as glass regardless of what fuel I run in it. 87 octane I can't remember where I bought it was pinging noticeably (noticeable to me but not loud enough to be noticed by someone who doesn't know cars) and when I spiked it with 94 octane Sunoco it was almost gone. Then a full tank of Esso 91 and it's completely gone. Otherwise it seems to run the same.
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