HPL NO VII 10w-20 “EURO” VOA

[Bonz]

Hey thanks for the reply. That's exactly I said. Higher octane than the vehicle was the designed for slows down the combustion process. When something happens later than it should such as gas igniting, that is slowing down the combustion process. Therefore the flame front is not optimized for what the engine is designed for. When gas burns at the same rate, higher octane finishes burning later because it started burning later and can cause issues with carbon on exhaust valves.

 

[Hohn]

Hey thanks for the reply. That's exactly I said. Higher octane than the vehicle was the designed for slows down the combustion process. When something happens later than it should such as gas igniting, that is slowing down the combustion process. Therefore the flame front is not optimized for what the engine is designed for. When gas burns at the same rate, higher octane finishes burning later because it started burning later and can cause issues with carbon on exhaust valves.

No, higher octane doesn’t slow down the combustion process. The same amount of fuel burns in the same amount of time.

The effect of higher octane is to raise the amount of energy required for autoignition. And since the spark exceeds the energy (by far) for both octane ratings, the combustion event initiates at the same time and propagates at the same rate.

If higher octane “slowed down” combustion, it would raise exhaust gas temperatures. But it doesn’t do that. Because it’s not slowing down the combustion process. It’s raising the threshold required to START that process.

This is a subtle but important distinction.

 

[Bonz]

Higher octane allows gasoline to resist ignition, if it burns in the same amount of time once it ignites as regular gasoline, than combustion of the gasoline ends later then the engine was designed for. You're saying the same thing I am. Just trying to make sure you understand that. It's a known fact running high octane gas in engines designed for regular gasoline is not a performance benefit and can cause the issues I have been sharing since my first post.

 

[Hohn]

Slowing down the combustion process with higher octane does lead to exhaust valve deposits down the road. It produces less power as well typically, as the flame front isn't optimized for what the car is designed for.

93 octane doesn't have slower combustion, once ignited. It just has more resistance to autoignition-- a higher activation energy is required.

That said, my main reason to run Shell premium right now is antiwear and detergency and has nothing really to do with octane.

Hey thanks for the reply. That's exactly I said. Higher octane than the vehicle was the designed for slows down the combustion process. When something happens later than it should such as gas igniting, that is slowing down the combustion process. Therefore the flame front is not optimized for what the engine is designed for. When gas burns at the same rate, higher octane finishes burning later because it started burning later and can cause issues with carbon on exhaust valves.

No, higher octane doesn’t slow down the combustion process. The same amount of fuel burns in the same amount of time.

Higher octane allows gasoline to resist ignition, if it burns in the same amount of time once it ignites as regular gasoline, than combustion of the gasoline ends later then the engine was designed for.

No, this is NOT what I was saying. Higher octane resists AUTOignition. It resists ignition due to cylinder pressure. It does NOT resist spark ignition NOR burn slower once lighted.

You're saying the same thing I am. Just trying to make sure you understand that. It's a known fact running high octane gas in engines designed for regular gasoline is not a performance benefit and can cause the issues I have been sharing since my first post.

We're not saying the same thing, and if you still think that, then I don't know how to help you since English is the only language I know. It is NOT a known fact that higher octane than specified causes carbon on the exhaust valves or any of "issues (you) have been sharing since your first post.

Higher octane that specified may have no particular benefits for combustion (sufficiency is sufficiency, after all), but it absolutely has no harm whatsoever. There is no MPG penalty, there is no difference in flame speed. The cutoff ratio is the same, the energy content is essentially the same, the equivalence ratio is the same.

The reason this myth is so widely held is that Google tells you premium fuel burns slower. Because Google and AI don't know what is true, they only know what is popularly believed to be true. Think about that. So if Motor Trend publishes an article restating the myth that premium fuel "burn slower", then Google ranks it higher, and it becomes self-reinforcing. People reference that and next thing you know it becomes something "everyone knows" even though it is known to science to be false.


I'll recommend a text for you if you wish to better understand combustion dynamics. I have referred to my personal copy in the course of correcting your error.

https://www.amazon.com/Introduction-Combustion-Concepts-Applications/dp/0073380199/ref=sr_1_6?sr=8-6

 

[Bonz]

What I do agree is one of us is not correct in what they're talking about. I'll leave that up to the collective to decide since this seems to be a one versus one debate right now.

A higher octane gas is more tolerant to auto ignition, it is more tolerant to spark ignition as well. Auto ignition is caused by higher temperatures and resisting higher temperatures means until the spark reaches a higher temperature the gas won't as easily ignite. The spark doesn't begin at its optimum temperature, it builds and grows to a peak.

It is a fact higher octane gas in engines not designed for it can create carbon fouling on exhaust valves because the mixture is burning at a different point in the combustion cycle than regular gasoline.

As a result, that burn continues albeit in the same time as regular gasoline but later in the process, when the exhaust valves are beginning to open and combustion is not fully complete. Ergo the buildup of carbon from that gas finishing burning as it exits the engine.

When talking in terms of thousands of rpm, it doesn't take much to throw off the timing of the gas burning in the cylinder at the optimal time of the compression stroke where combustion begins before top dead center.

Performance of the engine is compromised. It may not be by much but it's what happens.

 

[fitrucker]

What causes carbon build up is timing retard for the loads you're trying to run. The cylinder head gets hotter. I've run premium in most of my cars since I could get it with no issues. Since 1994 the obd2 ECU had 2 maps. High and low octane. I've always got 6 or more better mpg per gallon with premium. The new engines are basically a variable compression air pump. Engines are not tuned for only one fuel but a range of gasoline which regular is considered the lowest and the engine management is constantly looking for best power using the least amount of fuel.

 

[SubieRubyRoo]

What causes carbon build up is timing retard for the loads you're trying to run. The cylinder head gets hotter. I've run premium in most of my cars since I could get it with no issues. Since 1994 the obd2 ECU had 2 maps. High and low octane. I've always got 6 or more better mpg per gallon with premium. The new engines are basically a variable compression air pump. Engines are not tuned for only one fuel but a range of gasoline which regular is considered the lowest and the engine management is constantly looking for best power using the least amount of fuel.

6mpg or more running premium? Would love to see some independent data verifying that. You must have magic fuel.

 

[fitrucker]

6mpg or more running premium? Would love to see some independent data verifying that. You must have magic fuel.

I have pictures of my old civic with the r18 with over 600 mile range and in the upper 40s mpg. I should not of quoted mpg numbers without independent data. But from what I've seen there is improvement but it's dependant on conditions and loads. Obviously I do a lot of hwy driving.

 

[SubieRubyRoo]

I have pictures of my old civic with the r18 with over 600 mile range and in the upper 40s mpg. I should not of quoted mpg numbers without independent data. But from what I've seen there is improvement but it's dependant on conditions and loads. Obviously I do a lot of hwy driving.

No offense but I'm pretty certain it wasn't the fuel. My wife had one of those Civics when we first met, and on a road trip to Gatlinburg and back I averaged over 46mpg on 87. Just as a validated point that not every manufacturer leaves power on the table, here's a quote from Cobb Tuning (and you know they wouldn't say this if it wasn't true because they're basically saying, "Why buy our tune? There's no power to gain...") on the FA24 turbo 2.4L engine in Subarus these days, rated at 260HP/277TQ:

During development, we discovered that Subaru truly calibrated the ECU to use an 87 octane fuel and testing with higher octane fuel on the factory calibration did not impact the overall power of the engine, though it did clean up occasional minor knock events.

OTOH the 3.5EB is well-known to advertise only 87 octane is needed, but has been proven repeatedly to make around mid-20s additional HP when the tank is full of 93 and has had time to adjust. Some engines have inherent design factors which limit dynamic compression which is a big factor in how much octane is required.

 

[Jetronic]

What I do agree is one of us is not correct in what they're talking about. I'll leave that up to the collective to decide since this seems to be a one versus one debate right now.

A higher octane gas is more tolerant to auto ignition, it is more tolerant to spark ignition as well. Auto ignition is caused by higher temperatures and resisting higher temperatures means until the spark reaches a higher temperature the gas won't as easily ignite. The spark doesn't begin at its optimum temperature, it builds and grows to a peak.

It is a fact higher octane gas in engines not designed for it can create carbon fouling on exhaust valves because the mixture is burning at a different point in the combustion cycle than regular gasoline.

As a result, that burn continues albeit in the same time as regular gasoline but later in the process, when the exhaust valves are beginning to open and combustion is not fully complete. Ergo the buildup of carbon from that gas finishing burning as it exits the engine.

When talking in terms of thousands of rpm, it doesn't take much to throw off the timing of the gas burning in the cylinder at the optimal time of the compression stroke where combustion begins before top dead center.

Performance of the engine is compromised. It may not be by much but it's what happens.

the start of the burn is solely determined by the spark plug igniting, in a spark engine that runs normal. That means higher octane fuel finishes it's burn at the same time, or earlier, as low octane fuel. Possibly earlier as you have less chance of ignition retardation resulting from detection of knock in previos revolutions of the engine.

 

[fitrucker]

No offense taken, just do you. I have 2 Honda's and one is regular only which is a direct injection except when towing. The other one a Honda Civic k20c2 I use premium most of the time. I get better throttle response and lower loads for the the same rpm. Like I said it's about conditions and it's tuned for a range of octane from 90 to 100 in general. It's like this otherwise it would not run right because conditions change. If you monitor fuel trims it will stabilize after corrections and read the same for what ever fuel. Timing goes up and down with a wider variation then premium which is more consistent.

 

[Hohn]

B

Thread 'FLAME SPEED DOES NOT CORRESPOND TO OCTANE RATING!!'

Aug 17, 2007

There used to be a great tech article on Chevron's website, but it's been gone a while. In its absence, there is a good FAQ which covers the same stuff and more available at http://www.faqs.org/faqs/autos/gasoline-faq/

A small excerpt from Part 3:

Quote:

---

6.3 What fuel property does the Octane Rating measure?

The fuel property the octane ratings measure is the ability of the unburnt
end gases to spontaneously ignite under the specified test conditions.
Within the chemical structure of the fuel is the ability to withstand
pre-flame conditions without decomposing into...

• bulwnkl
• Replies: 3
• Forum: Mechanical/Maintenance Forum

....2. The flame speed of the conventionally ignited mixture, this should be
evident from the similarities of the two reference hydrocarbons.
Although flame speed does play a minor part, there are many other factors
that are far more important. ( such as compression ratio, stoichiometry,
combustion chamber shape, chemical structure of the fuel, presence of
antiknock additives, number and position of spark plugs, turbulence etc.)
Flame speed does not correlate with octane.

Another source:
https://www.imoc.co.uk/technical/article/octane.htm

 

[RDY4WAR]

What I do agree is one of us is not correct in what they're talking about. I'll leave that up to the collective to decide since this seems to be a one versus one debate right now.

A higher octane gas is more tolerant to auto ignition, it is more tolerant to spark ignition as well. Auto ignition is caused by higher temperatures and resisting higher temperatures means until the spark reaches a higher temperature the gas won't as easily ignite. The spark doesn't begin at its optimum temperature, it builds and grows to a peak.

It is a fact higher octane gas in engines not designed for it can create carbon fouling on exhaust valves because the mixture is burning at a different point in the combustion cycle than regular gasoline.

As a result, that burn continues albeit in the same time as regular gasoline but later in the process, when the exhaust valves are beginning to open and combustion is not fully complete. Ergo the buildup of carbon from that gas finishing burning as it exits the engine.

When talking in terms of thousands of rpm, it doesn't take much to throw off the timing of the gas burning in the cylinder at the optimal time of the compression stroke where combustion begins before top dead center.

Performance of the engine is compromised. It may not be by much but it's what happens.

The difference in ignition point between regular 87 and Sunoco SR18 (120 octane) is extremely small. At 7000 rpm, it's less than 1° crank timing difference.

 

[Bonz]

Good discussion. I can see there is merit to more modern vehicles with fuel injection and electronic timing controls being less prone or not affected by issues with carbon buildup. I have experience back in the day with carbureted vehicles with more rudimentary ignition systems and it was a fact running high octane when it wasn't needed would carbon up the back of exhaust valves. I have to say with humility there's room for both, and different experiences.

 

[SubieRubyRoo]

The difference in ignition point between regular 87 and Sunoco SR18 (120 octane) is extremely small. At 7000 rpm, it's less than 1° crank timing difference.

OMG! End of the world for ignition retardation! That’s like .000000000005 seconds too late; we’ve crossed both streams and the Rubicon and it’s going to cause the Flux Capacitor to blow!! Great Scott!!