Higher octane cleans more from hotter burning?

[addyguy]

I know that higher level of gas (mid-grade, premium) often have higher levels of detergent in them bc they are marketed as 'premium' products. As such, they will clean engines better as a matter of course.

BUT, higher octane gas also (I think) burns hotter than lower octane gas, bc it is designed to resist pre-ignition, and be a bit 'harder' to ignite.

So, will running a higher octane gas result in a cleaner engine just bc the combustion will be hotter, and deposits will be less able to from?

I live and do short trips around a small town running 87 regularly. Once every two weeks like clockwork, I do a 180-200 mile round-trip highway run to the city I used to live in.

I usually run my gas down, and fill up just before this road trip. Was thinking of filling with super-premium 93 'Magnum' from Stinsons (local fuel supplier here) just before the trip.

Will I see a 'cleaning' benefit from this?

 

[thastinger]

Regardless of the gasoline octane rating, the stoichiometric ratio of the engine remains 14.7:1 and the volumetric efficiency of the engine also remains the same as it was, hence BTU output remains the same, hence combustion chamber temperature remains the same.

 

[ford46guy]

premium gas in a car that don't call for it won't do a single thing. If it makes you believe it does, go for it.

Even in a premium speced car it will allow for the correct timing advance for maximum power, without detonation. If there is knocking, the PCM simply retards timing.

Better off taking the extra money and buying a bottle of Tectron or high PEA cleaner.

 

[Lyman]

I have no idea why people think higher octane gas burns hotter. It's just the opposite. I hear this a lot from different people. Do your Homework!

 

[kschachn]

Nothing quite like the mythology and incorrect information that surrounds the octane rating of a gasoline. The only difference between them is the resistance to detonation (actually spontaneous ignition) which comes in handy with higher compression ratios. If your engine is able to alter the timing and take advantage of a high compression ratio then it will be more efficient with a higher octane fuel. Otherwise there will be no difference, it will neither help nor harm. Combustion temperature is not correlated to the octane rating, it is determined by the chemical constituents in the mixture. You can do more to influence combustion temperatures by changing brand than you can do by changing the octane rating. If a particular brand has a higher detergent level in their high octane fuel then that may or may not be helpful but it is unrelated to the actual octane rating of the fuel.

It can get more complicated because there is more than one way to influence the apparent octane rating of gasoline, but you don't know what that is just based on the rating.

https://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=967599

 

[PandaBear]

It means you can increase compression / advance timing more aggressively without knock.

 

[kschachn]

Originally Posted by PandaBear
It means you can increase compression / advance timing more aggressively without knock.

Which is only useful if your engine can take advantage of it, or if you are designing one in the first place.

 

[NO2]

In the old days they used to add more injector cleaner to premium. Now they use the same amount in most gas, and DI engines get dirty no matter what you do.

 

[barryh]

Originally Posted by thastinger
Regardless of the gasoline octane rating, the stoichiometric ratio of the engine remains 14.7:1 and the volumetric efficiency of the engine also remains the same as it was, hence BTU output remains the same, hence combustion chamber temperature remains the same.


There is one other variable that may change. In the right engine ignition advance will increase producing higher peak combustion pressure and higher peak combustion temperature but lower exhaust gas temperature.

 

[dailydriver]

Originally Posted by kschachn
Originally Posted by PandaBear
It means you can increase compression / advance timing more aggressively without knock.

Which is only useful if your engine can take advantage of it, or if you are designing one in the first place.


...or if you (or an accomplished tuner) are able to write an aftermarket tune into your car's ECM to extend the overly 'safe' factory set parameters out a little bit for more power...

Of course, this WILL void your power train warranty, especially if you own a Ford, which has that ECM re-write/flash COUNTER built into it's function, which enables the dealership/Ford warranty police to tell if there was EVER a tune installed. []

 

[walterjay]

I know that in air cooled engines premium will often run cooler than regular, Not sure why. A guy had a Volkswagen with head temperature guages. In the summer months he ran premium because the engine heads were 10 degrees cooler with it.

 

[Ded Mazai]

Originally Posted by thastinger
Regardless of the gasoline octane rating, the stoichiometric ratio of the engine remains 14.7:1 and the volumetric efficiency of the engine also remains the same as it was, hence BTU output remains the same, hence combustion chamber temperature remains the same.


Combustion temperature is not constant during the combustion and also it depends on the ignition timing advancement. Retarding the timing leads to incomplete burning and higher exhaust gas temperatures, higher piston, rings, exhaust valves temperatures. Retarding leads to more deposits. Using 91 gas in place of 87 will not do any good either if the engine runs at the correct timing on 87 gas. Actually it may make things worse because to burn higher octane gas efficiently you need to compress it more. Otherwise, you may get more deposits on 91 gas. The best practice is to run the lowest octane possible which doesn't produce knocking. Usually it is the recommended gas by the manufacturer.

 

[Ded Mazai]

Originally Posted by addyguy


Will I see a 'cleaning' benefit from this?



Not likely. You may see some benefits from using ethanol free Shell 91 or Shell 89 with only 5% of ethanol. Depends on your engine octane requirements.

 

[dave1251]

Originally Posted by NO2
In the old days they used to add more injector cleaner to premium. Now they use the same amount in most gas, and DI engines get dirty no matter what you do.


Premium gets more because it's a "dirtier" fuel and needs higher concentrations to prevent buildup.

 

[tiger862]

Contrary to most beliefs better octane is better for vehicles. Why don't manufacturers recommend it? People today don't want to spend the money on fuel. All manufacturers are trying to get 91 octane fuel normal as vehicles get better mileage and a more efficient burn with cleaner emissions. I ran 89 in last 3 vehicles with 2 that didn't have flex fuel. All of my driving up until this year was city driving with pipes were clean, plugs lasted longer and engine was quieter on acceleration. On my flex fuel vehicle it is smoother and quieter. Neither got an improvement of mpg but with higher grade of fuel I am sure it helps getting better mileage out of engine.

 

[Shannow]

Originally Posted by Blkstanger
I have no idea why people think higher octane gas burns hotter. It's just the opposite. I hear this a lot from different people. Do your Homework!


Nope, it's not "just the opposite"...there's no difference.

 

[y_p_w]

Originally Posted by dave1251
Originally Posted by NO2
In the old days they used to add more injector cleaner to premium. Now they use the same amount in most gas, and DI engines get dirty no matter what you do.


Premium gets more because it's a "dirtier" fuel and needs higher concentrations to prevent buildup.

Not these days. It used to be that the typical means of blending for high octane rating was to use more aromatics, but these days the technologies are far different with reformulated gas requirements. You can look up the requirements, and I don't think there's really anything other than a performance requirement for the amount of deposits. And since base fuel is a commodity, it's generally assumed that the differences in the base fuel aren't enough to make much of a difference compared to the detergent performance.

 

[y_p_w]

Originally Posted by tiger862
Contrary to most beliefs better octane is better for vehicles. Why don't manufacturers recommend it? People today don't want to spend the money on fuel. All manufacturers are trying to get 91 octane fuel normal as vehicles get better mileage and a more efficient burn with cleaner emissions. I ran 89 in last 3 vehicles with 2 that didn't have flex fuel. All of my driving up until this year was city driving with pipes were clean, plugs lasted longer and engine was quieter on acceleration. On my flex fuel vehicle it is smoother and quieter. Neither got an improvement of mpg but with higher grade of fuel I am sure it helps getting better mileage out of engine.

If you've got a flex fuel vehicle, it's probably capable of extremely high timing advance to take advantage of the high octane rating (about 108 AKI) of E85.

 

[Mad_Hatter]

If it's a TT fuel, ALL GRADES must have the minimum detergent levels set by Top Tier. Whether or not the "premium" brand you're buying has more detergents than the TT minimum is up to the fuel brand.

76 (ConocoPhillips) for example advertises on their website that all grades have more than the TT minimum (and 3x the EPA minimum). For 76 at least, there is ZERO difference in the detergent levels between the 3 grades. I believe Chevron is the same. All 3 grades get the same amount of Techron.