Does octane matter that much?

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Faster burning fuels tend to have higher octane numbers as detonation takes time to happen. The faster you can complete combustion the better in regards to preventing detonation.
BTX are great octane boosters, however there use is no longer a thing in motor gas due to the EPA. All modern refineries have units that remove aromatics.
The facility I work at makes 88 octane gas from its crude unit, 90 from its FCC, 93 from its alky. It's all about blending quality with garbage so you can sell every drop of hydro carbon you refine.
And yes ethanol is all of the things you mentioned. Absolute crap. Incidentally it's also why gasoline is expensive in relation to crude at the moment. Thank Biden and RINS.
 
I don't think octane plays as much a role as the quality of the fuel itself. Testing 93 pump to VP U4.4 race fuel (105 octane) I can tell a slight difference in performance. Is it worth the price of race fuel vs pump fuel, no. As for hard starting or sluggish performance I have had good luck using Fix It Fuel. A tank or two of Fix It Fuel seems to clear the fuel system and carb out real nice.
 
Jonny has this pretty close.
Essentially correct. The higher the octane rating, the less likely the fuel will detonate and, instead, will burn quickly. In the ICE, the "power stroke" ideally wants to push the piston down with a rapid burn/combustion...and not explode. The explosion or detonation is very harmful to the engine and power is significantly reduced. As stated above, the engines with a higher compression ratio typically need higher octane fuels to avoid detonation. Higher performance engines really need higher octane levels. Folks often put "premium" in the fuel tank of their standard-performance engine thinking that it is better and that the engine will run better. Well, maybe and maybe not. If the engine is not designed for the higher octane fuels, the slower burning high-octane fuel may actually produce slightly less power.

In my quite high performance dirt bike motor I needed at least 105 Octane or it would vibrate. High Octane fuel burns very slow allowing for dramatic increase in timing advance. High Octane fuel can be ignited far in advance of TDC which allows for the combustion to take place over a longer period of the stroke which increases overall performance. Alcohol has a pretty even 110 Octane rating which is a common additive allowing for low grade fuel thinking it is higher than it is. Low grade fuel burns very rapidly not allowing for much timing advance. A fast burning fuel tends to burn for a very short period of time not taking full advantage of the entire stroke. What does this have to do with chain saw operation well pretty much nothing. Chainsaw motors are low performance low RPM low compression but plenty of fun along with very long lives as compared to race motors. If you run a saw at higher elevations you even need less octane or much more timing advance. Thanks
 
Ted Jenkins said:
Jonny has this pretty close.
Essentially correct. The higher the octane rating, the less likely the fuel will detonate and, instead, will burn quickly. In the ICE, the "power stroke" ideally wants to push the piston down with a rapid burn/combustion...and not explode. The explosion or detonation is very harmful to the engine and power is significantly reduced. As stated above, the engines with a higher compression ratio typically need higher octane fuels to avoid detonation. Higher performance engines really need higher octane levels. Folks often put "premium" in the fuel tank of their standard-performance engine thinking that it is better and that the engine will run better. Well, maybe and maybe not. If the engine is not designed for the higher octane fuels, the slower burning high-octane fuel may actually produce slightly less power.

In my quite high performance dirt bike motor I needed at least 105 Octane or it would vibrate. High Octane fuel burns very slow allowing for dramatic increase in timing advance. High Octane fuel can be ignited far in advance of TDC which allows for the combustion to take place over a longer period of the stroke which increases overall performance. Alcohol has a pretty even 110 Octane rating which is a common additive allowing for low grade fuel thinking it is higher than it is. Low grade fuel burns very rapidly not allowing for much timing advance. A fast burning fuel tends to burn for a very short period of time not taking full advantage of the entire stroke. What does this have to do with chain saw operation well pretty much nothing. Chainsaw motors are low performance low RPM low compression but plenty of fun along with very long lives as compared to race motors. If you run a saw at higher elevations you even need less octane or much more timing advance. Thanks
Click to expand...
High octane fuel does not burn slower. Burning slow hurts anti knock characteristics, not improve them.
 
lower octane gas has a longer burn duration than higher octane gas. Higher octane burns for less duration and is more resistant to preignition. Detonation is a symptom of preignition. If the carb was adjusted to the edge using premium fuel and low octane fuel was substituted you can have preignition problems and overheat the saw. Check your plug for electrode wear/increased gap and over heating.
 
cookies said:
lower octane gas has a longer burn duration than higher octane gas. Higher octane burns for less duration and is more resistant to preignition. Detonation is a symptom of preignition. If the carb was adjusted to the edge using premium fuel and low octane fuel was substituted you can have preignition problems and overheat the saw. Check your plug for electrode wear/increased gap and over heating.
Click to expand...
Low octane gas may indeed burn slower than high Octane gas, but that's not absolute. When talking pump gas it's safe to assume burn speed varies more by batch than it does by octane.
And detonation can and often does occur independently of pre ignition. However an engine that has pre ignition present puts alot of heat into the piston and head, which really sets the wheels in motion for detonation to start happening.
 
Burn speed is not related to octane. They are two different properties of a fuel and can be adjusted independently. You can have high octane and fast burn speed. Gasoline is not a single hydrocarbon like octane or butane or ethanol. it is instead a blend that is around c7h14. pump gas is a blend of what’s cheap that can meet regulations and be roughly c7h14. It changes depending on feed stock and market regulations ie time of year or local environmental regs. race gas is usually the same components each time so it doesn’t vary and you can get know performance that doesn’t change. Need a fuel with high octane and fast flame speed, you can buy that. Although the formulas can be changed as vp recently did which caused a lot of issues with bean oil on one fuel. I expect 100ll and canned fuels are also more controlled than pump gas So they are more consistent.
 
Slotracer577 said:
Burn speed is not related to octane. They are two different properties of a fuel and can be adjusted independently. You can have high octane and fast burn speed. Gasoline is not a single hydrocarbon like octane or butane or ethanol. it is instead a blend that is around c7h14. pump gas is a blend of what’s cheap that can meet regulations and be roughly c7h14. It changes depending on feed stock and market regulations ie time of year or local environmental regs. race gas is usually the same components each time so it doesn’t vary and you can get know performance that doesn’t change. Need a fuel with high octane and fast flame speed, you can buy that. Although the formulas can be changed as vp recently did which caused a lot of issues with bean oil on one fuel. I expect 100ll and canned fuels are also more controlled than pump gas So they are more consistent.
Click to expand...
That is correct by an large. The bigger reason for octane rating is the fuels ability to be in a combustion chamber and not ignite before it is supposed to which causes knock. If the fuel ignites too far in advance of TDC the fuel pushes down on the piston before the power stroke robbing HP and vibration. Too much knock will destroy many engines. As far as chain saws they do not need much to be happy. Thanks
 
I'll say it again octane is not as important as the quality of the fuel. Every brand has there own additives and quality control that have much more to do with how a fuel preforms. Octane ratings are posted to give you an idea to what application you need it for, if you take the time to read and understand what octane is. Octane is the flash point, period.
 
What are you meaning by flash point? The standard use of the term is the temperature at which flammable vapors are produced. Gasoline is at -40 or so regardless of octane level, kerosene at 105, diesel is in a similar range as kero. Ethanol is around 70 deg and goes up as more water is a part of the mix.
 
OM617YOTA said:
What are you meaning by flash point? The standard use of the term is the temperature at which flammable vapors are produced. Gasoline is at -40 or so regardless of octane level, kerosene at 105, diesel is in a similar range as kero. Ethanol is around 70 deg and goes up as more water is a part of the mix.
Click to expand...
Gas will ignite by compression alone without a spark. The higher the octane the more compression it takes to ignite the fuel. Thats why high octane is used in high compression motors to prevent pre ignition form compression alone. It delays ignition till the spark plug can ignite the fuel at the proper point in the stroke.
 
sb47 said:
Gas will ignite by compression alone without a spark. The higher the octane the more compression it takes to ignite the fuel. Thats why high octane is used in high compression motors to prevent pre ignition form compression alone. It delays ignition till the spark plug can ignite the fuel at the proper point in the stroke.
Click to expand...
Thank you, quite aware of all of that.

That's also not what flash point means.
 
I ran some of my VP U4.4 (105) octane in all of my saws at some point just to see what it will do. I can say with confidence that there is a difference in performance over pump gas. By using the felling dogs with pump gas I can easily bog it down and stop the chain. With the VP fuel it takes a lot more force to stop the chain. I have to bear down at least twice as much with the VP fuel to get it to bog down and stop. So yes I can feel a difference from one fuel vs the other. It does not idle or run faster and there is no difference in how it starts. But I can feel a power difference. Is it worth the extra money, no.
 
sb47 said:
I'll say it again octane is not as important as the quality of the fuel. Every brand has there own additives and quality control that have much more to do with how a fuel preforms. Octane ratings are posted to give you an idea to what application you need it for, if you take the time to read and understand what octane is. Octane is the flash point, period.
Click to expand...
Octane rating has zero to with Flashpoint, period...
 
sb47 said:
I ran some of my VP U4.4 (105) octane in all of my saws at some point just to see what it will do. I can say with confidence that there is a difference in performance over pump gas. By using the felling dogs with pump gas I can easily bog it down and stop the chain. With the VP fuel it takes a lot more force to stop the chain. I have to bear down at least twice as much with the VP fuel to get it to bog down and stop. So yes I can feel a difference from one fuel vs the other. It does not idle or run faster and there is no difference in how it starts. But I can feel a power difference. Is it worth the extra money, no.
Click to expand...
That particular fuel is optimized for four cycle engines. Better results can be had with a two cycle specific fuel.
And I am not surprised it felt more powerful as that particular fuel has a decent o2 content.
 
sb47 said:
Gas will ignite by compression alone without a spark. The higher the octane the more compression it takes to ignite the fuel. Thats why high octane is used in high compression motors to prevent pre ignition form compression alone. It delays ignition till the spark plug can ignite the fuel at the proper point in the stroke.
Click to expand...
Octane is a measure of resistance to detonation. Which occurs after the spark plug fires. Pre ignition happens because something in the combustion chamber is glowing red hot and acts as a glow plug. High Octane fuel prevents pre ignition to a degree, by not allowing detonation to happen and the resulting high combustion chamber temps that cause pre ignition.
 

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