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somebody once told me that higher octane also clogs up your lambda sensor less and prolongs the life of your catalytic converter.
is that bs?
is that bs?
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Octane rating...95 & 93 (difference)
- Thread starter Ockie
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Takkies
Well-Known Member
They drive it up here? Not Really
Actually yours is quite a good post, but . .
Not all fuel comes from Durban.
SAPREF (BP & Shell) and PetroSA(Engen) are in Natal. NATREF supplies most of Gauteng and SASOL II & III supply Mpumalanga as far as I know. Still the refineries are stocking their own outlets which means everybody is trucking. Of course that is until the government get their new pipeline sorted out. Watch out for another Arms Deal Debacle
Actually yours is quite a good post, but . .
Not all fuel comes from Durban.
SAPREF (BP & Shell) and PetroSA(Engen) are in Natal. NATREF supplies most of Gauteng and SASOL II & III supply Mpumalanga as far as I know. Still the refineries are stocking their own outlets which means everybody is trucking. Of course that is until the government get their new pipeline sorted out. Watch out for another Arms Deal Debacle
Actually the hicher octane at the coast has to do with the higher atmospheric pressure. As you pointed out, it has to do with a controlled explosion in the cars cylinder.
Fazda
Honorary Master
TOTAL BS!
Higher Octane has absolutely nothing to do with blocking Lambda sensors. Poor quality fuel, yes...octane, no.
OC your Polotjie will love you for giving her an extra couple of numbers there....just imagine, two extra boitjies per cylinder when they are busy doing the cleaning..
OverKill69
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It depends on the vehicle... what it is designed for...
You should get better performance and economy from a higher octane rated fuel.
but...
Some cars, usually with smaller engines, are happy with either fuels. Their "stroke length" and "cylinder compression" are designed in such a way to give a lot of leeway one way or the other... so you won't notice such a big difference. In a small engine, heat transfer isn't too much of an issue and the parts are over designed for the force loads to sustain years and years of abuse. As long as the oil is kept cleanish and the vavle and ignition timing is correct, small 4 cylinder engines can go forever on whatever fuel you put in.
The difference comes in with the larger engines.
Most performance cars are designed with European standards and that includes their emissions standards. The emissions regs is what has shot engine power in the foot... engine manufacturers cannot just shove a huge turbo or supercharger on a huge engine block and crank up the boost till the car breaks records... they have to think about the unburnt hydrocarbons coming out o the car's exhaust.
This literally means UNBURNT PETROL coming out of your exhaust... along with CO2 and CO and that rubbish.
In the old days... they'd just pump more gas into the cylinder, it would ignite, and BANG you're going faster than you were before. WHO CARES IF YOU DON'T BURN ALL THE PETROL THAT WENT IN?
Nowadays, we hug bunnies and worship trees... which is a good thing... because it forced engine manufacturers to make more economical engines.
so... your performance vehicle...
Their design tolerances are a lot narrower. Direct Fuel injection, air mass flow meters, smart cams and programmable fuel management chips now decide on the optimum mix of air and fuel that needs to be delivered into your cylinder to give you the most out of each and every precious drop of fuel.
All those programs and what not all are "assuming" you're using premium grade petroleum.
The difference isn't too great between 95 and 93 octane... but the "regular" standard used to be 87 in South Africa. That would make a very big difference!
Racing fuel, available at your nearest race track is usually 100 or 103... which works great if your car has been designed for those octane levels... I know Kyalami used to sell SASOL 100 and 103... but it wouldn't make your "golf GTI" faster... it would make your tuned, "chiped" car go faster though ;-)
Rule of thumb:
1.6 or smaller - no difference
1.8 with fuel injection - little difference, but ever so slightly better mileage with 95
2.0 and above - differences get quite noticeable.
V6, V8 or larger - Manufacturers recommend ONLY using premium
Turbo or supercharged engine - use only premium
Diesel - use the 50ppm diesel. What they don't tell you is that your eco-green wonder diesel engine in your audi/beamer/merc was designed with low sulfur diesel in mind. The 500ppm diesel WILL mess up your injectors, intake manifold, oil and CAT. One of the selling points on the new diesels are their INSANE service intervals... WELL.. That only works if you use the LOW SULFUR 50ppm diesel. Otherwise, you're gonna break it! SERIAS. you might not see it at 30 000kms... but at 100 000kms, you'll have a cracked head or worse.
You should get better performance and economy from a higher octane rated fuel.
but...
Some cars, usually with smaller engines, are happy with either fuels. Their "stroke length" and "cylinder compression" are designed in such a way to give a lot of leeway one way or the other... so you won't notice such a big difference. In a small engine, heat transfer isn't too much of an issue and the parts are over designed for the force loads to sustain years and years of abuse. As long as the oil is kept cleanish and the vavle and ignition timing is correct, small 4 cylinder engines can go forever on whatever fuel you put in.
The difference comes in with the larger engines.
Most performance cars are designed with European standards and that includes their emissions standards. The emissions regs is what has shot engine power in the foot... engine manufacturers cannot just shove a huge turbo or supercharger on a huge engine block and crank up the boost till the car breaks records... they have to think about the unburnt hydrocarbons coming out o the car's exhaust.
This literally means UNBURNT PETROL coming out of your exhaust... along with CO2 and CO and that rubbish.
In the old days... they'd just pump more gas into the cylinder, it would ignite, and BANG you're going faster than you were before. WHO CARES IF YOU DON'T BURN ALL THE PETROL THAT WENT IN?
Nowadays, we hug bunnies and worship trees... which is a good thing... because it forced engine manufacturers to make more economical engines.
so... your performance vehicle...
Their design tolerances are a lot narrower. Direct Fuel injection, air mass flow meters, smart cams and programmable fuel management chips now decide on the optimum mix of air and fuel that needs to be delivered into your cylinder to give you the most out of each and every precious drop of fuel.
All those programs and what not all are "assuming" you're using premium grade petroleum.
The difference isn't too great between 95 and 93 octane... but the "regular" standard used to be 87 in South Africa. That would make a very big difference!
Racing fuel, available at your nearest race track is usually 100 or 103... which works great if your car has been designed for those octane levels... I know Kyalami used to sell SASOL 100 and 103... but it wouldn't make your "golf GTI" faster... it would make your tuned, "chiped" car go faster though ;-)
Rule of thumb:
1.6 or smaller - no difference
1.8 with fuel injection - little difference, but ever so slightly better mileage with 95
2.0 and above - differences get quite noticeable.
V6, V8 or larger - Manufacturers recommend ONLY using premium
Turbo or supercharged engine - use only premium
Diesel - use the 50ppm diesel. What they don't tell you is that your eco-green wonder diesel engine in your audi/beamer/merc was designed with low sulfur diesel in mind. The 500ppm diesel WILL mess up your injectors, intake manifold, oil and CAT. One of the selling points on the new diesels are their INSANE service intervals... WELL.. That only works if you use the LOW SULFUR 50ppm diesel. Otherwise, you're gonna break it! SERIAS. you might not see it at 30 000kms... but at 100 000kms, you'll have a cracked head or worse.
Ockie
Resident Lead Bender
OC your Polotjie will love you for giving her an extra couple of numbers there....just imagine, two extra boitjies per cylinder when they are busy doing the cleaning..
So would you say I should normally just use 93 but maybe now and then put in some 95 for him? .... yes, I have discovered that my playa is in fact a he!!!! Turns out his tottie pipe was just hidden below the bumper! lol. Me love him!
Fazda
Honorary Master
And here I was convinced that all Playas were she's!
Yes, they love the occasional dash of extra octane...helps keep everything nice and fit inside...and I know that you enjoy well toned bodies...
Ockie
Resident Lead Bender
And here I was convinced that all Playas were she's!
Yes, they love the occasional dash of extra octane...helps keep everything nice and fit inside...and I know that you enjoy well toned bodies...
I do indeed. Thinking of booking my Play into VW again for a tottie extension to make it more obvious he is a boy. Would hate other cars to laugh at him. They can be so cruel!!!! :-(
/BRAINWAVE!!!!!!
What is the octane rating of cheap whiskey???
Thump3r
Well-Known Member
My old 1.8 playa was definitely a gal ... and she really liked the higher octane fuel ... she wasn't chipped but her efficiency did get better by 3km/l
I just wish I could have found a human gal to match her ...
I just wish I could have found a human gal to match her ...
Fazda
Honorary Master
What is the octane rating of cheap whiskey???
About 110 if I remember correctly!
All this talk about octane, it's simple, higher octane fuels require more activation energy to ignite. That means that 93 octane ignites more easily than 95 octane. 95 octane actually contains less energy than 93 octane. It isn't a miracle or cleaner it's just harder to ignite.
The ONLY reason you would want that is to prevent pre-ignition (aka knock), pre-ignition is when pockets of fuel suddenly ignite spontaneously (IE. micro explosions). Engines are designed so that the fuel is burned when the spark plug fires, the burn starts from the spark plug and burns evenly, pre-ignition you have explosions (so it isn't burning it is exploding) that start at random positions in the cylinder.
So in essence pre-ignition is bad. In Turbo engines it is especially bad because turbo engines run on compressed air it is like blowing compressed air on a furnace. Usually a N/A engine can handle quite a bit of pre-ignition but a Turbo engine will burn a hole in the piston, blow a head gasket, etc. by the time you hear it.
The problem is fuel ignites more easily as temperature increases, as fuel ages, etc. So in order to prevent the dreaded pre-ignition from damaging modern engines, a sensor is included called a knock sensor. It is a "microphone" (specifically piezoelectric speaker tuned to a specific frequency) that detects pre-ignition before it can cause damage.
That in turn reduces the ignition timing. HOWEVER that is for fuel injected cars only, and not all of them have knock sensors. FURTHERMORE, ALL, not just some BUT ALL, fuel injected cars have a limit on how much the ignition timing can be reduced or advanced. On production cars the value will certainly never exceed 3 or 4 degrees, even on your most bad ass Ferrari V12 engines.
What it all boils down to: Increasing the ignition timing increases power, it also increases heat exponentially and to a small degree fuel efficiency *may* be increased. Decreasing ignition timing does the opposite UP TO A POINT (at some point you will cause serious damage by decreasing the ignition timing).
Most N/A cars regardless if it is a 2.0, V6 3.0 or I4 1.4 engine won't see much difference between 95 octane VS 93 octane. But engines designed for it like Audi RS4 will see substantial differences. Turbo engines also benefit greatly. Those still have a limit on ignition timing but they were tuned for 95 octane, when running on 93 octane actually means the are running with decreased ignition timings VS normals cars sold in SA which run with a 93 octane map and would run with an increased ignition timing when you use 95 octane. A car tuned with a 93 octane map will probably not make full use of 95 octane because you can usually go a bit higher than just 3 degrees when you move up to 95 octane, depending on engine and the air/fuel mixture.
If you are running an engine at altitude or lower temperatures you actually want fuel that ignites more easily. That is why the high veld runs on 93 octane instead of 95 octane. The air has lower density here and on a carburetor engine the car would have trouble starting with 95 octane when it is cold because the fuel just wouldn't ignite. Even a fuel injected car would have trouble if it got cold enough (especially the older fuel injected cars).
All I can say is: If you think you get benefits from 95 Octane, then make sure you are correct by driving the exact same way, distances, etc. Best would be if you let someone else fill up when doing the experiment, that way it is objective (blind test). Most cars will see little to no benefit.
Lastly, 95 being cleaner than 93 octane is BS. How do you think they get 93 octane? They create a blend, the same for 93 octane, both are equally "dirty/clean". All the fuel is transported to the high veld and then blended for a certain octane.
Ignition timing is the sole reason why increase in octane would be better, 97 octane would probably cause problems even in cars with fuel injected engines, except those designed for high octane. If you ran 97 Octane in the high veld on a N/A engine you'd see a decrease in performance and your engine would run like crap.
The ONLY reason you would want that is to prevent pre-ignition (aka knock), pre-ignition is when pockets of fuel suddenly ignite spontaneously (IE. micro explosions). Engines are designed so that the fuel is burned when the spark plug fires, the burn starts from the spark plug and burns evenly, pre-ignition you have explosions (so it isn't burning it is exploding) that start at random positions in the cylinder.
So in essence pre-ignition is bad. In Turbo engines it is especially bad because turbo engines run on compressed air it is like blowing compressed air on a furnace. Usually a N/A engine can handle quite a bit of pre-ignition but a Turbo engine will burn a hole in the piston, blow a head gasket, etc. by the time you hear it.
The problem is fuel ignites more easily as temperature increases, as fuel ages, etc. So in order to prevent the dreaded pre-ignition from damaging modern engines, a sensor is included called a knock sensor. It is a "microphone" (specifically piezoelectric speaker tuned to a specific frequency) that detects pre-ignition before it can cause damage.
That in turn reduces the ignition timing. HOWEVER that is for fuel injected cars only, and not all of them have knock sensors. FURTHERMORE, ALL, not just some BUT ALL, fuel injected cars have a limit on how much the ignition timing can be reduced or advanced. On production cars the value will certainly never exceed 3 or 4 degrees, even on your most bad ass Ferrari V12 engines.
What it all boils down to: Increasing the ignition timing increases power, it also increases heat exponentially and to a small degree fuel efficiency *may* be increased. Decreasing ignition timing does the opposite UP TO A POINT (at some point you will cause serious damage by decreasing the ignition timing).
Most N/A cars regardless if it is a 2.0, V6 3.0 or I4 1.4 engine won't see much difference between 95 octane VS 93 octane. But engines designed for it like Audi RS4 will see substantial differences. Turbo engines also benefit greatly. Those still have a limit on ignition timing but they were tuned for 95 octane, when running on 93 octane actually means the are running with decreased ignition timings VS normals cars sold in SA which run with a 93 octane map and would run with an increased ignition timing when you use 95 octane. A car tuned with a 93 octane map will probably not make full use of 95 octane because you can usually go a bit higher than just 3 degrees when you move up to 95 octane, depending on engine and the air/fuel mixture.
If you are running an engine at altitude or lower temperatures you actually want fuel that ignites more easily. That is why the high veld runs on 93 octane instead of 95 octane. The air has lower density here and on a carburetor engine the car would have trouble starting with 95 octane when it is cold because the fuel just wouldn't ignite. Even a fuel injected car would have trouble if it got cold enough (especially the older fuel injected cars).
All I can say is: If you think you get benefits from 95 Octane, then make sure you are correct by driving the exact same way, distances, etc. Best would be if you let someone else fill up when doing the experiment, that way it is objective (blind test). Most cars will see little to no benefit.
Lastly, 95 being cleaner than 93 octane is BS. How do you think they get 93 octane? They create a blend, the same for 93 octane, both are equally "dirty/clean". All the fuel is transported to the high veld and then blended for a certain octane.
Ignition timing is the sole reason why increase in octane would be better, 97 octane would probably cause problems even in cars with fuel injected engines, except those designed for high octane. If you ran 97 Octane in the high veld on a N/A engine you'd see a decrease in performance and your engine would run like crap.
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scotty777
...doesn't know
Um, not really, diesel has an octane energy of like 40 or something, and it's pretty tough to light diesel unless you make it into a fine mist...
All that happens when you have a high compression car (like a turbo/supercharged car, or a really high performance car that compresses the shyte out the fuel) is you need to prevent the fuel from igniting when it's being compressed. So you want a more stable fuel for that, like alcohol, but something that loves energy in the form of a flame or spark to ignite it.
You usually should fill the car up with 93, if it's a small car... even my friends dad's E 63 AMG Merc gets filled with 93 octane
. So I really don't think it matters as much as you'd think. Although I think it's all just silly to really care all that much. If my car gets me places, without drinking fuel like a thirsty Irish man in a pub, then I'm happy... besides, if you want more performance, buy a cone air filter, or change the ECU, you'll see much better performance improvements .1) Octane isn't energy. Octane rating is not a measure of energy.
2) Octane is determined by running a known engine configuration with a choice of fuel and slowly increasing the compression ratio, each increase corresponds to an octane rating. Therefore octane is a synthetic measure of a fuels resistance to auto ignition. Octane rating cannot be chemically determined (note a chemical known as octane exists but it alone does not determine the octane rating of a fuel)
3) You confuse activation energy with something as crude as lighting a fuel with a match. Diesel engines operate by injecting Diesel fuel into a hot combustion chamber (eg. hot air) under pressure. The fuel then auto ignites. Therefore Diesel fuel is designed to auto ignite when under pressure.
LOL! Well there is "igniting" and there is igniting. The "igniting" you talk of is called detonation and it is COMPLETELY different from when fuel is ignited by the spark plug
Spark plug burns starting from the tip of the spark plug, detonation the pockets of air explode violently. Therefore you get much higher cylinder pressure and heat from detonation than normal ignition. That is also why Turbo engines absolutely cannot have detonation whereas N/A engines handle it far better.Not entirely true, you could easily ignite diesel fuel with a spark. You see a spark and you think that it isn't significant but in reality the air between the electrode and ground have become super heated. The amount of heat generated is far higher than that generated by a flame. I got this just for you:
Wikipedia said:
Furthermore Petrol, not even 93 octane is combusted completely when you light it with a match, that is why it creates so much black soot.
Depends on the car, that was the point I was trying to make. Most cars it is useless to go higher on octane because the higher octane fuels don't actually have more energy than the lower octane fuels.You usually should fill the car up with 93, if it's a small car... even my friends dad's E 63 AMG Merc gets filled with 93 octane
In fact Alcohol has significantly less energy than gasoline (but it has an octane rating of around 130 RON whereas we get 95 RON at most from our pumps). Therefore if you don't run Alcohol engine (100% ethanol) with high compression ratios (17:1 and higher) you will see a significant decrease in performance and consumption.
Many times ethanol is mixed with fuels to increase their octane, therefore the fuel contains less energy than it had before unless you increase the compression, you loose performance.
Please tell me the last part was a joke? Neither cone filter nor ECU tuning will benefit N/A cars much if at all. Most cars will see a decrease in performance. Cone air filter because the air draws in more hot air. ECU because N/A cars are already well tuned to begin with. Turbo cars, they usually increase the boost, they don't fiddle with the map. Once again proving that without other modifications it is pointless to do any ECU work. Ask any tuner.Although I think it's all just silly to really care all that much. If my car gets me places, without drinking fuel like a thirsty Irish man in a pub, then I'm happy... besides, if you want more performance, buy a cone air filter, or change the ECU, you'll see much better performance improvements
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Actually, scotty, diesel has a cetane number of between 40 and 60. There is some similarity, but cetane numbers are not directly comparable to octane ratings.
Tell your friend's dad he should stop being a cheapskate. You will most definitely notice a difference in a performance vehicle like the E63 AMG - he might just not realise it because he could have been filling up with 93 all this time. Apparently Mercedes-Benz recommends 98 octane at the coast for these models, which is about 95 octane at Reef altitude.
Finally, for better performance I really wouldn't recommend a cone filter, or a ECU reflash on a naturally-aspirated car (no real gains to be had, if any). Good quality exhaust system and proper air intake upgrade would do the trick, but that's derailing the thread...
Tell your friend's dad he should stop being a cheapskate
. You will most definitely notice a difference in a performance vehicle like the E63 AMG - he might just not realise it because he could have been filling up with 93 all this time. Apparently Mercedes-Benz recommends 98 octane at the coast for these models, which is about 95 octane at Reef altitude.Finally, for better performance I really wouldn't recommend a cone filter, or a ECU reflash on a naturally-aspirated car (no real gains to be had, if any). Good quality exhaust system and proper air intake upgrade would do the trick, but that's derailing the thread...
scotty777
...doesn't know
Sorry , not really a car expert . ha ha. I'll wind my neck in next time .
, not really a car expert . ha ha. I'll wind my neck in next time .
sn3rd
Expert Member
I'm mostly in agreement with Gnome, except for the fact that 93 contains more energy than 95. I think it comes down to how you define "more energy"; more per litre?
Octane, in simple terms, will determine how easily fuel will spontaneously ignite. If you remember high school chemistry, an increase in pressure leads to an increase in temperature. As such, during the compression stroke, fuel may spontaneously ignite if the octane is too low. Higher octane fuel will require more compression before spontaneous ignition.
Spontaneous ignition is BAD. Engines are designed for the fuel to ignite at a specific moment. If ignition occurs at other times (knock), all sorts of bad things can happen.
This is not a problem in most normally aspirated engines; compression does not reach levels high enough to trigger spontaneous combustion. However in forced induction (i.e. turbocharged and/or supercharged) engines, peak pressure can reach much higher levels, which can lead to spontaneous combustion. In these cases, a 95 octane fuel will help.
I'm not saying that people who get "better fuel economy" or "better performance" are lying; it's possible that their cars' engines can benefit from this improved tolerance to higher pressures. But it's not the main focus of providing different octane fuels for consumers.
Saying that diesel fuel does not ignite when you take a match to it doesn't prove anything regarding octane; the fuel is still at standard atmospheric pressure.
Octane, in simple terms, will determine how easily fuel will spontaneously ignite. If you remember high school chemistry, an increase in pressure leads to an increase in temperature. As such, during the compression stroke, fuel may spontaneously ignite if the octane is too low. Higher octane fuel will require more compression before spontaneous ignition.
Spontaneous ignition is BAD. Engines are designed for the fuel to ignite at a specific moment. If ignition occurs at other times (knock), all sorts of bad things can happen.
This is not a problem in most normally aspirated engines; compression does not reach levels high enough to trigger spontaneous combustion. However in forced induction (i.e. turbocharged and/or supercharged) engines, peak pressure can reach much higher levels, which can lead to spontaneous combustion. In these cases, a 95 octane fuel will help.
I'm not saying that people who get "better fuel economy" or "better performance" are lying; it's possible that their cars' engines can benefit from this improved tolerance to higher pressures. But it's not the main focus of providing different octane fuels for consumers.
Saying that diesel fuel does not ignite when you take a match to it doesn't prove anything regarding octane; the fuel is still at standard atmospheric pressure.
WILDCARDUT
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Herewith an extraction from the TTV forum:
1) The Rated Octane Number or RON used locally describes the degree to which the fuel resists detonation (it's knock resistance) and is by no means an indication of the energy content of the fuel. So please don't automatically assume that a higher octane fuel will make your car perform better.
2) If your ignition timing can be tuned to within a few degrees of MBT (mean best torque) already, without the occurrence of detonation (using whatever octane fuel you currently use), then changing to a higher octane fuel will do nothing for your cars performance. To the contrary, it can, as many have experienced, lower performance due to the fact that the chemicals added to raise the RON (such as toluene, xylene, methanol etc.) have a lower energy density than locally available petrol.
3) Octane is no substitute for energy content. Tap water, for example, has a RON of a gazillion, but it's not much good for fueling your engine though as its heat of combustion is nil!
So why use a fuel with additives added that raise the octane rating of a fuel while lowering its energy density? To answer that, you need to understand the following:
1) The amount of mechanical energy that your engine can extract from the air-fuel mixture drawn into each combustion chamber is a function of the engines thermal efficiency. For example, if an engine has a thermal efficiency of 50%, then 50% of the heat of combustion goes to turning your wheels, and the other 50% goes out as heat.
2) As a general rule, raising the compression ratio (CR) of an engine raises its thermal efficiency, allowing you to extract more mechanical energy (that's a good thing) from the available heat of combustion.
3) Raising the CR, however, raises the probability of detonation occurring (where the occurrence of detonation is a function of both combustion pressure and temperature).
Hence, under certain circumstances, a legitimate case can be made that a higher CR engine can produce more power at the wheels when running on a higher octane fuel specifically required to avoid detonation despite the fact that the higher octane fuel has a lower energy density than a lower octane fuel.
To put it another way, the loss of performance due to the lower energy density fuel is more than offset by the fact that the higher CR engine (that would otherwise detonate on lower octane fuel) is capable of producing more power at the wheels due to the increase in thermal efficiency due to the higher CR.
FYI, the same is true of forced induction engines where the loss of performance due to the lower energy density fuel is likewise offset by the increase in power at the wheels due to the increase in the intake manifold pressure (which results ultimately in higher combustion pressures and thus increased likelihood of detonation). This was well proven during the era of turbocharged F1 cars which ran on a fuel made up of typically around 80% toluene, which was necessary to run 4-bars of boost.
Take note good people:
Unless your engine falls into the above categories and could genuinely benefit by using a fuel exhibiting greater detonation resistance, thus allowing you to tune your ignition timing closer to MBT, then you will gain nothing/zippo/nil/nix from using a fuel that effectively has a lower energy density.
This is a lesson that many have learned the hard way
1) The Rated Octane Number or RON used locally describes the degree to which the fuel resists detonation (it's knock resistance) and is by no means an indication of the energy content of the fuel. So please don't automatically assume that a higher octane fuel will make your car perform better.
2) If your ignition timing can be tuned to within a few degrees of MBT (mean best torque) already, without the occurrence of detonation (using whatever octane fuel you currently use), then changing to a higher octane fuel will do nothing for your cars performance. To the contrary, it can, as many have experienced, lower performance due to the fact that the chemicals added to raise the RON (such as toluene, xylene, methanol etc.) have a lower energy density than locally available petrol.
3) Octane is no substitute for energy content. Tap water, for example, has a RON of a gazillion, but it's not much good for fueling your engine though as its heat of combustion is nil!
So why use a fuel with additives added that raise the octane rating of a fuel while lowering its energy density? To answer that, you need to understand the following:
1) The amount of mechanical energy that your engine can extract from the air-fuel mixture drawn into each combustion chamber is a function of the engines thermal efficiency. For example, if an engine has a thermal efficiency of 50%, then 50% of the heat of combustion goes to turning your wheels, and the other 50% goes out as heat.
2) As a general rule, raising the compression ratio (CR) of an engine raises its thermal efficiency, allowing you to extract more mechanical energy (that's a good thing) from the available heat of combustion.
3) Raising the CR, however, raises the probability of detonation occurring (where the occurrence of detonation is a function of both combustion pressure and temperature).
Hence, under certain circumstances, a legitimate case can be made that a higher CR engine can produce more power at the wheels when running on a higher octane fuel specifically required to avoid detonation despite the fact that the higher octane fuel has a lower energy density than a lower octane fuel.
To put it another way, the loss of performance due to the lower energy density fuel is more than offset by the fact that the higher CR engine (that would otherwise detonate on lower octane fuel) is capable of producing more power at the wheels due to the increase in thermal efficiency due to the higher CR.
FYI, the same is true of forced induction engines where the loss of performance due to the lower energy density fuel is likewise offset by the increase in power at the wheels due to the increase in the intake manifold pressure (which results ultimately in higher combustion pressures and thus increased likelihood of detonation). This was well proven during the era of turbocharged F1 cars which ran on a fuel made up of typically around 80% toluene, which was necessary to run 4-bars of boost.
Take note good people:
Unless your engine falls into the above categories and could genuinely benefit by using a fuel exhibiting greater detonation resistance, thus allowing you to tune your ignition timing closer to MBT, then you will gain nothing/zippo/nil/nix from using a fuel that effectively has a lower energy density.
This is a lesson that many have learned the hard way
supersunbird
Honorary Master
I tried running my 1.3 Ford Ikon with 95 for a few weeks to get an average. I seemed to get around 40 to 50 km more a tank. Oh well, its too expensive now to make up the difference.
Not a very scientific way to test but who knows why I got it, maybe the traffic conditions were lighter anyway.
Not a very scientific way to test but who knows why I got it, maybe the traffic conditions were lighter anyway.