The Correct Octane Level For Your Car

[junkofdavid2]

These lists seem to suggest that some cars in Thailand actually run better on 91 than on 95:

http://www.shell.com/static/thailand-th/do...List_Jul071.pdf

http://www.shell.com/home/content/thailand...aqs_1130.html#5

As of now, I can confirm that I got 10.3% better mileage on Shell gasohol 91 vs. Shell 95, but that could've been due to other factors such as traffic conditions, change in my driving style, personal bias, etc..

*(The lists above recommend such gasohol 91 for my car instead of 95.)

I'm now testing mileage of PTT regular 91 on my car to see if it's worth the extra 19% higher cost compared to gasohol 91. If it's almost break-even compared to gasohol 91, I'll shift to regular 91 because it's supposedly better for the car engine than gasohol. (Shell doesn't seem to sell regular 91 in most of their stations.)

What car do you use? What gasoline have you been using? What has been your experience with different octane grades?

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Edited March 17, 2009 by junkofdavid2

[dave_boo]

FWIW, in my CBR 150 I noticed a 25% drop in consumption (40 down to 32 km/L) when going from benzine 95 to gasahol 91...

[culicine]

You should use the recommended fuel for your car. Mine is a honda civic 2.0 desigend to run on 91 (though it can run on 91 gasohol). Once an attendant accidentally put in gasohol 95 and it ran poorly and gaver poor consumption. I tested both 91 and 91 gasohol, and the gasohol was more economical. Consumption averaged aboutr 10.5 km/l for the 91 and 9.5 for the gasohol. Perfomance didn't differ that much. You would need to test both types of fuel several times over different driving conditions to test them. I would suggest running the car on gasohol for 5-10 tanks and then comparing to normal for 5-10 tanks. Don't as the engine might need time to adapt to the different fuels (though I'm not sure on this point). Your results might be different from mine.

[indothai]

Driving a '07 CRV, Using Gasohol 91.

Have tried Regular 91.

Have tried Regular 95.

Have tried Gasohol 91.

Have tried Gasohol 95.

Difference between Gasohol and Regular? Regular is more expensive.

Difference between octane grade 91 and 95? 95 is more expensive.

What am i using now? Gasohol 91.

Why am i using Gasohol 91 over other types? Cheaper, almost no difference in performance. Most importantly, manual says so.

Will I continue to use Gasohol 91 in the future? Yes, unless they make the other fuels cheaper.

[junkofdavid2]

I tested both 91 and 91 gasohol, and the gasohol was more economical. Consumption averaged aboutr 10.5 km/l for the 91 and 9.5 for the gasohol.

So you get better mileage on 91 (10.5 km/L) than on gasohol 91 (9.5 km/L). Why is gasohol therefore more economical? Is it because you took into consideration the higher price of gasohol already?

On the other comment above regarding performance... I'm on regular 91 (AlphaX from PTT) right now for testing and the car actually feels "heavy" compared to when I was using either gasohol 91/95. Of course, this could again be personal bias; OR, it could be because in the past I used gasohol 91/95 from Shell and now my regular 91 is from PTT which might have different "qualities" than Shell.

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Edited March 18, 2009 by junkofdavid2

[culicine]

I tested both 91 and 91 gasohol, and the gasohol was more economical. Consumption averaged aboutr 10.5 km/l for the 91 and 9.5 for the gasohol.

So you get better mileage on 91 (10.5 km/L) than on gasohol 91 (9.5 km/L). Why is gasohol therefore more economical? Is it because you took into consideration the higher price of gasohol already?

On the other comment above regarding performance... I'm on regular 91 (AlphaX from PTT) right now for testing and the car actually feels "heavy" compared to when I was using either gasohol 91/95. Of course, this could again be personal bias; OR, it could be because in the past I used gasohol 91/95 from Shell and now my regular 91 is from PTT which might have different "qualities" than Shell.

.

Yes I was also considering the cost difference. When the prices were high, there was a much greater difference in the cost per km. Now the margin is much smaller. I haven't calculated it recently, but I would say I save about 4-5000 baht a year using 91 gasohol (based on 25000 kms a year). So yes its more economical to use 91 gas, but only marginally so in my case.

[onnut]

I can use E20 or regular 91 in My accord I think there is another one I can use as well but did not check the manual. the regular 91 is more expensive and also very hard to find around the area I live, so I tend to use E20 unless I am driving up country because again I cannot seem to find E20 up there. E20 and 91, I cannot feel or notice the difference while driving, both fuels have given me 720 Kilometers to a tank while on long trips with easy driving because her indoors is in the car.

one thing that really annoys me is that every gas station sells different brands even two shell stations could sell different brands, why dont the have some fuels with shell some with jiffy and so on and so on? the ammount of times I have been on the outskirts of Bangkok and I have to drive in and out of gas stations until I find one with the fuel my car can use.

edited for my little rant.

Edited March 18, 2009 by onnut

[PeaceBlondie]

What - you cannot find the right fuel in some little village called Bangkok? Well, come on up to Chiang Mai, where outside the moat, there are lots of stations having lots of fuels for sale. Okay, so any station might be out of one fuel at one time, but I have four choices, and never have to look elsewhere.

I get roughly the same on benzene or ethanol, 91 or 95. I do not shop by brands like Shell. My mileae, carefully measured between full tanks, varies between 32 and 38, but usually I average around 35. Since moving to exurbia and spending more time above 110 kph on the freeway, I have been running about 36 on E10.

If you drive an old carbureted car (like my 1997 Nissan NV) you may only get 9 km/liter. But a new motorcycle is so thrifty that once you exceed 32, you are no longer spending enough to save much more.

[denboy]

FWIW, in my CBR 150 I noticed a 25% drop in consumption (40 down to 32 km/L) when going from benzine 95 to gasahol 91...

I can understand your interest in making comparisons perhaps to satisfy your curiosity. However to make a point.

When engine manufacturers design and built and engine, they literally spent thousands on the development of the combustion process/ power and metal desighn concept. So having worked in the industry for five decades, I would say without doubt follow the individual car manual reccomendations fo your fuel requirements.

In general you will find using lower grade fuel in you engine will result in other costs such as unburnt carbon on the valves which in turns negates an eventual top overhaul,loss of power etc. So you are not saving anything in the long run.

As for gasahol versus benzine, There are different opions regarding it's benfit other than cost, since 95 became unavailable it has cost me a few thousand baht in engine repairs.

That's my twopenneth for what it is worth,

Cheers

[dave_boo]

FWIW, in my CBR 150 I noticed a 25% drop in consumption (40 down to 32 km/L) when going from benzine 95 to gasahol 91...

I can understand your interest in making comparisons perhaps to satisfy your curiosity. However to make a point.

When engine manufacturers design and built and engine, they literally spent thousands on the development of the combustion process/ power and metal desighn concept. So having worked in the industry for five decades, I would say without doubt follow the individual car manual reccomendations fo your fuel requirements.

In general you will find using lower grade fuel in you engine will result in other costs such as unburnt carbon on the valves which in turns negates an eventual top overhaul,loss of power etc. So you are not saving anything in the long run.

As for gasahol versus benzine, There are different opions regarding it's benfit other than cost, since 95 became unavailable it has cost me a few thousand baht in engine repairs.

That's my twopenneth for what it is worth,

Cheers

Also of concern is the fact that Honda doesn't certify this bike for use of gasahol. I don't know if the milage would be better if the jets were changed to compensate (I'd assume so and the fact that others are using fuel injection probably explains the smaller delta between the two). I'll defer to your experience, and the only reason I posted is to provide what appears to be a worst case scenario.

I do have a question though-does the ethanol in the gasahol prevent the carbon build up that is claimed from going to a lower grade?

[somluck]

Most Japanese cars can take lower octane fuel but most European makes need higher octane or 'knocking' will occur and can damage your engine

[PeaceBlondie]

Dave, the earlier CBR150 was only listed for 91 benzene, although I wasted money buying a few tanks of 95 benzene which made no difference. I cannot imagine how you saw a 25% decrease in fuel efficiency in your switch. My 2008 model runs the same on all four grades, and we both have a compression ratio of 11:1.

The general advice from experts has always been that the extra octane ratings are a waste of money if the engine does not ping/detonate on a lower octane level.

[dave_boo]

Dave, the earlier CBR150 was only listed for 91 benzene, although I wasted money buying a few tanks of 95 benzene which made no difference. I cannot imagine how you saw a 25% decrease in fuel efficiency in your switch. My 2008 model runs the same on all four grades, and we both have a compression ratio of 11:1.

The general advice from experts has always been that the extra octane ratings are a waste of money if the engine does not ping/detonate on a lower octane level.

I'm just reporting it like I saw it....and if anything, the gasahol was the most ideal situation since by the time I knew where I was it was straight shot home on nice inter-city roads at around 110, whereas the benzine usage was tearing up and getting lost in the mountains at any speed between 40 and 110....

[keemapoot]

I'm concerned that in addition to phasing out regular gasoline (benzene) 95; that 91 will also be phased out. This is a concern for me because I have some older special collector cars that required 95, but which I now run on 91, unsatisfactorily.

This is a quote from the Shell head office representative on this issue the other day in issues/answers section of the Phuket Gazette, when asked by a reader why regular is no longer available at Shell. (although I did notice some from comments in the thaivisa Phuket subforum saying they found 95 non gasohol recently at Shell). However, this comment is from the supplier itself, so presumably is reliable.

"We have stopped selling gasoline in accordance with government laws. As a result, we have had to change to simply supplying gasohol. We tried our best to phase it out as gradually as possible so people's needs wouldn't be overly disrupted. Soon, if they wish to comply with Thai law, no gas stations will sell gasoline, only gasohol."

Friday, March 20, 2009

emphasis added

If you believe this quote, soon, no gasoline at all will be available in Thailand, forcing all older cars either off the road or to be modified.

[harrry]

Tests for milage and performance without reuning the vehicle would be useles and in fact give completely opposite results to the possible.

[hulahula85]

Most Japanese cars can take lower octane fuel but most European makes need higher octane or 'knocking' will occur and can damage your engine

Not after 1984 or 2527 All modern cars come with knock sensors that will automatically retard ignition timing to avoid predetonation or "knocking". It's only meant as a safety feature, it doesn't mean that someone can always run lower octane fuel and just live with the reduced engine power.

Just better to use the manufacturer recommended rating, you're not going to get more power from higher octane unless the ignition timing is electronically tuned and advanced, and/or the car has a turbo or supercharged engine and boost is increased. Higher octane with no tuning usually means less power because it takes more time for the air/fuel mixture to be completely burnt.

[dominique355]

Octane is a measurement for the "unwillingness" of a fuel to burn; the higher the octane the more unwilling to burn.

High output engines usually have a high compression, thus risking a premature explosion. These engines need high octane gasoline. Most modern and efficient engines have high compression or are supercharged and ask for at least 95 or even 98 octane.

For reasons I don't understand Thailand seems to favor low efficient engines which use 91 octane. IMO that's a waste of energy.

Now, simply using a higher than recommended octane gasoline will not increase the efficiency, i.e. power or mileage of a car. Only if the engine is so sophisticated that its ECU can adapt fuel and spark timing, maybe 95 instead of 91 yields some improvement. But I don't think such engines are commonly sold here.

The risk that an incomplete burning leaves residues in the combustion chamber and on the valves is much more likely.

It's a pity that all these modern and highly efficient new European engines are not imported into Thailand. We only get the "3rd world"-versions built here. Once again the government's tax and excise policy favors the polluting technology.

[johnefallis]

Most Japanese cars can take lower octane fuel but most European makes need higher octane or 'knocking' will occur and can damage your engine

Not after 1984 or 2527 All modern cars come with knock sensors that will automatically retard ignition timing to avoid predetonation or "knocking". It's only meant as a safety feature, it doesn't mean that someone can always run lower octane fuel and just live with the reduced engine power.

Just better to use the manufacturer recommended rating, you're not going to get more power from higher octane unless the ignition timing is electronically tuned and advanced, and/or the car has a turbo or supercharged engine and boost is increased. Higher octane with no tuning usually means less power because it takes more time for the air/fuel mixture to be completely burnt.

Right, and wrong. Actually the knock sensor allows the computer controls to advance the timing just to the point below which it will ping, or predetonate. The main purpose is emissions, although this affects many things. This means that any engine under heavy load, like driving uphill fully loaded, would be more likely to ping from the load, so the engine retards the timing so it won't ping, retarding the timing reduces the power output. Hence the higher octane fuel, which does burn longer, allows the timing to stay further advanced, therefore providing more power. Any vehicle which is emissions legal will function this way, it keeps emission such as HC and CO at their minimum levels.

Whether the rest of the car is designed to benefit much from this, is doubful. High performance cars with high HP ratings are designed and programmed with an advance curve to provide maximum power on demand, hence they recommend the higher octane, but it is not necessary for typical driving. PERIOD. The computer will simply retard the timing just below the point of predetonation anyway. Use of different types of recommended fuel is also meant to maximize what normal refining produce, but that's another story.

The main problem with using gasohol is NOT performance, as it burns cleaner and has the SAME octane rating as it's gasoline counterpart, it is because it is more corrosive to the the fuel delivery systems not designed for it. The rubber, the steel, the aluminum, etc. Newer cars, especially Toyota, have addressed this in the U.S. and though more expensive, they are fitting fuel systems to be able to handle several different types of fuel now.

With this all in mind, you can see how making everyone use gasohol will get the old cars off the road, the fuel will simply destroy the car over time and it will be too expensive or not possible to repair. Bye bye old car, hello new car.... oh, and hello new car taxes.

Of course, they are doing it for the "environment". W.T.F.-ever!

In closing, using the fuel recommended by the manufacturer is best, with few exceptions, unless you simply can't get it anymore.

John

[johnefallis]

Now, simply using a higher than recommended octane gasoline will not increase the efficiency, i.e. power or mileage of a car. Only if the engine is so sophisticated that its ECU can adapt fuel and spark timing, maybe 95 instead of 91 yields some improvement. But I don't think such engines are commonly sold here.

.....

ALL of the cars sold here have that ability, it is the primary function of emission controls (to adjust the fuel delivery-ie. Dwell or pulsewidth-and the ignition timing). This has been the case since the early 70's. Prior to that the advance curve, or spark timing as you call it, and fuel delivery, was adjusted only for maximum power output on a given curve.

I'll try to answer your other points in a following post.

[dotcom]

As for gasahol versus benzine, There are different opions regarding it's benfit other than cost, since 95 became unavailable it has cost me a few thousand baht in engine repairs.

95 became unavailable where?

[dotcom]

Yes I was also considering the cost difference. When the prices were high, there was a much greater difference in the cost per km. Now the margin is much smaller. I haven't calculated it recently, but I would say I save about 4-5000 baht a year using 91 gasohol (based on 25000 kms a year). So yes its more economical to use 91 gas, but only marginally so in my case.

You are still using fuzzy math. You got much better mileage using normal gasoline (petrol). So how is gasohol cheaper?

[johnefallis]

Octane is a measurement for the "unwillingness" of a fuel to burn; the higher the octane the more unwilling to burn.

High output engines usually have a high compression, thus risking a premature explosion. These engines need high octane gasoline. Most modern and efficient engines have high compression or are supercharged and ask for at least 95 or even 98 octane.

For reasons I don't understand Thailand seems to favor low efficient engines which use 91 octane. IMO that's a waste of energy.

It's a pity that all these modern and highly efficient new European engines are not imported into Thailand. We only get the "3rd world"-versions built here. Once again the government's tax and excise policy favors the polluting technology.

These issues you are perplexed about can most easily be answered with an analogy.

Imagine, if you will, a cow. When you milk it you get a bucket full of what? Milk? Butter? Cream? Chocolate shakes? No. You get many different things mixed together, but through the "refining" process you can get several different things in varying amounts from each gallon. Each with a little different consistency. Each in a varying quantity from each gallon. Left to seperate, the fatty thickest cream can be taken seperately, and so on. Then you can make a certain amount of different things like butter, ice cream, whole milk, non-fat milk, 2% milk, whip cream, cheese, etc., from the different components of what came out of the cow.

If everybody just wanted thick delicious whip cream (high octane) then you could only make a small amount from each gallon as it requires the 'cream' and also require additional "refinement" (the whipping). So do you just throw the rest away? No, you make other things. And you market those other things in a different manner as well. Make different things, appeal to different tastes, sell at different costs.

Crude oil is in many ways similar. With varying amounts of refinement and cost, you get things like diesel fuel oil, lubricants (oil, grease), varying octanes of gasoline, plastics, etc. from each barrel of oil. They try to use as much of what comes in every barrel, minimizing waste. Ever wonder why things don't just run on crude? It is after all the hydrocarbon the rest of it is based on.

Manufacturers generally make cars to run on the fuels available.

As far as Thailand is concerned, although there are other factors, they limit what you can buy here based almost entirely on efficiency and tax the living sh!t out of anything else. That's why almost every auto is 4 cyclinders or below 3 liters, and motorbikes are mostly below 250cc. with the bulk of them below 150cc. All of which require certain emission controls. I think the new Honda CZi motorbike is almost fully adapted to the new world standards.

Hopefully now you better understand the reasons. I've never tried that analogy before, but it seems it should work better than the technical mumbo jumbo that would come out otherwise, and that many would have difficulty understanding. Let me know if my message got through.

John

[dotcom]

Octane is a measurement for the "unwillingness" of a fuel to burn; the higher the octane the more unwilling to burn.

High output engines usually have a high compression, thus risking a premature explosion. These engines need high octane gasoline. Most modern and efficient engines have high compression or are supercharged and ask for at least 95 or even 98 octane.

For reasons I don't understand Thailand seems to favor low efficient engines which use 91 octane. IMO that's a waste of energy.

Now, simply using a higher than recommended octane gasoline will not increase the efficiency, i.e. power or mileage of a car. Only if the engine is so sophisticated that its ECU can adapt fuel and spark timing, maybe 95 instead of 91 yields some improvement. But I don't think such engines are commonly sold here.

The risk that an incomplete burning leaves residues in the combustion chamber and on the valves is much more likely.

It's a pity that all these modern and highly efficient new European engines are not imported into Thailand. We only get the "3rd world"-versions built here. Once again the government's tax and excise policy favors the polluting technology.

I am not going to dispute any of the above. I disagree with it. BUT

Let's examine from a different point of view.

Imagine you have 2 containers, each containing one liter of fuel. One is 91 octane - the other 95 octane - each at 65 degrees F (this is very important).

The 95 contains more "energy" - as measured by BTU (British Thermal units) kilojoules ; or what ever standard you like.

So Dave Boo's result is exactly what I would expect.

My motorcycle, just like his - uses a carburettor. We have no O2 sensors, knock sensors, the timing & the air fuel mixtures are fixed. They will travel further on a liter of 95 than they will on 91. FACT. The internals will also be cleaner.

[culicine]

Yes I was also considering the cost difference. When the prices were high, there was a much greater difference in the cost per km. Now the margin is much smaller. I haven't calculated it recently, but I would say I save about 4-5000 baht a year using 91 gasohol (based on 25000 kms a year). So yes its more economical to use 91 gas, but only marginally so in my case.

You are still using fuzzy math. You got much better mileage using normal gasoline (petrol). So how is gasohol cheaper?

I got better mileage using regular 91. However, gasohol, at that time, was much cheaper. So much cheaper that it was more economical to run on gasohol (cost per km travelled is calculated for both fuel types and compared). It's not that difficult to calculate. Do you nedd the formulae and an example?