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stephanie1975

Why Hi Octane?

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I just got my first smart and read that it needs high octaine, does anyone know why? Do I have to also add anthing else? Which is the best brand of gas for the smart?

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I don't add anything to my gas and I use shell vpower because it's the only fuel close to home that doesn't have ethanol in it

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Use lower octane at your peril. The engine's compression ratio is 10:1 and that's high enough to require 91 octane. You probably could squeak by on 89 octane if you wanted......any name brand fuel at 91 should be fine.

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I only use Shell 91 but anything without ethanol is the best choice. Using 91 octane you will see the best mileage, if you run 87 or 89 the mileage will not be quite as good, negating any "savings". The ethanol blended gasolines have less energy than ethanol free fuels. Running lower octane, the ecu will just feed the car extra fuel to stop any knocking.

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Posted (edited) · Report post

What does it mean that ethanol blended gasolines have less energy? It is better for the environment?Where does one get the little car icons to add our stats?

Edited by stephanie1975

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10% ethanol blend has 33.8 MJ/L, pure gasoline is 34.2 MJ/L. From a few items I have read, many producers are blending more than 10% ethanol.

Potential issues with ethanol fuel.

There are two different site the members track the fuel consumption on Fuelly.com and spiritmonitor.de. Both sites have a link that can be added to your signature.

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Ethanol is what's in wine and beer, most of this stuff as used in fuel comes from corn. This has raised corn prices for the poor folk in Mexico and central America. So it's a "green" element of fuel that is creating social problems in poor countries and making uninformed car drivers feel better about themselves.

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my personal feeling on this is the seals in the electric fuel pump isnt ethanol compatible for lower octane fuel. higher octane in north america have lil or no ethanol in it.

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It it so interesting to know that high ethanol is not actually a good thing...I checked out the link (thanks) and there are a few stations near me that are full gas that I will use. Thanks for the info folks!

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one of the ones i know that don't have ethanol is the Chevron 95octane gas... i alternate between that and the 91 /w some ethanolnot sure about the other brands...

It it so interesting to know that high ethanol is not actually a good thing...I checked out the link (thanks) and there are a few stations near me that are full gas that I will use. Thanks for the info folks!

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one of the ones i know that don't have ethanol is the Chevron 95octane gas... i alternate between that and the 91 /w some ethanolnot sure about the other brands...

did my first fill. It cost less to fill than expected and even with using the high octaine (and I found a station that's ethanol free for the 91) the cost for filling was about the same as my old car, which was really good on gas.

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First of all, to answer your question, I accidentally put 89 in my 09 Passion Coupe. It ran, but it really sputtered and coughed. I could feel a loss of power. As soon as I realized what had happened (Full serve station attendant + language barrier), I added 94, but it took another full fill to get it running smoothly. My question is an extension of this one: I'm driving from Ottawa to Vermont tomorrow. It would save a lot of time and bouncing from one exit to another if someone could tell me what brands of Gasoline come in Hi-Octane. From the above post, I can see that Chevron has a 95 grade. Are there Chevron stations in Vermont? What other stations are a reliable source of H.O fuel. My car will run on 91, but I can practically feel it dying a slow death as it pings and coughs it's way down the highway.

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Use lower octane at your peril. The engine's compression ratio is 10:1 and that's high enough to require 91 octane. You probably could squeak by on 89 octane if you wanted......any name brand fuel at 91 should be fine.

Mike, Toyota Yaris runs 10.5:1 compression ratio and only requires regular 87 octane fuel...this is why I was also a bit surprised by the smart car needing 91 minimum. I suppose it also depends on the valve timing and the actual cycles the engine runs on.Anyway, I remember reading somewhere in the manual that if premium gas is not available, regular gas can be used, but engine speed has to be kept lower than 3000rpm.

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The Toyota has a higher tech engine than the 451, so with better combustion chamber design, lower octane can be used. Use 87 in a 451 and you will regret it!

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Use 87 in a 451 and you will regret it!

Fairly certain no one has proven that to be true in a naturally asperated 451. Turbo versions, very much a different story. Edited by Huronlad

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We have had one testimonial about poor running on 87 here, so that is what I am referring to.

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Are you referring to post 12? There testimonial states that 89 octane had the car sputtering. I have an easier time believing they had a bad tank of fuel.My Father erroneously ran 87 octane fuel in my 451 on our trip into the US last year. With the exception of higher fuel consumption, you would never have known it was not running on premium fuel. That was over 3000km. No knocking, no sputtering.

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Top tier gas is what you want to be running in your Smart for best mileage, performance, and longevity of parts. Top tier gas is what is recommended when you buy a supercar... if it's good enough for them, it's good enough for your Smart!

For me, I have tried all the Canadian ones and my Smart runs the best on Chevron. I alternate between 91 and the occasional 94.

http://www.toptiergas.com/retailers.html

Also, as an aside, I wonder if the Smart gas recommendation for Canada/USA accurately reflects the conversion in measuring octane vs. the European way of measuring octane. Example: 87 USA/Canada (RON+MON)/2 = ~91 Octane in European measurement...

Edited by cubeist

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The octane required is mainly just tuning. The manufacturer can pretty much tune the engine for whatever octane they want, unless it is really high compression. They probably could have tuned it for 87 octane, but they obviously decided that tuning for 91 would have some benefits. The price per tank is really minimal. 20L at a 5 cent/L difference is only a buck difference.I have an aftermarket programmer on my truck, and I have a choice between an 87 octane tune or a 91 octane tune. With the 91 tune, I get about 40 extra hp and much better mileage. Actually saves me money on fuel, and that is with 150L, $200 fill ups. I will only put Shell91 in the tank. But that is also because it does not contain ethanol, which is bad to use if the vehicle sits for extended periods. I usually only fill up every other month or so.

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my personal feeling on this is the seals in the electric fuel pump isnt ethanol compatible for lower octane fuel. higher octane in north america have lil or no ethanol in it.

I think you are confusing Methanol with Ethanol. Methanol will eat away at rubber parts, ethanol won't, but modern engines use neoprene in the fuel system components.Have a look here http://autorepair.about.com/library/faqs/bl412i.htm?rd=1.

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The compression ratio is only part of the answer. There are many cars that operate at higher compression ratios, but yet don't require Hi Octane fuelFor example the Mazda 3 engine has a compression ratio of 13:1 using regular fuel.But the Smart car is a low cost design, so it users older engine technology, hence the need for HI Octane fuel in a 10:1 compression engineYou can use lower octane fuel, but he cars computer will compensate, by changing engine parameters, and greatly reducing power and MPG.Blending in Ethanol is a cheap and dirty way to increase octane. But don't confuse hi octane fuel with better fuel. Ethanol has much lower energy content that even regular gas, in spite of the higher octane number.I can't imagine how poor the performance of this engine would be when running on 87 octane fuel with 10% ethanol.I imagine you would see 10MPG lower, and a great reduction in drive-ability and acceleration.The chief benefit to the Smart car, is the low initial cost. If you don't drive it a lot, then it will be a bargain.For the price of a new Smart car , you could buy a 5-10 year old Prius, but let me tell yo, once the Prius is out of warranty, the maintenance costs are extremely high.It's a Myth that the Prius is reliable. I owned one, and it was not all that reliable, and the average MPG was only 40, and that's for a car that costs 2x to 3x the Smart car.The smart car is a simple low cost design, so even when things fail with age, it won't be expensive to fix.

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Good first post, welcome!

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Posted (edited) · Report post

I have had two smarts.  My first, a 2008 passion, I bought used and owned for 60,000 miles.  My current one, a 2016 passion, I have only had for eight months.

The 2008 rather seriously wanted 91 octane fuel or it would get sluggish.  On 89 octane it just accelerated slowly.  Octanes above 91 ran fine but did not increase performance or economy.  My 2016 has the turbocharged 0.9 liter engine and a manual five-speed transmission.  I used 93 octane for the first 1,000 miles and it ran okay but economy was only about 34 mpg (it was breaking in).  For the next 1,000 miles I blended down to 91 octane and it ran just about the same.  Then I tried taking it down to 89 octane.  The turbocharger "kick" was noticeably reduced; but it was easier to drive!  On the higher octanes the car tended to surge forward about a second after shifting and moving ahead; on 89 octane it was smoother.  Finally, I ran a 1300-mile three-day trip in early winter on the Interstate and intentionally used 89 octane the entire time, at speeds touching 80 mph at times and frequently at 65-70.  The car ran great and got 44 mpg the entire trip.  Then, I got a speeding ticket!  I decided 89 octane would save me money (about 30 cents per gallon compared to premium) and was plenty fast for me.  That's all I've used ever since.  I've tried several different brands; there's very little difference from one to another.  

Edited by Wadhamite
A typo!

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For those who wish to run a non-ethanol gas ..... check out this link to find the locations anywhere in Canada or the US.

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Posted (edited) · Report post

On 7/1/2012 at 9:12 AM, stephanie1975 said:

It it so interesting to know that high ethanol is not actually a good thing...I checked out the link (thanks) and there are a few stations near me that are full gas that I will use. Thanks for the info folks!

I wouldn't worry so much about it. I've ran it for years and never had an issue with the stuff... At most you'll suffer a 1-3% loss in fuel economy. It is only really an issue in marine applications or when the fuel is stored for long periods of time because it absorbs water and the fuel rots...That being said, I also ran it on my boat so long as I knew I'd burn through it that weekend. Ethanol has a higher octane rating so it's often blended into gasoline to increase the octane number. Higher octane number does not mean more power. Simply stated it is resistance to knock.

 

Your smart requires it because it runs high compression and highly advanced valve timing (some of them are turbo charged). They've done this to squeeze as much power as permitable out of a tiny engine to make it driveable. Modern engines will de-tune themselves when knock--complicated subject to explain--is detected( from useage of lower octane) to protect its self but the result is an enriched fuel mixture, lower power, and worse fuel economy. However, it is reactive so it(knock) is damaging your engine before it starts to back off timing and richen the mixture up. So yes you can run 87 if you really wanted to but it will cost you in mileage and engine durability. Run what the manual tells you to, in any car... IE: If a car says run 87, don't put 91 in it. Likewise, your car tells you to run 91, run it. 

 

Of course it's much safer to run 91 in a car that requires 87 than running 87 in a car that requires 91. 

 

If you want to know what knock sounds like, it kind of sounds like keys dangling around in your engine compartment or the sound of rain on a tin roof. It's can range from very loud to non audible depending on severity. 

 

Common joke among my friends who have spent years building expensive high horsepower engines is

Knock knock

who's there?

A new engine. 

Edited by kelaog

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