octane
from chemistry we remember oct=8 octo pus etc
hydrocardonis what gas is just hydrogen and carbon
many organic molecules are hydro carbons.

Any way think of a chain of these hydrocarbon molecules it is just straight
if you light one end it quickly burns to the other.

now to slow this down, add side chains along the route from one end to the other. this slows down the burning.

An engine should be run on the lowest octane rating it can be run before it pings, knocks, and has other troubles. An average car engine has a compression ratio of about 7 or 8 or 9 to 1 (8:1) modern cars have sensors to tell if the engine is knocking and then it may reduce the spark advance or some thing else. older engines if your old enought to remember would make all sorts of expensive noises caused by gas problems.
my guess is regular gas will be fine and give good gas mileage. I think it would be OK to do a try with a few tanks of premium to see it wont hurt.

Diesel engines have very high compression ratios-and from an engineering analysis that has a lot to do with their higher effeciency resulting in more mpg If I could buy a diesel Fit or other small car I would
My 1980 diesel rabbit got over 44 mpg-I wish I still had it

 

Y'all waste your money on premium gasoline if you wish, I prefer to waste mine on martinis!

 

I used 87 octane for the first 6 months, and only got about 24mpg, so I decided to try 89. The second tank got me almost 27, but the third was about 23 (same drive)! I put in 93 last week, but smashed my car before I got an mpg reading, though it was looking like it was going to be a very good tank!

Keep in mind that the difference between 87 and 93 is about 20 cents, or $2 per 10-gallon fill-up. If I could go an extra 25 miles, or increase mpg by 2.5, then its like getting that last gallon for $2. If gas were 89 cents, it would be a waste, but when gas is $3, its a good deal!

 

If your engine doesn't know what to do with high octane fuel, it's a waste of money.

It's not about being cheaper. The only reason it costs more is because it is associated with high performance vehicles that run higher compression ratios, turbos, and/or superchargers.

I don't think my Fit engine has ever audibly pinged on regular 87, and I have gotten up to 45 mpg on a whole tank pure freeway drive.

But if 91 makes you happy, it won't hurt to use it (perhaps less engine power). I have a friend or two that are sticklers about using 91 actually. *shrug*

 

If I go 250 miles on a $30 fillup of regular, but 275 miles on a $32 fillup of super, which is better, regardless of what the engine may or may not know or be doing?

 

there's way too many other variables involved in how many mpg one gets on which octane to make any conclusions based on a couple of tests. speed, acceleration, driving style, traffic conditions, road conditions, local or freeway...to name a few. if you believe using higher octane is better for the car then go ahead, and if you don't want to use higher octane then don't worry because everything will be just fine using the recommended fuel.

 

And I went 560 miles on a single tank! (But usually I get about 280-320 miles)

But yah, it's sooo hard to pin down whether the change of gas is really the reason, so many variables like the above poster said. Temp, weather, traffic, right foot, oil life, air density, size of the truck you're drafting behind...

In a controlled test, I would be surprised to see more than a couple percent between any of the fuels, for the Fit.

Premium fuel is heavier, weighin' your car down!! (j/k, it's only minimally heavier, but it is.)

 

I would just stick with 87 Octane. My uncle in HK has a Toyota Arias Estima and it is rated for the lowest octane available in HK. However, he thought he would get better performance and life from his van if he filled on the higher octane fuel. In a years time, the engine developed a knocking sound due to the higher octane fuel. Engines that weren't designed for higher octane fuels should not be filled up with higher octane fuels.

 

The most kilometers I've got out of a tank of gas was with 91 (probably shell vpower or Petro Canada Superclean whatever), I didn't baby it either I was mashing that accelerator all the time. I also noticed it felt a bit different at high rpm.. more pep?

I drive about 110-150km highway and city per day every day all at once (span of 2-4 hours).

It's hard getting accurate readings though, who knows if the different pumps detect "full tank" the same or if one clicks off 5 liters sooner than another.

With 87 I normally get approx 470-500km per tank (depending how low I go when the light comes on), I've used 91 two or three times and it was a consistent easy 500-510km per tank each time.

The other day I filled up on 89 just to see what it gives me... I think one month I'll try 87 only from the same station/pump as often as possible.. then 89 the next month and so on.

 

You may be an extra (best case scenario) 40km, you'll probably end up paying an extra 11 cents a Litre and the average fill up is 35L. So to travel 40km on the premium fuel you are paying $3.85. Now my fuel economy is 7.5L/100km, so I'll use my city numbers as a comparison. So to travel 40km, I'd need an extra 3L of gas. Right now, our gas prices are hovering at about $1/L (freaking jumped $0.10 in the last few days!!!!). So basically I'd pay an extra $3 to travel the same distance as the $3.85 for premium fuel. So, it looks like the threshold value is $1.28/L of gas before it becomes more economical to fill with Premium instead of regular 87 octane. Oh man I'm in a whole engineering calculation mode right now, anyone else have more data with 87, 89, 91 octane for me to do calculations with?!?!?

 

im running on 89 all the time i get gas and gas would last me for like close to 7 days w/o filling up

 

I seriously doubt that fuel with slightly less energy that is less prone to pre-detonation had anything to do with that engine symptom... I would be looking for something in the engine that is making a knocking noise and needs adjusting!

 

Noooo my uncle was pretty sure it was the octane of the fuel that caused the knocking sound. My other uncle also in HK is a mechanic and has a shop at a track in China was the one that came up with the cause of the problem...

Even though it is a small amount of energy you are losing, an engine that isn't designed for that type of loss over an extended period of time will suffer. Same reason as to why you need to keep putting higher octane fuels in premium cars with engines designed for it. Just because it has a higher octane doesn't mean that every engine will benefit from it.

 

Sick, lol for a JDM (errr...Chinese Domestic Market) Van. I wonder if they are still Rear Engine like the old ones.

Oh and 87 for the Fit all the way. 320 Miles is my "Range" on Average for a Heavy-set guy.

Plus at these prices $25 to fill up is a huge testament.

 

I know everyone on here is saying they get better gas mileage with lower octane gas, but is it possible to get better mileage with higher octane gas.

I'm asking because my last tank of gas i filled up 35 litres of 87 octane and got 470km out of it (roughly 13.3km/L), but just recently i put 20 litres of 91 octane cuz the gas station i went to ran out of regular and was selling 91 at regular prices, anyways i've driven about 120km so far and my gas gauge has barely gone down at all.

The other thing i was wondering, since 91 octane reduces detonation that would mean that 91 is thinner than 87 right, so would that also mean that 91 weighs less than 87? I'm wondering cuz when i put 20L of 91 it felt lighter than 20L of 87 (note i usually only put 20L of gas in my car when i get gas)

 

I doubt the weight difference is even measurable... but higher octane fuel is a more complex molecule and therefore theoretically weighs more. Octane is basically an inhibitor, kind of like a resistor to help control detonation.

All kinds of things can affect your MPG, given the right circumstances you could get better MPG with slightly higher octane fuel. Sea level altitude and high temps being the most notable cases. Keep in mind you will see an adjustment in octane on base fuel right at the pump anyway.

 

I looked this up a while ago, but I thought it was like 6.6 vs 6.8 lbs/gallon. So 10 gallons would be a ~2 pound difference. Not worth consideration, it was jesting...

How do some posters come to solid mpg conclusions after one tank (or partial tank)...

 

ok ok, it is measureable... I ment more along the lines of negligible

 

All I would like to say is that Octane only makes a difference if you experience knock. Higher Octanes burn smoother in a more controlled manner than Lower Octanes which in turners makes your car feel smoother, but it does not do anything else, it does not provide more power or more mpg, from the federal trade commission,

"At the Pump: Use the Octane Level You Need

• Your owner’s manual recommends the most effective octane level for your car. For most cars, the recommended gasoline is regular octane. In most cases, using a higher octane gas than the manufacturer recommends offers no benefit. Unless your engine is knocking, buying higher octane gasoline is a waste of money."

The only way Higher Octane can help you is to prevent knock and allow you to utilizer a higher compression, so basically if you are using a super or turbo charger which causes the compression to increase thus needing a Higher Octane. the same idea with numerous forms if knock suppression, such as water injection, nos etc etc. all which allow you to put in more air and fuel without causing your engine to knock and blow up and giving you more power...Thus race fuel, and cranking up the boost

sorry for the rant, i got my fit after coming from my eclipse with an upgraded turbo