i think that many people confuse the terms when it comes to this topic. "low" in the description of low octane fuel does not mean "of a lesser quality"....just as "high" in high octane does not mean better! it only means different. as i stated long ago, the BTU content of a gallon of 87 and a gallon of 93 are both hovering around 120,000 BTUs. there will be no increased power from a stock fit engine by using either of these two fuels. with similar btu's going in, the same power will come out! it's basic physics and we have yet figure out how to cheat it! sorry.

the octane number does not tell us anything about the fuel other than it's ability to withstand pressures and prevent pre-ignition. methane has an octane rating of 120.....so why don't people run out and put methane in their cars? exactly, because it won't work, it's not designed for methane and not only that, methan has way fewer BTU's per gallon so it would suck in a stock fit engine.....

just because some people out there want higher octane and expensive gas to make a difference in something, doesn't mean that it will....and yes, that's my opinion.

 

How do you know? Have you tested this yourself?

It has nothing to do with different energies going into the cylinder. Like you said, it has everything to do with the fuel's ability to resist pre-detonation from compression.

However, if an engine has the technology to advance the timing accordingly, then you get more compression and that does equal more power.

Just like I said in my post above about personal experience with an Infiniti G35. The car achieves its best power on premium fuel, but has the technology to allow it to run safely on lower octane.

And just like someone who posted about their Oddessy achieving its best power on premium fuel...

I'm not saying that's the case with the Fit, but how can you say otherwise without personal experience or knowledge from Honda?

There are a few too many baseless opinions on these forums.

 

a knock sensor does nothing until the car "knocks." it is not and active piece of the engine, it is a reactive piece! meaning, it does not increase timing...increase timing... increase timing ...until knock and then back off for optimum performance, that wouldf be what i mean by active. everything i've read about these things is to the contrary! not only that, when a car knocks, to fix the problem, the car "Retards" this is why your Infinity could run on lower octane....it's a one way street kind of deal. the engine designers have designer an economy car and the knock sensor is there to protect the investment of the consumer. but you could try and hack the system to advance the engine knock sensor if you'd like i wouldn't....i'd turbo charge!

 

yes yes yes....timing from the computer is probably what you're really meaning and about to jump down my throat about....but that does not matter!!!!!....... if your engine does not knock on 87 octane with your foot to the floor in your fit, it most definitely will not knock on 93. this is where all things are equal and you will not be able to yank more power out of the same car, doing the same foot to the floor activity, on 93 octane! it just can't physically happen when the BTU's are the same(relatively) the engine reacts the same to the same input......the gas pedal reacts to the input.....the oxygen sensors react the same to the same input .....the computer reacts the same to the same input........so how do i get more performance out if nothing has changed? answer that and you've elevated yourself to the most sought after engineer in the world soon to make millions!

 

The way you state it, if you got a tank of bad gas with an octane of 85, timing would be retarded, and your car would never advance the timing after that. Of course the knock sensor allows the computer to advance the timing and lean out the mixture until the car knocks, then it retards the spark a bit and richens the mixture a bit. Some fuel injection computers are programmed with a certain limit (eg, the AP1 S2000 cannot take advantage of fuel with an octane rating of better than 91 IIRC)

However, it is only limited by the programming in the fuel injection computer. I cannot say for sure that the Fit doesn't run better on higher octane ratings, but I also cannot say that it does. I have tried regular and I've tried premium and I seem to consistently get better mileage on premium. This may simply be a coincidence, but I can't prove it either way because there are too many variables.

The fact is that I don't know. I know how the system works however, which seems to put me in the minority.

I'm sure somebody is going to suggest that since the S2k doesn't do it, there's no way the Fit does. Perhaps you're right. But the Fit with its OBD II computer is 7 years more advanced than the original S2k so it might. I don't know. Most likely you don't either.

 

I'm not TRYING to be a jerk here, but once again, you're talking about something you don't know about. Leaner mixtures produce more power. They are also more prone to knocking and create more pollution.

Stoichiometric air fuel ratio is 14.7 parts of air to 1 part of fuel. No common street car gets that lean (Honda Hybrids do it occasionally and beyond, going as lean as 23-1)

The closer you can get to stoichiometric, the more power you can get out of a given amount of fuel, so yes. You can get more power out a given amount of fuel because no gasoline powered cars that are commonly available today use all the power in the fuel we give them.

That was easy, so who is writing me my cheque for my millions?

 

you are missing the point and comparing apples to oranges. and yes you don't have enough information and neither do i, but my guess is trying to be educated within the world of science and i can deduce what would happen if the test were done. i can make the assumtion that the test would not show any significant appreciable difference. how can i say that? read the above. when you start talking about bad gas, hybrids and whatnot....why don't you just fill half the tank with water and try to test that? we have to start at a point and look at the variables that we can control and move forward. with a little help from physics, thermodynamics and common sense, i can put together enough information to realise that doing the test would be a waste of time. the gains, if any, would be seen across the board......... get it?

take one car, put 87 in it bang on the gas, the computer will advance the timeing to gain performance..........if it does not knock, it will perform in the exact way as if it had 93 octane because they have the same BTU content. it's as simple as that...........

what you're talking about is this...."if the car knocks on 87, then the knock sensor will retard the engine, thereby reducing power." that is a completely different situation from what i just mentioned, this is what you are getting hung up on, and this is my point......we have to start from the same perfectly functioning car. and that gets me to it reacting to two different fuels in the same way.

when "a" stock fit knocks on 87, there is something wrong and wil be retarded into less power and the 93 will then give the same amount of power as a perfectly functioning same fit on 87 octane. understand?

 

^this is true and verified by Hondata. The Honda knock sensor does not advance timing significantly enough to say that it increases performance and fuel economy on a stock ecu. The car is originally tuned from the factory to run on 87octane, they do not tune for the possibility of higher octane for "performance" purposes. Adding 91+ doesnt mean it will automatically advance ignition as the ECU sees fit.

Either the ECU will retard igntion, or advance it back to stock timing.

Garismatic is also correct, in some ways. THere is no absolute way to tell if it helps. so MANY variables exist. Running in 14.7:1 is only efficient for cruising and part-throttle conditions. It does not mean its good for WOT situations, as the reasons Garis explained. In WOT, the ecu no longer runs in the "closed" loop conditions of 14.7.

as for everyone's Fits, stick with 87. If 93 works better, than stick with it. All cars are different and everyone's driving conditions are different. Use to what works for you.

 

I see what you are saying. But you are not correct. Learn about mixture. Fuel mixture. That will show you that you are not seeing the whole picture.

Anyway, I'm off on holidays to somewhere sunny and warm! Maybe will pick this discussion up in 2 weeks!!!

 

yep, i don't have any clue as to what fuel mixture has to do with this little thought experiment.....wouldn't the mixture be the same if we used the same car? how does the car know there is 87 or 93 octane in the tank or in the injectors? is there a sensor i don't know about? if our engine monitors oxygen going in and coming out, what does that have to do with the type of gas in the mix? what am i missing here?

have fun

 

i allways pump 93. old habit beacuse of my old EG

 

Ive never used anything for almost 5k miles but shell 93 exclusively, i think the only thing i can hurt is my wallet, but if you think about it even u use 87 u only save less than $2 each fill up... I also keep in mind that the fit engine was designed for use around the world where octane higher... the octane requirment of a car is also influenced by marketing.... think about it, even if the fit requires 93 would Honda dare to put it as a requirment? All cars or "econoboxes" in the class use 87, if Honda advertises for 93 then theyre in trouble

 

Someone with a ScanGauge II or other means of reading ignition timing could test whether the Fit retards the ignition timing when running on 87 octane versus higher octane-rated fuel, and report the results here. If there's no difference in engine timing under otherwise similar driving conditions, that would prove that the Fit's engine doesn't extract any more energy out of fuel with octane ratings higher than 87.

 

Setting all the technical stuff aside, my fit runs a lot better with a higher octane fuel. There is a significant increase acceleration and could reach a higher top speed. This is based on my experience.

 

Look at it this way. The fit has a 10.4/1 compression ratio. The RSX-S has an 11/1 ratio and it uses high octane. Higher compression burns fuel faster. I used to put 93 in my 04 accord sedan with a 9.7/1 compression ratio and I got way better gas milage with it. Also the car felt much faster in top speed and acceleration. Lately I've been using 89 in my fit and I get better gas milage with it than 87. I think I will start putting in the 93 and see how that does. I have about 6k on my car now. I beleive it will perform better on the 93 octane. I will try it and let you guys know if there is any difference. My fit is an auto sport and I use the paddle shifters all of the time. We'll see how it goes.

 

Then chances are good you will feel that it does, even if it doesn't. Informal tests like this are particularly prone to confirmation bias, which can be avoided by making it a single blind test: have someone else fill up the tank without telling you what octane they put in, and then you decide which it is based on performance. The more times you can repeat this test, the more reliable your results will be.

 

Hey fellas,

Just something to throw out you guys regarding this topic. I noticed no one mentioned Sulphur content in a given octane rating. 87 octane gas (for the most part) usually contains more sulphur than 91 octane. Read some gasoline data and you'll see this. Now, I have yet to figure out what damage sulphur can do to your engine, other than perhaps leaving deposits in the chamber which would lead to a drop in performance over a period of time. I do know that sulphur does damage your cat converter.

Now, I always use 91 shell for my Fit (with the exception of one time because of a fuel shortage in Toronto), and while at the pump one day I noticed a sign. The sign reads that 87 contains 15% Ethanol, 89 contains 10% Ethanol, and 91 contains 0% Ethanol. Perhaps someone can confirm, but I can't remember what the Honda Owner's Manual says about Ethanol. I do know to stay away from MMT, but that's about it.

Anyway, what I'm trying to say is, is that there's a lot more to the octane rating than just numbers. I too also believed like many of you that higher octane is nothing but a waste of money. But as I read further and further into it, I found that 87 octane is formulated differently than 91, not just for its combustive properties, but also its overall quality.

I guess another way to look at it, is using between Synthetic motor oil or non-Synthetic motor oil. Both do the same job, but one goes the extra mile to provide better protection.

 

10.4/1 is high compression. Higher compression requires higher octane fuel. This is so there is no premature detonation. 87 gas burns quicker than 93 or higher. It does say in the manual 87 or higher. If Honda only wanted you to run 87 in the fit it wouldn't say or higher. Plus their not going to say it runs better on 93 because it would hurt their sales. People don't buy econo cars to fill them up with high octane fuel. So honda tunned it to run on 87. But, I'm sure the car will adapt perfectly to higher octane fuel. You would probly notice a difference after a couple fill ups of the higher octane fuel. I am going to put some 93 in on my next fill up. I'll see if its better for fuel economy and a little more power.

 

That is an interesting difference, since ethanol is sometimes added to increase octane rating, and also because ethanol contains about 34% less energy by volume than gasoline (MTBE contains 19% less, for comparison). A reasonable question is, what is Shell adding to raise the octane rating?

It's important to keep in mind that in this case, the higher octane (and lower ethanol) gasoline might contain more energy, but it wouldn't be inherent to it being higher octane, but rather to a higher energy additive being used in place of ethanol.

 

Higher compression requires higher octane fuel, or a later spark, to prevent detonation. Hence how higher compression engines can automatically cope with lower octane fuel by retarding ignition.

It says "87 or higher" because 87 is the minimum that Honda recommends running in the engine, because that's the fuel that was used for their performance ratings. It should be able to run on lower octane fuel, with the knock sensor detecting any knocking and retarding ignition as necessary, with decreased power output. The question is, can it advance the ignition when running on octanes higher than 87? That's the key. Without that, there would be no increase in power.

There's no question whether the engine will adapt to higher octane fuel, and there's no reason that it should take several tankfulls to notice a difference, if there is one. (Except for that confirmation bias that I mentioned earlier.)