I've always been under the impression that if a car is really and truly optimized to run on 87 (rather than just CAPABLE of running on 87), running on 89 or 93 won't return any meaningfully increased performance.

The octane the car is optimized to run on is a function of the timing. If you change the timing, then you can run on (and benefit from) higher octane levels of gasoline.

The question then, is the car really optimized for 87, or is it just able to run on it (and runs better on higher octanes). It's entirely possible that the timing has been altered from other markets for USDM, I guess someone can play around with that when they get their Fit. It'd make an interesting write-up, trying different timing settings, fuel octanes, and then making dyno runs. Someone with a shop maybe?

 

Dyno time must be almost free in the US. When it costs several hundred dollars here you don't do it unless you need to for track cars or very major mods (turbos, chargers, etc). A tank of fuel to find out is a lot less than a dyno run.

We work on the principal - If it brings a smile to your dial then its worthwhile. Don't need a computer to tell me a basic difference you can feel with any bumometer.

The car is not optimised for crap fuel it can just run it if it has to. ie. just capable of running it. You don't need to mess with timings the car will adjust given decent juice. Thats why it has sensors and computers and stuff. It not an old carby.

 

I believe the manual is worded that way primarily to proclaim slightly higher octane levels as acceptable. For example, California offers 91 octane but other states offer 92 octane instead.

For best overall results, stick to the lowest octane level available that is still greater than or equal to the manual's recommendation.

 

Extra performance? Not likely.

As for fuel economy, I have seen just the opposite. A relative used to have a 99 TL. That engine would advance or retard the timing as appropriate, and when filled with 87 instead of 91, it got nearly 5 more miles per gallon. Of course it accelerated like a slug.

 

I've been running my Fit on the recommended 87 octane gas for four tanks now. Just recently, I switched over to 89 octane gas. I noticed a BIG difference in performance. I bet MPG will increase too. Even though the owner's manual only recommended 87 octane, that was referring to a stock Fit. Mine has a cold air intake on it right now, so I think I would need 89. I will never go back to 87 again! However, I believe that jumping up to 91 octane is overdoing it for me.

 

No, you didn't notice an increase in performance. Further, 5bhp from a cold air intake is not nearly enough to justify needing to jump to a higher octane fuel. Don't kid yourself.

The only time I'd EVER put higher than 87 octane in a Fit is if it was turbocharged or supercharged.

Why? Higher octane fuel holds less potential energy/btu's.

That's why high performance cars need high octane fuel: It burns slower, decreasing chances for detonation.

The Fit has a 1.5L 109hp engine. Anything more than minimum grade 87 octane fuel in the Fit is a complete and utter waste of money. It was formulated for 87, so run it. You guys running higher octane acting like this is a performance engine are fooling yourselves. Spend good money on synthetic oil and good transmissions fluid, as these will decrease friction and increase economy/performance to a point, but don't waste it on higher octane fuels.

Just use a good name-brand 87 octane and you'll never have a problem. It's those no-name brands that suck.

FYI, previous (yet old old old) posts in this thread are somewhat misleading. Sure, Japan has something like 98RON fuel. Problem is, we don't use RON as our octane rating. Ours is RON+MON/2. Their 98 is the equivalent of our 93. Their low octane is the equivalent of our 87. They don't get special gas there that we don't get here.

Hell. There's a gas station near my house that sells 100 octane unleaded, and 116 leaded from a pump. Bet they don't have pumps like that in Japan! (I used to fill up my turbo 350z with the 100 unleaded from time to time. I know that after a few miles, the ignition timing would adjust a little bit and I'd get a few hp I think. I did it more for peace of mind though when running during hot weather at the track than anything else......for detonation prevention.

 

Does a CAI really add 5 BHP to the Fit? Is that verified by dyno? Just curious. I know 5 BHP is not much, but on a 109HP engine, it should be noticeable, right?

 

109bhp in the fit is something like what, 80whp? so 5bhp, minus 20% drivetrain loss, maybe 3whp.

I can pretty much guarantee even the most finely-tuned butts cannot seriously feel 3whp.

I call this the "placebo effect". The intake is louder. The loudness must=power, right? So your brain tricks you into thinking it's more powerful, and that you feel a significant difference.

With higher octane, no, you're not making any more power. It's all in your head. Even if you were to make 1-2bhp more, you'd NEVER be able to feel it and tell the difference. Hell, 1-2hp is well within the range of error in a dyno.

 

Look. This is my point in all this. The Fit is a great car. But, in my business we use the term "it is what it is".

And the Fit isn't a sports car. It's not even a sport-inspired compact. It's a subcompact car with peppy handling and the lowest hp of any car Honda sells in the U.S. It's an econo-hatch.

So don't get carried away with it. Don't waste the money on high octane fuels. Don't be tricked into thinking the 5-10bhp your intake/header/exhaust gave you makes you more than .2 second faster in the 1/4 mile, (from what, 18.5 seconds to 18.3 or something). It is what it is.

And I think there are better ways to apprecaite what the Fit is and what it can do than street driving. Take it autocrossing! Properly set up, a Fit could dominate an autocross course. On 87 octane and 80whp

 

87 is recommended. No need to go any higher.

 

That's about what I figured. I believe Honda engineers are already getting about all the good that can be gotten out of this engine. Short of turbocharging, et cetera, that is.
Thanks for the information. I'm sure this has been talked to death in other sections of Fitfreak, but since I don't race or mod for performance, I just don't really go to those sections.

 

When I stepped on the accelerator with 87 octane I noticed a slight delay in acceleration. With 89 octane, I did not feel that delay at all. I will continue to refill with 89 octane gas regardless of price. A little more costly is not an issue.

P.S. I was using 87 octane Chevron gas right before I switched over to 89 octane Chevron.

 

any delay in throttle response is not due to the fuel you used. It's due to the DBW programming and the learned response by the ECU to your driving styles.

Changing driving styles from day to day can alter the response of the motor via the ECU learning procedure.

If you want to continue wasting your money, feel free. Just know that you're driving an econo sub-compact with a 109bhp economy motor that has no hint of sport, speed, or acceleration in it.

 

I already know that the Fit is only a sub-compact, thank you very much. I'm not trying to make into anything sports-like. I was just posting my own experience with gas octane changes and did not expect any outright rebuttal; it's not like I'm running premium.

 

Hey, Trant. Thanks for that info.
I'm about to try pouring 91 into my tank for a while. With my daily driving, I have achieved a fairly consistent 44.5mpg on 87 octane (that's over the past, oh, 8,000 miles). The computer should be able to advance the spark farther with the higher octane, thus producing more power per expansion stroke for a given amount of gasoline.
Experimental data in my previous car, a Saturn L300, showed that switching from 87 to 91 octane yielded a 10% increase in mpg (from 21-22 up to 24) for about a 6% increase in price at the time. It will be interesting to see if I get similar results in the Fit; both cars have a 10:1 compression ration. I'll run about 5 tanks before I draw any conclusions, so don't expect me to report back in less than a month.
I'm sure some people are so sure of what they know that they'll tell me I'm wasting my time, whether or not they've bothered to experiment themselves. Whatever-- it's my money, not theirs, and I'm willing to spend it to learn something.

--Barry

 

Higher octane would cause the ecu to retard timing, not advance. Different grades of octane show MINIMAL differences in BTU's so no you are not going to make more power; definitely not anything you will notice. But hey believe what you want to, you're not wasting your time, just your money.

 

FYI:
Higher Octane Gas - The Myth : Gas Saver Guide

Even better info on what octane means:
MYTH BUSTING: High Octane fuel will make a car faster ? Car Reviews, News & Advice ? carsales.com.au - carsales.com.au

High Octane Gas Myth on Blueprint for Financial Prosperity

Octane - Wikiautos

So, 91 giving better "performance" is all in your head. "placebo effect"

Not to beat the dead horse, but, after reading this, are you SURE you're feeling better performance? Or are you realizing now that it's in your head?

Oh, believe me. I'd be the first to run high octane in all my cars if I knew it made power or better efficiency. Fact is, I only run it in my s2000 and my harley (both recommended by manufacturer to run high test.)

 

Well, that didn't take long.

It's not about BTUs in the gasoline. I understand that lower octane gas has higher heat content than higher octane gas. Advancing the spark allows the engine to create a greater amount of downward force on the piston earlier in the power stroke. It makes more efficient use of the gas, so less fuel/air mixture is needed to create a given amount of power, hence you would see an increase in mileage.
Every engine I've owned says you are mistaken. Do you have documentation to back that up?

To repeat myself, experimental data taken over several tanks proved a 10% mpg increase in my Saturn by using a higher octane gas. I'm not claiming I will get the same results in my Fit, but I might. The only way to know for sure is to try it, and nobody seems to have done that yet in a verifiable way.

--Barry

 

Barry, everything you're saying you did is contradictory to the information I have posted. Sure, I may not be positive about the comment about it decreasing vs. increasing timing, but the potential energy in higher octane fuel is lower than that in low octane, hence the slower burn for detonation prevention.

Higher octane fuel has not been proven by science to increase fuel mileage and power just by using it in any old car.

If the Fit absolutely needed 89 or better, they'd recommend it in the manual.

 

I read the links you posted before I replied the last time. I don't think it is entirely contradictory. The point made in those articles is that "not every" car can take advantage of increased octane, but that's very different from "no car" can take advantage of it. If your engine is a low compression engine (8.5:1 or below), there would be no advantage to it. However, the engine in our Fits have 10:1 compression, which is on the high end for a stock motor. Most small block Chevy's, for example, are 9 or 9.5:1.

If the Fit had static advance like my old Buick Skylark (350 cu. in, 10.25:1 compression), we would have to retard the hell out of the timing to keep it from knocking on 87. I used to run 93 in my Buick; anything less than 91, and it knocked like crazy. I even had a water injection setup for a while-- 20 gallons of gas and a gallon of water, shot straight into the Quadrajet primaries. But our Fits have dynamic advance and knock sensors, so the timing can adjust depending on the driving conditions and fuel octane.

I think the reason they recommend 87 in the manual is that it is adequate for most driving conditions, since the car can adjust for it, and recommending a higher octane rating would be a barrier to purchase for many people.

Anyway, it's time for me to make my experiment. I will shut up for a month or so, until I've run 4-5 tanks of 91 through my Fit, and then I'll let you know if it made a difference or not.

--Barry