Its already paid for itself.

 

That is a very clean ride! 260lb-ft at the flywheel right?

Actually, as far as performance I was agreeing with you:

"What I am getting at is, though I would be more interested in what the OE calibrators have to say, random guy at the dealership or random honda tech may be right when he says you would see little to no gain for using better quality fuels, but only because the computer cannot recognize or perform what it hasn't been programmed for.

So if the most aggressive tune they dyno'd in was for 91, that's the best performance you'll see. Though on 93 the car may run cleaner, smoother and more consistently as a fouled, stale or watered down batch of 93 still has a better proportion of octane to less stable heptane."

But, in saying that, if the tables allow for MBT timing on a better fuel, the difference could be tangible. So maybe instead of OE safety margins we see 18* timing on top instead of 16* or 17*

If the effect is similar on timing around peak torque (VE max) for the L15A there could be gains/loss of as much as 10hp at the flywheel.

When I used the word "cleaner" I should have said there are usually more detergents in 93, though in addition to this, a more full combustion from better timing advance, and a longer period for the flame front to expand there will be less waste sent out the tailpipe thus making the emissions cleaner in the sense that there would be less partial or unburned charge. Plus if you have a Cat installed thats not like >2.5" your emissions are going to be squeaky clean, even at idle on any pump gas option.

Have you tried 91/93 in your fit? I have, it felt a little more lively in the midrange, but I have no data to back that up at the moment. Do you have an AT or MT Fit? That could make a difference as the extra torque will be absorbed by the fluid converter since we cannot currently lock line pressure or install manual valve bodies in Fit ATs, at least from what I can tell.

EDIT: Since Texas Coyote was kind enough to share his findings with a Scan Gauge, which I am guessing is some sort of OBD2 logger? A couple others have chimed in to this effect as well. It now appears that there could be evidence to the theory. So perhaps the Honda engineers decided for folks who get 98 RON or better in canada and europe, that a few more cells could be added to the table.

For now I can only speculate based on my experiences with other platforms and look forward to clarifications

I would also like to point out that I never said the car would learn, I was discussing that the car may simply not have tables to deal with anything better than X octane or worse than Y octane. As far as being reserved for forced induction only, I know there are more than a few but the best that comes to mind at the moment is Hyundai's 4.6L Tau V8 and it's response to changes in fuel grade are appreciable, I think on the order of 9 or 10lb-ft. Which doesn't sound like much but in a 4 valve cylinder head like ours at 10.4 compression VE is sustained for a long time, so 9-10lbs across the whole rev range is huge.

Because horsepower is derived from torque, you will get more HP in return after VE max or above 5252rpm where the curves collide in the equation..

Think of how much money people on this forum will spend on an intake pipe, headers, throttle body and exhaust to maybe achieve +15 or 20hp, when they could've just spent a couple bucks on better gas to reach the same result..

Just my 2psi

 

Though you know the naysayers will just say your ass is not calibrated correctly and you are just perceiving to feel something. The ScanGuage doesn't lie, it's not like it is giving false information and it and the ECU are working in cohoots to fool you into believing the ECU is compensating for a higher octane fuel. No wait, that is exactly what the pair are doing.

 

This engine is 10.4 compression ratio. In any other car, you would automatically think, "That's a high compression ratio." Why should it be any different, just because this one is a Honda?

Secondly, this same engine is sold in Canada, Europe, and Japan, where 91 octane is sometimes the LOWEST you can get.

Ask yourself: why would Honda spend the extra money to tune 20 different ECU's to run only on the typical fuel of every individual country where the Fit/Jazz is sold, when they could just use a table of all possible fuels, and sell basically the same ECU worldwide?

 

Actually there are some here who feel that is not a high compression street motor, though they fail to remember or know that the highest CR B16 that reached the US was a 10.2:1 and never did get the 10.4:1 or 10.8:1 B16A or B16B JDM motors and yet it required/recommended premium fuel. Don't even want to get into that though, because I am pretty sure I know what will be said.

 

The knock sensor is constantly hitting the timing point at which ping occurs, drops a few degrees and gradually returns to the point of pre detonation ping detonation regardless of fuel octane rating so you are safe at no lower than 87 octane but it is igniting at a position much closer to TDC to avoid damaging detonation in the combustion chamber..... If you happen to buy some fuel that is old or contaminated the octane may not have th advertised octane and if it is lower than 87 you are going to have problems.... There are sales brochures that state that the required fuel is regular but the owners manual states that 87 octane is the lowest octane rated fuel you can use in the Fit.... The ECU optimizes performance by advancing the ignition timing to perform at its best on higher octane fuel.... There are threads where this is explained by Honda of America and professional tuners that were written here on fit freak years ago because of this misunderstanding about the technological abilities to adapt to lower octane fuel but it is going to result in a loss of power and fuel mileage.

 

Exactly right, many post 1989 ECUs operate this way.

 

My old 79 Lincoln Town Car with the 2v 400M engine even worked the same way yet people argue all of the time that the Fit is not sophisticated enough to have the ability to adjust to different octane ratings..... Our 95 and 97 GMC 4.3 liter V6s pull back on timing when the engines over heat or have bad fuel in them. Thew old Bosch lamda systems of the 80s and 90s adjusted timing to maximize higher octane stuff and pulled back the advance to save the engines from burning valves or melting pistons on numerous European cars and motorcycles in the 80s and 90s.

 

Yep, those ECMs are a mystery to many, but it doesnt seem to stop them from making wild guesses and statements.

It's funny you mention the old bosch UEGOs because I still tune with lambda, it's basically an excess oxygen sensor which is really helpful. on any fuel 1.0 is stoich. I do have the controllers read out in gasoline scale AFR sometimes though, just because more people are familiar. even though explaining the gradient from .7-1.0 lambda is pretty straight forward.

Unfortunately stock ECUs can only do so much when you take them beyond the airflow they were designed for, and as I mentioned in another thread this can lead to pizza slice shaped pieces of exhaust valve hats magically vaporizing.

I accidentally spike to 21psi on a tune only meant for 15psi on an old project engine and managed to get off the gas quick enough where I saved my turbine and housing and had it dump out to atmosphere.

 

340lb-ft if GMPP is to be believed. No it hasn't been dyno'ed (before or after the tune). It's been mussed up some since that pic was taken. Before the tune at this altitude max boost was around 17lbs, after about 22lbs, although GMPP claims up to 30 at sea-level.

No way. The most optimistic gain "from better gas" would be few percent, within the margin of error so the realistic gain is zero. I think there are wider differences between two batches of the same octane and brand of gas. Certainly not 15-20hp on any car designed for regular fuel.

 

A few percent on a 109 peak HP engine is a few horsepower, more than enough to feel in a 2500 pound car.

 

because honda specifies regular fuel.

different rating systems (at least in Europe and Japan). They use RON. We use (RON+MON)/2, the average of RON and another rating that results in a lower numeric value than RON alone. 91RON is pretty close to 87 using the (RON+MON)/2 method. sheesh.

Ask yourself what is the difference between different octane ratings. The answer is not energy content. HP/Torque and MPG are unaffected by octane rating assuming the car is designed for regular fuel. Economy cars (the Fit is in this category) are designed this way; they can eke out as many joules on regular as premium without knocking.

Now once you hang a blower on the intake (turbo, super, leaf) this is no longer true. But that's not what the argument is about.

 

sigh... it could be a few percent less. The Car and Driver piece I linked a few posts back had this result on an Acura when they ran premium fuel.

 

I got caught up in the reg/prem fuel thing. Three tanks of each averaged showed me no appreciable difference. I'm not going to obsess over the issue, it's too much like herding cats. FIT runs and performs just fine on regular fuel.

 

Half-truth. Honda specifies AT LEAST 87 AKI fuel. Meaning "anything less will cause damage." Nowhere is it said that the L15A runs best on that fuel.

Octane rating - Wikipedia, the free encyclopedia

Looking at that list, one can see several major markets where the Fit was sold for several years before it was ever brought to North America, which countries have 95 RON as the lowest available fuel. Notably, in Hong Kong, only 98 and 99 are available. In other countries, like Russia, fuel as low as 80 RON is available.

Why would Honda go to the trouble to make 10 or 15 different ECU's specifically tuned to the fuel in ONE country, when they could sell the same one worldwide, with built-in adjustment?

I still don't get why you keep harping on energy density. Not one soul on this thread has asserted or even implied there's any more energy in one grade of fuel than in another. Could it be you yourself don't understand what's being discussed?

The argument is about whether the ECU has the capability to dynamically adjust timing for different fuels. Texas Coyote and myself have OBD2 loggers which indicate clearly that it can and does. SilverBullet has a Hondata link:
Knock control tables
that explains exactly how Honda's knock control works. What evidence do you have to the contrary?

I rephrase my question: in any other car, a 10.4:1 compression ratio is associated with "performs best with premium fuel." Have the good folks at Honda somehow managed to repeal the laws of physics?

 

340lb-ft is plenty of twist in a little rear wheel drive car.

22psi at altitude huh, so the turbo is already working harder for less, but yet they are quoting you an +80lb-ft bump at the flywheel on only 5psi more? If it will truly allow you to see 30psi at sea level I would be wary of coming down from up there in case you don't have enough injector or the fuel pump can't keep flow up at 30psi over base fuel pressure, which is pretty common even for aftermarket pumps.

Are you on a stock regulator and return line as well?

What turbo are you running? What compression is the engine? Peak timing and AFRs??

Granted, I and others around here @ ~600ft above sea level are running 30-36 psi on pump 93 only, but that comes at the sacrifice of spark advance and on lower static compression usually <9.0:1CRs. Not to mention really rich tunes, 10.8-11.3:1AFRs at WOT for most of us. This is with only 11-14* peak timing across the setups I have had a hand in.

Yes I said 36psi on pump gas, that gentleman in particular is using a 62mm BorgWarner which is still sitting in the 72-76% compressor efficiency islands. My 59mm BorgWarner is also efficient in this range, but for insurance I run methanol injection.

I would avoid such absolute statements personally. There are a lot of factors you are neglecting here. Especially since none of us have the actual Fuel and Timing tables in front of us. How do you know what the most optimistic gain is without any numbers in front of you? How did you calculate the margin of error?

No where did I suggest that there was a discrepancy in energy density between regular and premium. But what you aren't addressing is the fact that if the ECU allows for it, which it seemingly can according to those providing actual data from scan tools, there is no reason why the tune couldn't allow for >10hp gains from a change of fuel.

With target AFRs a couple points leaner, and an added degree or two of timing, 15-20hp is not at all unreasonable, even on such a small displacement. Another thing to consider is with better fuel, the power gain is across the board, not just at peak output. That includes mid range and bottom end.

+5hp or +7lb-ft from idle on up can really feel different in a car this light.

The Tau V8 example I used is on a very mild tune in a luxury sedan. It is also only one data point, like the Car & Driver Acura example you cited.

There are several things that affect power output. Ambient temperature and pressure, operating temperature as well as fuel quality are just a few. So even back to back test with the same car will produce different results even with control variables from morning to afternoon to evening.

They are also not Honda Fits, which is what we are discussing.

Also, your example of 91 RON, is (perhaps intentionally) neglecting the other fuels, like 98 RON (which in many cases is equivalent to 94-95oct) or greater which is common in several places outside the US.

Additionally in an earlier post I touched on the subject spectrum of quality across similar octane fuels. Especially because of the wide variety of blends throughout the year and their various states of decay/contamination I would still prefer to run a default better fuel to address this.

Perhaps we will have to agree to disagree?

 

Well said, there seems to be lots of speculation, distraction and opinion on this matter taking the space that should be filled with fact in this discussion.

 

It is a fact that the Fit will run well on 87 octane fuel and that the ECU will advance ignition timing to take advantage of higher octane fuel. Some people's cars are driven in a manner that allows them to feel the benefits of an increase in octane and others don't.... No where in my owners manual is it stated that my car is tuned specifically for 87 octane, it is stated clearly not to use fuel with less than 87 octane. That is because the ECU will not adjust to fuel rated lower than 87. I think it is wonderful that the Fit runs well on 87 octane fuel.... If my driving style and environment was similar to that of people that have positive results with 87 octane fuel I probably would have done likewise before I decided to bump up the power with boost..... If the timing was fixed and unable to adjust there would be no reason for an intelligent discussion as to whether there is a difference or not.... That is not the case because a scan gauge substantiates that with premium fuel you are using a lesser percentage of throttle opening and more ignition advance while maintaining a given speed on the same stretch of road under similar weather conditions.

 

ok folks this came from the 2009 fit owners manual in pdf form from honda link page 198.
"Fuel Recommendation Your vehicle is designed to operate on unleaded gasoline with a pump octane number of 87 or higher. Use of a lower octane gasoline can cause a persistent, heavy metallic rapping noise that can lead to engine damage. We recommend using quality gasolines containing detergent additives that help prevent fuel system and engine deposits. In addition, in order to maintain good performance, fuel economy, and emissions control, we strongly recommend, in areas where it is available, the use of gasoline that does NOT contain manganese-based fuel additives such as MMT.
Use of gasoline with these additives may adversely affect performance, and cause the malfunction indicator lamp on your instrument panel to come on. If this happens, contact your authorized dealer for service." 87 or higher

i think this should be self explanatory

so i am going to preface this again by saying that i am not an engineer, however; the folks from honda are, they wrote the manual and established a bottom threshold for fuel tolerance. your car will run on 87 but better with higher grade fuel, so steve244 be cool, you don't need to test the competence of the forum's members. use what ever grade you want.

 

I drive the Fit a lot as many here do, year round it sees roadtrips, camping/hunting trips visits to family in all corners of the country, it's even been to canada

With that said I have had to put a whole lot of different types of gas in her, and I am not always nice to the car, so when it is down on power I notice.

For almost three years now I have had the '08 Fit Sport 5spd and simultaneously a '96 Accent(Cam/Timing/Intake/Header/Exhaust/35 shot NOS, sold), '92 Laser (S259 turbo), 95' Talon (18G turbo, pending sale), an '04 RAV4, and finally '97 Ram Turbodiesel (compound turbos HT60 feeding HX40, sold) All cars have been accumulated over the years, and the couple that were sold were all this year plus the one pending to a local friend who got the turbo itch.. in order to fund new projects for 2011.

When you go from vehicles with few hundred to more than 1,000 lb-ft of wheel torque down to almost exactly 100lb-ft several times a week, sometimes several times of day, your butt dyno becomes pretty well calibrated. Do you know what 12sec 1320's feel like in a >7000lb street legal dually pickup truck? It feels like being in an apartment building launched off the deck of an aircraft carrier

The Fit certainly makes the most of its 109hp, 106lb-ft and makes a great base line for performance comparisons. Especially with stock Fit vs. modified in any fashion, because a few percent gain can be tangible.

In this case we are discussing fuel modification.

So what all this is getting at is, when I get 87oct out in the middle of Nevada or Wyoming or Nerbraska I can feel the car is slower and not running as smoothly as it does on the Shell 93 I routinely use on the North Side of Chicago. Not saying Shell 93 is the best by any means but to illustrate the difference between a big name, consistent station with high customer traffic in an area with very expensive high performance cars, plus alot of heavily modified ones, and some guy named Bob's gas station/garage in bumblefuck.

So when I get back to a city with proper 93 which I usually run to clean out the system after using crappy fuel the change is apparent, though not exactly dramatic it helps below 3krpm especially, because lets face it, the Fit is pretty anemic when it is not screaming at the top of it's gutsy little lungs.

Case in point 87 is fine but it is the MINIMUM recommended. There is no reason yet presented with hard data (Car & Driver aren't exactly SAE material) that you couldn't make a tad more from better fuel.