Was running 87 octane and was averaging 36 mpg since I got the car. Winter blend gas came into the pic and my mileage dropped down to 33 mpg. I switched to midgrade 89 octane and my mileage went up to 37 mpg. Switched back to 87 octane and mileage went down to 33 mpg again. So I am back running 89 octane and my mileage is back up to 37 mpg. Not broken in yet, about 4500 miles on the clock. Oh, am running the most available gas in the area. It isn't Shell or BP cause you can't buy that around here. It comes out of United Refining in Warren Pa. 90% of the gas in this area is supplied by them and they have the various additives injected for delivery to the Big Boy stations, along with their own additive package. Think I will be running midgrade 89 until summer blend comes out again, and then we will do some more experimenting again. Put the wife's Focus on 89 too, and its mpg went up too! Lousy ethanol and winter blend combination in my opinion.

Edit: Filled up this afternoon with 93 octane for the heck of it. Mpg is bouncing between 39 and 40 mpg. My mpg was down to 34 mpg this morning due to steady rain. Noticed it drops when it is raining for unknown reasons. Once had a old Mercury Marquis with a 429 ci engine in it. It did not like regular and would ping when I ran it. I started blending regular and premium 50/50. I got the blend down to 1 gallon of premium and the balance regular and she would run great.

 

Just so every one is aware the Honda fit/jazz calls for 87 putting in a higher octane does nothing helpful. I know some one has most likely already stated this fact but all your doing is paying more. I drive like an old man on a sunday and get around 36-38 MPG (you can convert that to Liters because I am not going to) Its more about how you drive than anything

 

This is what ignorance looks like^

Please, share your layman's Car & Driver/QwikTrip "science" with us. I need a good laugh.

As a warning.. I have direct access to ECU data, fuel/timing tables and sensor outputs.

 

Well, all I can say is: "There is a principle which is a bar against all information, which is proof against all arguements and which cannot fail to keep a man in everlasting ignorance--That principle is contempt prior to investigation".

And it is a fact that I can not currently get anywhere near 38 mpg when using 87 octane gasoline, but I can get all of it plus more when using 93 octane gasoline. And it is also a fact that I have been in more than one refinery laboratory and do know a bit about the topic.

 

Have put 2000 miles on my Fit since purchase last month. Always use 87 octane, Shell when possible.
Car now has 6400 miles. Highest MGP was Ocala to Bradenton, FL, 46.1 MPG, speed 60, A/C off, cruise on.

 

Yes I have no idea what I am talking about you are right. You are so smart.(said high heavy sarcasm) There is countless data showing that if a manufacturer calls for 87 that putting in a higher tess does nothing unless you are running forced induction or have a high output motor. I am glad you have access to "data" please post your data so I can be proven wrong. I know you will not as it will show nothing. I have been working on cars since I could hold a tool and yes if you put 93 in a big block running 10:1 you will see better power and MPG. In our cars it makes no difference other than that you don't want to look stupid for spending more when you go to the pump.

 

Pop quiz!

What compression ratio does the L15A1 and A7 run?

Now I want to see what mental gymnastics you have to do to backpedal and parse away from that statement in order to tell me how "generic Chevy big block" is different than the L15. Whether its an old W series 348 or an RPO 427.

I work on domestics too by the way. So this could be fun to watch.

My data is all over this forum. Go find it. There are screen shots and everything. I'm not going to waste time on you. We have an adaptive ECU, it will advance timing and adjust fueling to nearly anything you put in it.

87 being the MINIMUM allowed by Honda before damage can occur. It is by no means designed solely for 87. I can see knock on 93 under certain conditions, you should see the knock-sensitivity levels on a hot day with 87.

This is 5* knock retard in action on 93oct E10 under low load/low throttle in 3rd @ 45mph, a common scenario in a Fit:


2 counts of knock registered on cyl #1. And thats with nice cool 57* inlet temps. Them's the facts Jack.

You can dislike what I'm telling you, or how I am telling it.. but that doesn't make it incorrect.

 

I like how you say you will not "waste your time" as you took plenty of time writing this and posting. The bigblock 10:1 was referring to a high output motor. Not specifically the compression ratio. My fit has 83000 miles an not one single issue all run on 87 and getting an average of 34 mpg over the course of those miles.

 

Yes because typing something up, making a phone call, then hopping on my photobucket to grab a screenshot is super time consuming. I just wasn't going to give you a full dissertation and logs of data.

High Out Put huh? Lets look at specific output ratings then.

78HP/Liter SAE Net is very much high output compared the SAE Gross ratings of 61HP/Liter on a Z11 BBC.

You weren't getting 34mpg on that 427CID either. Let alone if it had emissions equipment

 

Looking at the reported mpg in this thread we can also look at the debate in terms of what is the cost per mile and how many miles can you get from a tankful based on the octane you purchase.

In my calculations, gas cost per mile is roughly $0.10 regardless of the octane. I ran the numbers based on previous examples of 87 octane = 33 mpg @ $3.43/gal, 89 octane = 37 mpg @ $3.65/gal, 93 octane = 39 mpg @ $3.85/gal. The big assumption here is that higher octane actually results in higher mpg, but for purposes of discussion, let's assume this is true.

So what does this mean to me? I can go 63 miles further between fill ups by purchasing the higher octane. Looking at both ends of the spectrum, With 87 octane I'll get 350 miles to a tank for $36.36 = $0.104/mile, and with 93 octane I'll get 413 miles per tank for $40.81 = $0.099/mile. Based on these numbers, it costs roughly 10 cents per mile driven, regardless of the octane purchased, however the advantage would be with 93 octane you could go 63 miles further per tankful and not cost you any more than if you had filled up with 87, and got 350 miles per tank.

I think I just talked myself into switching to 93 octane!

 

I'm sorry but IMHO this car does not really need anything other then 87oct
unless you just want to spend the extra money for peace of mind.

I have 17K on my 2012 Fit and I average 30mpg no matter what octane in mostly city driving.

I had a 2011 Mustang 5.0 with a blower and I had to run 91 and I would occasionally run 100oct or add Torco at the track.

I also had 87oct tune that I could load with my hand held tuner if I could not find 91 or higher when traveling.

The Mustang also had adaptive ECU that allowed the Coyote to run 87 you would just be down on hp a little compared to 91.

There was no way I was going to keep using 91 when I got my Fit if it was not required.

I occasionally fill with 91 but usually stick with 87 or 89 it all depends on my wallet at the time I need gas

 

As long as you are acknowledging that the ECU can adjust, that is all the understanding I am looking for.

There is no premium gas stazi going around and forcing anyone to use it.

 

Thanks DSM for the continued interest in keeping the threads sane and free from inaccurate info.

My question to you will not require you to spend an inordinate amount of time answering it I promise.

Now that I know that the ECU will cause the engine to always adjust to the fuel grade supplied to it can the same be said about CAI, aftermarket exhausts, heck anything else we attach to these little engines? And what about plugs or better oil or whatever else we can imagine to improve performance?

And finally did honda make the ECU so that it will adjust for fuel economy first and then performance or is it a middle of the road kinda thing?

And if the answers to my questions are as I suspect does salvation lie in a company who will produce a gizmo that either bypasses or replaces or modifies what Honda has preprogrammed? And can they actually make one that is plug and play and doesn't require a PHD in car stuff to install?

And if the engine advance or retards to prevent knocking then is there that much room for improvement in the engine? Enough to make it worth ones wild to even buy a way to modify the ECU? And......if the engine is modified to always run at the top end of its potential what are the dangers of that?

 

[QUOTE=DiamondStarMonsters;1158610]Yes because typing something up, making a phone call, then hopping on my photobucket to grab a screenshot is super time consuming. I just wasn't going to give you a full dissertation and logs of data.

High Out Put huh? Lets look at specific output ratings then.

78HP/Liter SAE Net is very much high output compared the SAE Gross ratings of 61HP/Liter on a Z11 BBC.

You weren't getting 34mpg on that 427CID either. Let alone if it had emissions equipment[/QUOTE

So by what your saying as it has a learning ecu that putting in 94 as compared to 87 does not make a difference. thank you.
Also I was mostly stating that driving habits effect MPG more than what fuel grade you use..if you are going to say that is not the case then you are just refusing to be wrong

 

[QUOTE=thatfitguy;1158670]I suppose if my aunt had balls then she'd be my uncle, yes. Selective understanding is an incredible thing.

I do agree that a large part of it is up to operator habits, and the only person refusing to be wrong is you. You have a "faith" in a belief on this matter, several of us have an actual understanding with corroborating data.

 

Thanks for posting this bro, i was messing around for fun and decided to put in 91 for fun last week (its only like $1 more on a tank) and about maybe 30 miles later i felt like it has slightly better throttle response off the line (this is before putting on my light weight wheels) but thought it was all in my head because i put in 91. I go through gas alot so i dont make it a habit but every now and again i will throw in 91 if there isnt much price difference. Usually i pop in 89 or 91 in the summer months on my other cars because its hot and the AC would probably bake the engine where the 87 will barely suffice. My 03 4runner used to ping under hard acceleration in the summer heat so i put in 89 in the summer and 87 in the winter.

 

The ECU is most pre-occupied with simply sticking to the target lambda its programmed for in closed loop/sensor feedback operation. It has the ability to run at stoich and in closed loop under a surprising amount of conditions. You can be on certain parts of the tables under WOT and the ECU will still be targeting lambda 1.0 (14.13:1 AFR on E10 gasoline)

Which in this case is for fuel economy purposes, which I would argue is a facet for performance. A high-performance motor is by definition efficient. For its size, it certainly impresses. Even dressed down with luxuries of A/C and emissions concerns.

So anything you can do that helps fight pre-ignition for example would go to improve both fuel economy and torque production. Because Spark Advance angle is directly related to torque through the rate and angles through which cylinder pressure rises, peaks and subsides. As well as the heat energy we are able to release efficiently from the charge. Running at stoich will enable you to get the most heat for the smallest fuel mass invested. But if you can't burn it at the best angle for leverage on the crank you are wasting energy.

At a certain point load dictates that you need to add fuel and start to run richer, which is different for every single motor, even of identical configuration.. you have to start feeding in more fuel in proportion to air to control the burn and still run an acceptable amount of spark timing. The fuel cools the combustion chamber and the air-charge through the phase change from liquid to gas, evaporation.

So there is a relatively fine balance in all of this. And by tuning fuel, spark timing, spark plug heat range or "temperature" and gap, hitting the sweet spot for IATs, etc all play a part.

This for instance is what a very mildly modified spark table looks like for the L15A1 found in the GD3 Fits:


Now compare that to this almost stock timing table:

As you might guess, the one on top provides a cleaner pull and it was matched to work with the users specific VE modifications to be used on 91oct fuel in a car that sees a lot of short-burst WOT events for extended sessions on an Auto-X circuit.

(Note to future FlashPro users who find this in a search: This is unique to that car and driver's uses, and is likely not a match or best fit for your car, its mods and the environment you run it in.)

Timing advance attack and nominal advance figures are usually increasing in a curvilinear fashion with engine speed. The Fits engine, using a form of VTEC has a sudden change in airflow/VE in the mid-range, which is where that hump comes in, and then it dives again around peak torque leading up to and after 4800rpm.

These are points where the motor is prone to knocking/detonation. You can see this in my cruise log above, a little bit of throttle on a cool day accerating across a flat road in 3rd in the upper 3k revs and some spark timing is pulled because the knock sensor picks up suspect frequencies.. confirming 2 counts of knock. This was using 93oct E10 fuel. It's more dramatic on 87. So by losing 5* of advance, you are changing when and where in the rod/crank angles cylinder pressure is maturing and then fading.

Cylinder pressure is directly related to torque, and horsepower is derived as a function of torque over time. Anywhere you have more cylinder pressure/torque you have more power.

The fact that timing is being actively retarded is telling you the engine is persistently trying to create a certain threshold of power, but physical inconveniences of atmosphere and fuel are prohibiting it. As far as running a tuning device, my hope is that Hondata will come out with a FlashPro for the GEs.

It's a massive leap forward over piggybacks, and incorporates many of the flexibilities of a full standalone, without some of the drawbacks for your average consumer. From multiple perspectives it would be worth while. Diagnostics/Codes, performance or economy. Being able to tune for your relevant VE mods is huge. Even a small percentage gain is noticeable in a car with less than 100whp from the factory. Especially one this lightweight.

 

As best I can understand your post^^^^

I had to rewrite my post since I did some research to understand what you wrote.

 

Just because Rampo brought it up:

Cost per mile is a great way to look at it. I ran the numbers comparing my personal mileage with 93 and 87, and taking into account the price difference where I live, which is $0.30 per gallon. The cost per mile for me was almost identical with both, because I would get slightly better mileage with 93. The difference was less than $1 over a whole tank's worth of driving.

So why do one over the other?

93 usually has higher quality chemicals and more engine-cleaning additives.
93 may give you more fun factor (if you're into that sort of thing).
93 should allow you to fill up less often (unless you just really like standing around at a gas pump).
If you're anti-ethanol, 93 usually has less of it, so you can stick it to the corn people if that's your thing. (I like burning ethanol, but that's another subject).

It's up to you, but don't knock it till you tried it 3 times (see what I did there?).

 

It's funny about this octane thing if to use 87 or 91. If you go to some European forums they say 87 is crap, the lowest octane they have is 95, 91 for USA. Benefits if using 91 ? More power ? Higher MPG ? In both cases yes but little difference but the biggest difference is that 91 octane is much cleaner than 87, USA talks about being green this green that so why we have 87 as the lowest octane ?