The mpg depends on how much energy is produced when the fuel-air mixure burns. Most, but not all the time, more energy producing compounds like toluene are in greater concentrations in premium fuels but not always. Ethanol has much lower combustion energy so it really isn't a benefit. MPG drops when its used..
Ethanol can be an octane booster but the combustion energy of ethanol is much lower than typical gasoline; worse, it costs more energy to produce ethanol than gasoline and wouldn't be used at all if it weren't for government subsidies. So the use of ethanol is limited.
As for retarded timing, that doesn't happen in FI systems with computer control. When slowing the fuel injectors are cut off so no fuel reaches the combustion chamber til you get close to idle speed. Til then the firing. So when you slow down do it in gear, not with engine idling. And in any case the spark advance matches the rpm curve regardless whether the engine has fuel-air mixture in the comnbustion chamber.
And little if any gas gets washed into the oil sump unless your rings are really bad or the fuel flow is very poorly regulated.

Again, its virtually always uneconomical to use higher grade gas than necessary. An energy booster, like most injector cleaners, will help but again not economical. Its use is strictly keeping passages clean.

 

Regular grade fuel only meets the minimum octane requirements that are needed for a Fit not to ping..... No where in the owners manual is it recommended to use 87 octane fuel, it just meets the minimum requirements only .... It has been proven that the ECU will adjust to to benefit from higher octane fuel.....My fuel mileage figures convinced me and it isn't costing me more than $1.00 per tank to use premium and, there is still an increase in performance and no need for additives to clean the injectors and possible carbon accumulations in the combustion chambers from the lesser amount of ignition advance.

 

Might be important to note that premium ignites slower/burns slower. That is why it gets rid of knock and ping and that is why you can advance timing, run boost safer etc. Though I am not a chemist specializing in fuel, I have done some product testing for Yamaha snowmobiles. Engineers for the 4 cylinder 4 stroke 1000cc 150 HP engine say to run 87 because premium will cause more carbon build up and not be any faster. And this I have verified at radar runs.
As far as the fit goes, I think it boils down to how aggressive the fuel/timing maps are, and how they correct to a knock sensor.
I suspect that you wont get less carbon build up with premium.

 

Take it from this old refinery engineer: there isn't enough difference in the energy content of premium vs regular to pay for a 5% difference in price. And the difference in additives isn't that much either. And the difference in octane ratings now vs way back when is simply because carburators simply weren't precise enough to meter gasoline at the precision that prevents to pre-ignition.
You can run premium gasoline but unless you're on track at speed its a waste or unless you climb steep hills. Otherwise there won't be a preignition problem and no retardation will happen.

 

That's my understanding as well, assuming you're talking about gas from the same company. There is a benefit to paying more for 87 octane from a reputable company because it will have more additives than the cheap 87.
I was wondering about that too. The spark advance readings in that other post were all taken at WOT (wide open throttle). If you drive that way a lot, for example a lot of city jumps from light to light, or if you live in Reno and work in Tahoe, then premium might work better for you. But at milder throttle openings and light load I suspect it would just be money out the exhaust pipe.

 

It is all in your mind that you're getting better gas mileage because if you started using 87 from the start, you will be getting the same gas mileage you are getting now. You're just giving the oil companies extra profit for a car that doesn't require premium gas. The difference is about 3+ dollars every fill and that is a lot of money every year for people that fills their tank often. Higher octane gas was made for cars with higher compression to avoid engine knocking.

 

Well put. Very accurately stated. Thanks.

 

I guess that the higher octane works for me for the reasons that wdb spoke of.... Everything is far away from where I live, it is hilly, and in Texas Cities you really have to hustle to stay with the flow or dodge bullets from enraged drivers carrying high capacity big bore concealed firearms..... Seriously...... Things are different here I guess, but other than a 13 month period sent in Vietnam, it is all I have ever known.

 

i worked in Port Arthur; hills? Mt Neiderland elevation 9 feet above sea level; Only hills in TX are in west TX LOL.

 

I guess that about all of Texas is west of you..... Technically I am in East Texas, but really only east of central.... Plainview is 50 miles south of Lubbock and 80 miles east of Clovis New Mexico... It is flat there and the roads are straight It is a a wonderful place to drive a mid fifties Cadillac, WOT for hours at a time or it overheats or runs out of oil or fuel. Which ever happens first and my money is on the fuel.

 

Port Arthur is as east TX as it gets; and yes I drove my late 50's Caddy to Houston for dinner, taking about an hour. (check that on your map).
Mount Niederland, being the highest point around unless my memory has failed again had an elevation of 9 feet, meaning there are no hills in east TX.
I did have a neighbor who , going to Austin, had to get a policeman to park her car. The road wasn't flat enough for her to cope..
And one more:
Neighbor family vacationed to the Smokies on my recomendation; came back mid week. Couldn't handle those crooked roads. Just flat wore them out in 2 days.

Both are true stories

 

I live in San Antonio and we have ridiculous hills here just as well.
Then again, I live in the Terrell Hills and Alamo Heights parts of it - not the downtown areas.

Just because the entire city isn't built on a mountain, doesn't mean there aren't a substantial amount of hills.

 

I went to San An many times and yes they do have inclines; however, for those of us raised in the Smokies or Rockies, they aren't hills.
San An is one of the few good cities to live in according to my friends there and my visits agree.

 

I think we've been spammed! Unless Acai or Goji run well in Fit.

 

going off topic with a lack of Texas talk

formerly thinking higher than 87 octane would be of very little or no value
(yeah sometimes you have to eat crap and admit you could be wrong)

I am pretty sure I am getting about +2 MPG with 93 octane, seem to get better with acetone and 87 vs straight 87 as well.
Not a 100% sure, but it looks that way.........

Somebody else should try it and see if I am FOS or not.

Now back to our previously scheduled program, "An Armadillo smashed my fog light"

 

Interesting discussion on octane ratings here

Personally I've been using simply the minimum recommended octane (93 RON here). My thinking was I'd just pay what's needed to give it the gas it'll run on, and that higher octane isn't really worth it unless I drove some sort of high-compression or turbo monster.

Ran the same octane on trackdays and I didn't have any issues...although maybe I should try the higher octane from time to time.

 

When you spend 8 to 10% more for your gasoline to gain 5 or 6% in mpg thats pretty negative to me.

 

Around here this weekend regular is $2.49 and premium $2.69 per gallon.
Thats 8% increase in cost. In places its 30c per gallon more, or a 12% penalty. The difference between 32 and 34 mpg is 6%.
When you spend 8% more for gasoline to gain 6% in mpg, that isn't worth the money.
You may notice that premium does have higher heat of combustion than regukar, which is why you get the extra mpg and why premium is needed for on-track activity.
And true premium does burn slower, which is why static timing on premium fueled vehicles are more advanced than regular fuel specifications. But unless those premium fuel specified vehicles (BMW etc) are programmed to advance further unless spark knock is detected no advantage is gained but hp is. . Few cars specifying regular fuel have that programmed simply because the gain in hp isn't important..

 

Agree 100% I know you tend to look at things on a purer cost benefit basis than I do (my sense of adventure is just too hard to resist sometimes, just for the plain old fun of trying it LOL)
Entirely logical perhaps 100% right. But I am whacked into being more open minded about this by trying it myself, coupled with the previously cited at the least somewhat credible timing advance noted with the scan gauge. Maybe the timing maps have more aggressive programming than I previously thought.
Again, agree not cost effective, just seems like a lot of fun for me to jack the MPG and performance even if it is incremental. And I have been wrong about this in previous threads, saying premium is a pure waste when in fact it does seemingly provide some value.

 

haha i use mid grade!