We use premium fuel in all of our vehicles and power equipment both 2 and 4 cycle..... Our GMC Sierra hadn't been cranked up and driven since last summer and the 8 year old battery had to be charged to take it to town for a new inspection sticker....It fired immediately and went to town got the sticker and put $70.00 worth of premium before coming home.... It sounded like the spark may have been a little weak but adding some injector cleanser had it back to normal before I was back to the house..... Premium really does stay usable for over a year and won't gum up carburetors unless they are out in 100 plus heat for a couple of years.... Ethanol in regular fuel will screw up a small engine in a very short period of time.

 

The ECU in the Fit can't adjust the curve for premium gas. The only thing it can do is retard for knock.
Premium fuel has less energy per given amount the regular fuel do to the fact its harder to ignite. Only engines equipped need use premium fuel to make more power. Like a new BMW 5 series.
But an old pile of crap car may knock less with premium fuel. But only because the chambers are full of carbon and crap.
I have played a lot with bikes on a dyno and I have seen firsthand the difference in power by using regular fuel in certain engines.
In a Fit, premium is just a waste of money and economy.

 

You are underestimating the abilities of the ECU the Fit is equipped with..... I have also spent some time with different bikes on a dyno and race tuned a few to run on 108 octane fuel with some very pleasing power and fuel mileage increases.... You are equating the volatility of low octane fuel with energy... Yes the higher the octane the more resistant it is to pre ignition from high compression and carbon and crap raises the compression in the combustion chambers of cars that are neglected or not properly tuned and premium fuel eliminates pre ignition.... The L15A engine has a rather high 10.4:1 compression ratio and Honda has programmed the ECU to where it will run safely and ping free on fuel with an octane rating as low as 87 that they say to use fuel with no less than but at the same time the ECU will adjust air to fuel ratio and ignition timing to optimize performance with higher octane fuel..... If you don't have a free flowing intake and at least a cat back exhaust and don't use but 50% of the power band save your money and use the minimum recommended octane fuel..... If you have spent money for after market intake and exhaust changes to pull more air through the combustion chambers and use 90% of the power band with the throttle down on a frequent basis it is in your best interest to spend the money on higher octane fuel especially if your exhaust changes include more than just a cat back pipe because at that point of flow velocity you will be running with combustion and exhaust temperatures that require premium and maybe even some octane booster and colder plugs to cool things down..... You could buy a stand alone tuning device to adjust the ignition timing back a bit and control the air to fuel ratio instead but using regular under those circumstances will end up costing you big bucks in the long run.

 

The ECU in the Fit can't adjust the curve for premium gas. The only thing it can do is retard for knock.

Yes it can, that is what the oxygen sensor is for. The only problem is that it is not tuned for horsepower but for MBT which is a 13.4-13.8 A/F and with 10 percent ethanol in the ecm leans it out to14.2. Every fuel made as a A/F ratio (A/F that all fuel is burned). C16 would work fine if it didn't destroy the oxygen sensor and CAT., it has a A/F ratio of 14.8 which is higher than 13.8 for regular. 14.4 for Premium Gas. The ecm adjusts for Temperature, Humidity, Barometric Pressure,Octane, Ethanol, and how you drive. Open loop is what is pre programed in the ecm from the manufacture. Closed loop is from the reading of the sensors. At full throttle a car would go into open loop for horsepower at 12-12.5 A/F.

 

:sigh: I give up.

 

Exactly my point.

 

This has been debated to death...........
If you think that premium fuel is going to give you HP and economy go and dump it in.

 

This is a key point. Ethanol degrades substantially over a very short period of time however in Canada even our premium has ethanol blended.

 

That's a dangerous statement to say man unless u actually helped building the Fit But yeah, like people and u said it's up to us if we wanna use 93 or 87. I personally see the difference so I'm going to keep on using the 93 one

 

Premium gas might get 1 mpg better, or 3% better mpg, maybe, because it does have more btu per pound as a result of the components, mostly toluene, that increases octane, but the cost is generall about 8% more so you lose money. The engine compression is generally the most important spec that calls for higher octane (premium gas) but its not the only one.
The Fits we know all use regular gas except at the track with no problem.

 

I have a few questions,

1. Doesn't premium have have a higher gravity weight .735 regular .755 or higher for premium?

2. Doesn't toluene expand when heated, like Diesel? So volume in tank expands?

3. If you fill your tank with 87 w/ 10 percent ethanol and check octane in a quarter tank it will be lower than 87 octane?

4. What the difference between RFG and premium with 10 Percent ethanol gas?
5. I thought regular has more BTUS per pound But Premium has more Btus per gallon because it weights more?

I agree for the most part but I think it more like 10 percent. Thanks SB

 

If it gives a few more hp at a certain rpms but peak hp remains the same do you have a horsepower increase? Ive dynoed my Fit so I know because my sons friend owns a speed shop and has a dyno. They were surprise that the fit produced so much torque and thought hp would be lower. 82 hp and 102 torque at wheels 14.2 on the wide band. Found out later pedal didn't go to floor because of over sized floor mat, so it would be higher.

 

I'm just not interested in using it. Even if I got one or 2 more MPG's out of premium, since I am spending more for it, I still might not be coming out ahead cost wise anyhow.

 

It just on option, there is alot of people with low mileage on there cars getting 10/20 mpg less than me. Gas mileage should peak at 15,000 miles and stay steady until something breaks. City driving is very hard on an engine, the oil stays colder and the upper engine is Hotter then it should be. Fuel will boil in the injector and you will burn more fuel to replace it. Cost of reliability is a small price.

 

it sucks our cars aren't clear like it is on corvettes.. they flat out tell you that you can use 93 octane and the ECU will adjust too it.. OR you can use 87 octane and you can adjust to it.

........where as the honda fit.. it gives you just a minimal you can use.... well duh is there anything less then 87 octane?

does anyone have proof of evidence that the honda fit really takes advantage of 93 octane? or is this just a guess?

my boosted car had 5 tune setups and they were all done under 93 octane.. so it makes sinse i stayed at 93 octane cuz all of my tunes were dyno tuned with it.. but man.. i WISH i could have used 87 octane.

for the honda fit tho.. this is MY Personal thing iam doing.. iam going to run 87 octane untill theres hard evidence that our cars can really use 93 octane like its ment to be used. because what honda tells us doesn't say anything about 93 octane.. it just says don't go under 87 octane... WELL freaken ANY CAR in that case will go by the same rules.. its not going to hurt ANY car if you go too high of an octane because your ECU is designed to throw a specific amount of fuel in anyways according to 87 reguardless.

I mean.. someone check out the Civic SI manual 93 octane or greater... the Honda Fit says 87 octane or greater... i kinda see a pattern here... or maybe iam just the only person here on CRAZY pills and iam the only one using 87 octane with major performance being robbed from me.

 

Good questions, Did I confuse the issue? cheers.

 

Laws of phyisics... you can't create energy from nowhere. Lower octane fuels have more energy per volume than higher octanes (87 octane 250 BTU/gal, 100 octane 200 BTU/gal, 87 octane gasahol 206 BTU/gal). If your engine requires higher octane (higher compression) to create the HP it was designed for... use it. If your car was designed with low octane... use lower octane... it will give you more HP at any operating condition it was designed for. And, it can't give you more just because you added more octane.

If additives are the issue, make the decision based on this.

 

Where'd you get this stuff?
Consult any ChE handbook for the heats of combustion of gasioline: about 115,000 BTU per pound Since a gallon weighs about 6 pounds thats 690,000 BTU per gallon. Having run a few thousand combustion tests I'll vouch for the amount of heat available from gasoline combustion. Generally speaking premium gas of higher octane has a few more thousand BTU per pound than regular because its components have higher heats of combustion.
Octane level is basically needed for higher compression engines due the vapor-air pressure at ignition.
Gasoline is composed of literally hundreds of chemicals, toluene being one, and it is the combination that achieves the necessary octane rating. Few gasolines have the same exact formulation day after day because the crude its derived from isn't that consistent either.
The power from a given engine is entirely at the mercy of the sum of the heats of combustion for the dozens of components. And in most cases premium will have components with higher heats of combustion than lower octane fuels simply because those components have lower octane ratings. often they cost less to make too.

 

I'm with you except for the less energy of premium gas. My running lots of combustion tests on both premium and regular say premium has more BTU per pound. Not much mind you, and not always, but there is a difference, mostly because the components that have hifgher octane ratings, such as toluene, also have higher heats of combustion.
Yes you are correct, racers have long boosted their gas content with adding toluene. Very carefully as toluene can have some nasty side effects if exposure is too much, both engine and personnel.

 

[QUOTE=einstein77;855758] If your engine requires higher octane (higher compression) to create the HP it was designed for... use it. If your car was designed with low octane... use lower octane... it will give you more HP at any operating condition it was designed for.

I agree.... The L15A with a 10.4:1 compression ratio is designed to run on higher octane fuel than the minimum recommended 87 octane that the ECU is capable of adjusting to run on, nothing lower.