unfortunately, i don't think I have the patience to do a gas mileage evaluation. I've been a part of many many parts comparisons though and there is quite a bit involved in getting consistent dyno runs, even back to back because the engine's temperature goes from cold to efficient to overly hot in the blink of an eye. At the very least I can provide the average AFR's and timing adjustments over the rpm range for a period of time of driving, which could give us at least a vague idea if the ecu is efficiently pulling timing or if it is more worthwhile to stick with regular gas.

Selden, can I quote you for my college professors that give me a hard time for using wiki as a source, even if it is quoted? They may not believe me when I say it is reputable but if I provide them with information from someone with your credentials maybe they will be more lenient.

 

This is why it's so hard to get good data -- it's a lot of work.

Feel free to quote me, but don't expect a friendly ear. And keep in mind my qualification: in certain fields Wikipedia is a reliable source; in others, it's worse than useless. A couple of years ago, I read an article about Jimmy Wales and Wikipedia in the New Yorker, and I well remember a quote that Wikipedia is "infested with moonbats." Ironically, Wikipedia has an article on moonbats. The New Yorker article is worth your time:

Annals of Information: Know It All : The New Yorker

Finally, as an ironic postscript to the New Yorker article, see: Essjay controversy - Wikipedia, the free encyclopedia .

We seem to have drifted a bit from regular vs premium gasoline.

 

back on topic:

in MOST cars that do not adjust timing according to fuel type used premium is bad if it is not called for as the slower burn causes an incomplete combustion cycle and deposits on your plugs, valves, combustion chamber/piston head, and clogs your cat faster.

It is TBD if the fit's ECU can compensate enough timing to make the change from regular to premium worthwhile as far as power goes...I plan to do some research with my datalogger and wideband (when i find them, put them in storage after i sold my tiburon) to analyze rpm vs ignition advance and AFR.

 

Try adding 1 oz. of acetone to 10 gallons of 87 octane..........

 

In all my WOT runs, I see between 3-4 degrees more ignition advance across the rpm band, all testing variables kept as consistent as possible. Part throttle runs show a similar difference, but of course there's a bigger range in the data points due to small inconsistencies in throttle % from run to run.

 

As the manager of a laboratory engine test lab this is incorrect.
Premiums do contain higher concentrations of cleaners and they do not contain diesel fuel components.
Diesel fuel burns hotter only because of the very high compressiowhen lighted off.
All gasolines have about the same amount of unburned hydrocarbons so there is no difference.
Premiums generally have more energy from the heat of combustion due to better and more components like toluene.
But yes, burning premium in a Fit is a waste of money unless you're on track.

 

I have to use the good stuff because of added boost, and will just sit this one out.

 

i never said premium has diesel in it i thought products such as fuel injector and fuel system cleaners had it in it as well as detegents i guess i was mistaken.

I guess I also mis-stated...diesel has a much lower octane than regular gas, correct? which is why it combusts without spark and under high compression (which generates the heat necessary to begin combustion), whereas if you were to use regular gas it would not combust properly, if at all in a diesel engine. Correct?

So as far as I understand octane rating is (in its simplest explanation) resistance to burning, or rather...the speed at which the gas burns. This is why we use higher octane fuels in boosted or high compression cars...so that the combustion happens at or slightly after TDC therefore preventing "knocking" which is detonation BTDC due to excessive pressure in the cylinder causing the faster burning or "Easier" to burn fuel to ignite prematurely.

Just following this logic it seems that the "slower" burning 93 octane fuel would leave more unburnt leftovers than the "faster" burning 87 octane. But I guess that is incorrect? I know for a fact i've seen richer AFR's in NA cars running 93 than cars running 87...my mustang actually for example at wot had about .7 richer afr running 93 than it did running 87. At normal cruising tho, it was unaffected (88 mustang gt with headers, side dumps, built tranny and differential 3.73 ratio, msd cap, coil, ford motorsports ignition wires, and stock heat range iridium plugs if it matters). Can you explain why this would happen? (i love having real car discussions on a forum not just "which intake is better?? and other nonsense like that lol)

 

An 88 mustang used a vacuum advance that provided advanced timing in conjunction with the centrifical advance..... At wide open throttle manifold vacuum drops and timing is advanced to a lesser degree and all of the fuel isn't burned..... Advancing the timing for additional advance will allow more of the fuel to be burned and produce more power and better fuel mileage..... Honda ignitions automatically compensate for fuel octane and adjust the timing accordingly..... Read the owners manual and you will find that Honda does not say to use 87 octane fuel, but not to use fuel with an octane rating lower than 87. The under square bore and stroke plus 10.4 compression ratio and ability to increase or decrease timing advance via the ECU is going to burn fuel with much higher than 93 without causing problems......People in other parts of the world have been using 97 octane and higher in Fits and would never think of using anything else.

 

You have documented a measured 3-4 degrees more ignition advance with premium vs regular gasoline. The question, still to be answered, is whether this extra ignition advance results in a corresponding increase in horsepower; intuitively, this makes sense, but until we see controlled dyno results on a Fit engine, the question remains unanswerable, except by seat of the pants testimonials.

 

ok fantastic so that verifies my theory that a car without ecu controlled ignition advance will burn the 93 octane at less efficiency than 87 unless the ignition is advanced manually to compensate for that. I thought I was going crazy lol thank you.

I'd really love to see some dyno results with 93 octane vs 87 octane in a fit...I'd even more so love to see the same comparison but with a hotter plug than what came from the factory, as this should (in theory) make even more power. I know advancing the timing on my mustang3-4 degrees makes anywhere from a 15-20hp difference, depending on the day. Granted the fit isn't going to see as inflated results due to the overall power being less...but if we can pull out an extra 5-7hp using simply plugs and fuel? that'd be pretty great.

 

I don't think that people would spend money on products to increase advance if there wasn't power gains measurable on a dyno.... If a person can feel an increase that is satisfying to them, why should they spend money for a dyno run? ..... If you can not feel a difference and experience an increase in fuel mileage that at least somewhat offsets the expense that is great.... You can buy a 20 ounce Coca-Cola and have a little change left in your pocket when you fill your tank.

 

Leaving aside the economics of soft drinks and bottled water, I would argue that history shows that this sort of behavior is exactly what people do. "People" waste millions, if not billions, annually on exactly such seat of the pants evidence. "I washed my car today, and I swear, it feels faster." "I just installed Weathertech floor mats, and I can't believe the performance difference."

If you have spent money on something, it's much easier to persuade yourself that it resulted in a positive change than not. The past 100 years of the auto industry is littered with examples of miracle products that do nothing but lighten your wallet.

 

...are you saying that my super cool electric computer fan supercharger i bought on ebay is a scam?? whatever shall i do????

</sarcasm>

...lol sorry, i had to.

 

I guess that type of reasoning would also apply to my KraftWerks supercharger also.

 

Premium gas is 10 percent denser than regular gas and has less ethonal in it which will give you 5 to 13 percent better gas mileage than regular. An engine has a certain timing curve built into the computer and with v-tec there is a few timing curves in there. Timing and fuel trim is corrected by the oxygen sensors signals to the computer using a correction map in the computer. That is why your check engine lite dont come on because there is a correction map when using premium. Octane really has nothing to do with timing in the past car mfg. would take out a few degrees of timing so the engine would not dentonate it self with lower octane. Fuel air is the problem now the computer is set for 14.7 most of the time and 13.2 to13.6 max brake torque. New cars run in close loop timing even at full throttle. The additives in premium also coat the engine with a slippery coating which slows the formation of carbon deposit and keep the engine cooler less friction. Certain Racing fuels could run in your car with out any adjustment but the lead would ruin the oxygen and catalitic converter in a few hours. Most unleaded racing fuels you need to add more fuel and timing because of more fuel. The 2 dollar a week more for Premium gas is cheaper than the money 3 dollars I would have to use in buying Regular plus there is better power and cleaner oil and better driveablity in all driving situations.

 

You're going to need to back this up with some citations.

The only difference between premium and regular gasoline is the octane rating. The amount of energy, gallon for gallon, is the same.

Ethanol raises octane (and lowers the energy content). Premium gas may actually have a higher octane rating from more Ethanol and less energy content in a funny turn around...

The octane rating is a measure of a fuel's ability to prevent pre-ignition (knocking) that often occurs in a performance engine due to higher compression, increased fuel/air due to turbo/super charging.

Pre-ignition is exactly what it sounds like, the fuel is igniting before the spark ignites it from heat/compression alone.

The only reason to use premium fuel is to prevent knocking in high performance engines (unless your fit is turbo charged, I don't think you need to worry).

references:

octane

more

ethanol

more on ethanol

 

The api gravity of regular gas is around 60 and premium is 55 and #2 diesel is 42, the lower the number the more energy there is per gallon. 10.4 is on the high side of premium. in Europe they have 96 rm octane and run up 11.5 to 1 compression. There is more ethonal in regular to raise the octane from 82 octane base fuel and the chance of fuel seperation is greater the more ethonal used.N- Octane (straight chain)has the same 8 carbon and 16 hydrogen -18 octane rating as Iso-Octane with 100 octane. All I am trying to say is there is a differece between regular and premium and if you have ethonal in your gas there is a noticably better performance and gas mileage. When ethonal makes it to other states there will be alot of problems esp with mileage and driveability.

 

I drive 54 miles every day and get 40 mpg with premium when gas was high I tried a few tanks of regular and my mpg dropped to 35-36 so I will continue to use Premium. There is more to gasoline then octane, also there is a difference between brands. In the winter My aveage drop to 37 mpg and 33-34 with Regular. My wife van gets 18 mpg with regular and 24 with premium. I got over 27 mpg on Highway this summer with a fully load van and drove over 600 miles with premium in a van that was only to get 24 Highway with the required Regular. per computer in van.

 

Source: USATODAY.com - Why use premium gas when regular will do?