[quote=Texas Coyote;855849]
yeah but it doesn't matter what the compression ratio is at as long as the ECU is tuned for a specific octane.. for example the manual of the honda fit says what? 87 octane and greater... it was tuned for 87 for SURE. I have experience like the both of you except with tuning cars instead of bikes... . and I can see in many cases where tuning to 93 octane will increase like 30 horse power...(or whatever performance increase it gives.. 30 is only an example) ONLY if the car was tuned for that octane... if the car was tuned of 87 octane it will treat the 93 octane as the same as if it was 87 octane. I think thats why in the civic SI manual is almost ALL civic Si generations it says 93 octane and higher.. its because all those cars were tuned to use 93 octane and actually do something with it.. where our car's manual is... 87 octane and.. greater

i mean.. i know i use this example so much... but i seen some serious boosted cars tuned for 87 octane before... its just not as common because if your boosted your most likely looking for the most power anyways so you tune the car according to 93 octane, and you just fill it up with 93 octane all the time.

I wish someone would go ahead and release a tuner for the honda fit ECU so we can all change our gear ratio's.. and tire diameter sizes.. and yes.. even Octane to 93 so that we can end this whole freaken debate on weather our cars can really use 93 octane stock... because if I am not mistaken only few cars can do that stock.. (The Chevy Corvette for example can swap from 87 to 93 octane like 10 years ago.. and even now).

 

Exactly.
I like how this fellow summed it up.
premium fuel vs. regular fuel - Car Forums and Automotive Chat

 

What you and others can't seem to grasp is that the ECU is capable of adjusting the timing and A/F ratio to an octane rating as low as 87..... If you are able to find 100 octane lead free gasoline the ECU will lean out the A/F ratio and advance the ignition timing to run at maximum efficiency with that octane level.....People on other forums all over the world are aware that this car, and many others of other makes and manufacture have been capable of doing this for years as you mentioned in reference to Corvettes..... Please find an official Honda document that states that the Fit is specifically tuned to run on 87 octane because all I have seen in reference to octane is that it is unsafe to use fuel of lesser octane than rating than 87.

 

The information in the article was somewhat dated when it was written in 2005..... Performance chips were commonly used to change timing and A/F ratios over 10 years before this was supposedly written and programmers like those made by Hyper-Tech were available for OB2 systems in 1997.... This I know because I am using them in 2 of my GMC Vortec powered trucks.... I am sending the ECU from my Fit off to Hondata for a reflash on Monday... Cars have advanced a lot since the information on what a ECU system was capable of was compiled for that article.

 

I dont know if people remember when premium unleaded first came out and you but it in a car the check engine lite came on, thats when the ecu does not adjust for higher octane. Cars do adjust. Premium gas has better thermal efficiencies, which means that your car does not work that hard and uses the fuel more economical. Every Car ecu is set to run at 14.7 in closed loop and that doesn't change because 14.7 is the standard for complete burn not max. hp or max mpg. Because of the drive by wire throttle the plate never fully opens, so there is no need for a max hp tune, Honda are very efficient and Honda has the best maps set up in the ecu (from factory). There is a correction feature that adjusts for best operating conditions, 15-20 percent either side of Lombard (14.7) before the check engine lite comes on.

If what some of the posts are true then you could only drive your car on a 60 degree day while it was raining.



When you put an intake and exhaust you change the volumetric efficiencies and the map is wrong so the the correction feature makes a new map Up to +-15/20percent more fuel and stores it long term RAM (random access memory) Short RAM is what the sensors are reading at that moment. You need a dyno to tune a car.

 

Not necessarily a dyno, but many logs..........

 

Some people on this thread are trying to convert lbs to gallons for use in their arguments of energy in octane ratings. Gallons cannot be converted to lbs, and vice versa by using a simple equation... not with any realibility. A gallon of air does not weigh the same as a gallon of lead... a gallon of 87 octane does not weigh the same as a gallon of 100 octane. Rather than try to fudge facts and self-convert, I suggest that you start with the data already in the form of BTU/gal. For reference, my suggestion is:

Gasoline - Wikipedia, the free encyclopedia


And, as I've said before... there is less energy in higher octane gas than lower octane gas.

 

And, as I've said before... there is less energy in higher octane gas than lower octane gas.[/QUOTE]

That is irrelevant when the ECU has to reduce ignition advance and add fuel to the mixture in order to use the stuff..... You really don't get it do you?

 

Regular gas has more energy per pound but weights less than premium(Heavier) per gallon. The problem is that the extra heat produced by regular goes in the cooling system and out the exhaust and not used by the engine. Premium uses all the energy more efficiently. N octane and isooctane has the chemical make up 8 carbons and 18 Hydrocarbons but to different octane -23 to 100 for iso octane. When I ran regular the timing curve is -13 to 51 degrees of timing and when I ran premium -13 to 40 degrees. The more efficient your car runs the less gas you will use. I have also notice when running premium engine runs cooler.

QUOTE from High-perfomance Honda builders handbook by Joe Pettitt
The faster a fuel burns, the more power an engine can make. This is because if the combustion pressure can rise more quickly it has more time to exert pressure on the piston. The flame speed of gasoline is between 35 to50 cm/sec. The actual rate will vary in response to the changing conditions in the combustion chamber with squish areas to increase turbulence.

The flame speed corresponds to a rise in pressure but this rise is not constant because as the pressure rises so does the flame speed. Theoretically, the optimum pressure rise during combustion is typically 20-30 psi per degree of crankshaft rotation from the point of ignition to about 12-14 degrees ATDC. When the crank angle get past 14 degrees ATDC the piston begins to travel much faster thus expanding the volume of the cylinder. This causes the volume to drop even though to fuel is still reacting and creating heat. This gives you a guide to setting timing advance.

However, there is still some power to be gained after about 90 degrees of crank rotation depending on the fuel and type of induction most of the work has already been done. A supercharger or turbocharger combination has more fuel to react so in addition to higher max. cylinder pressures the additional fuel can extend burn time and therefor promote a higher average pressure.

The limit of pressure rise rate for gasoline is said to be around 35 psi/degree of crankshaft rotation and once the rate is exceeded ,detonation is very likely.

 

The ECU will never lean out the fuel to air ratio. Octane is not a measure of the cobustion ofgasoline. The changes iun the injection period is dependent on temperature of the intake air and the profile of the injection based on load required.

 

[quote=Vash;855952]

ECU's are not designed for any particular octane; only the injection required for the load.

 

The ECU is not concerned with octane' it has no idea.
it only concerns itself wiyth delivering the injection period that matches the ECU map of loasd vs rpm and temperature. Octane's only function is preventing preignition which is a function of compression ratio primarily.
There is a small but definite affect from the combustion chamber design.

 

The ecu is programed to MBT 13.4-.13.8 and the oxygen sensor is trying to change it to 14.7 and between them both is to make a new tune. Max. hp power is richer 12.0 to 13.0 A/F. Denser mixture like premium burn faster.

What are we talking about max.hp. or max. mpg.

 

I was looking for some thing to help me explain better and there is not good write up on a Honda website. I found this on a Toyota website How, EXACTLY, does the ECU work? - Toyota Tundra Forums : Tundra Solutions Forum

Also as far as tuning here is a few links

Innovate Motorsports Wideband Air/Fuel Ratio Tuning Very good info

Daytona Sensors LLC - Tech FAQ Engine Tuning


I also ran the numbers from Honda and found out the the Mep pressure is higher on the fit than it is for the civic si that requires premium. The only thing that is different is that civic si engine red line is little higher. MEP=150.8*(torque/cubic inches) Fit is 91.5

The point of this to help some of you understand How a car works. Its all in the math.
In 2008 Honda took a big hit in Horsepower and Torque for the 2007 numbers would be higher.

 

Sorry but I don't understand how buying premium gas dirtys the engine. Honda says to buy AT LEAST 87 octane. They don't say "buy anything BELOW 91".

 

You are correct; high test gas won't 'dirty' your engine. In fact if you knew the formulations you're probably going to get better cleaning of valves from high test than regular. In the old' days of tetraethyl lead for octane improvement high test gas like sunoco would carbon up valves quickly unless you 'cleaned' them regularly by high rpm under load.
Nowdays there idsn't as much energy gain from high test compared to regular but the additives packages are significantly better. In both cases the engines won't show significant cvarboning unless you drive it badly or buy poor gas. A can of non-alcohol injector cleaner once a month is a good practice. And yes I know our chemists say alcohol is no longer a problem of attacking gaskets; I just haven't acclimated. Its ingrained.

 

How a car take advantage of high octane is by the thermal efficiency raising. Using less fuel making the same power. Between 1000 rpm to 2500 the engine is knock limited so the ecu adds fuel and retards the timing at engine loads over 70 percent. I can tell you that most engines operate at loads above 70 percent more often then you would think. So instead of running 11 to 1 the ecu will operated MBT and at 14.2 slightly richer than Lambda during loads over 70 percent. Production Staff So its more like the production emissions that play in that premium is not recommended more. I see at least a 10 percent improvement in mpg and a clean tail pipe with premium over E10 regular.

 

How about different premium brands ? I know that Shell V-Power (91 octane) does not use ethanol at all, but on the other hand Petro-Canada uses tractol (94 octane) WITH ethanol. So this is confusing.

 

I use BP ultimate which I believe is ethanol free. Shell V-power is my second choice. With Shell I lose a few percent in mpg. Bp operates better with less pedal effort than Shell. Shell likes higher rpms with more pedal effort. There is something like 90 different blends in the States and not including Canada and it changes from brand and seasons too. Use what gas gives you the best mpg and driveability to your style of driving.

 

Petro-Canada used to be BP, but I think they use a different blend. I was amazed I felt like I lost a lot of power at lower RPM with Petro-Canada octane 94... Shell V-Power is so smooth... My Fit loves it !