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Discussion Starter #1
I know that the mz3 doesn't need premium fuel, but is it okay to use it? will I get any performance out of using premium(91) or even super(89) fuel?
 

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From what I have been reading and been told by the dealer that useing the higher grade fuel will not do anything for you.
 

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Some MZ3 owners who used 91 and above had problem with their cars.
So I suggest using the recommended one, which is 87, regular unleaded.
I know we love our cars, but this is not some kind of high-performance car that need premium fuel :)
 

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Although I agree to put regular 87 octane gas (which I do) , I have just been thinking though with all that crappy cold weather.....would a high octane gas start or ignite more easily?
 

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Although I agree to put regular 87 octane gas (which I do) , I have just been thinking though with all that crappy cold weather.....would a high octane gas start or ignite more easily?
No, high octane is NOT easier to burn. In contrary, in the cold weather, some premium-fuel engines can even uses regular gas without compromising the performance.

Here is few externall tendency suitable for low-octane use: cold weather, high altitude, low load.
 
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running anything higher than 87 octane in these engines will not give more power, and may actually hurt performance. Many of the Mazda6 owners with the 2.3L and 3.0L have tried to run 91 octane. They all experienced a rougher running engine and even lower horsepower on a dyno.

We will have to wait until we have a way to tune the computer for higher octane fuel. The benefit to this is that we will then be able to run 91+ octane and get more power. If the 2.3L has 160hp now on 87 octane, I would expect to be able to get 170hp on 91 octane and some engine tuning.

Nikolas
 

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its the ignition system that cant fire the higher octane. altitude affects how high octane you can run. the air is thinner, and since an engine is an air pump, not enough air and higher octane fuel makes it hard for the engine to combust fully.
 

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I think Draxas is correct in saying that running premium gas may actually hurt your engine. I'm not a chemist, but my understanding of gasoline is that octane levels are not an indication of power output. It's a percentage of octane (as opposed to heptane) molecules. In other words, 87 octane actually means that the gasoline is 87 percent octane - 13 percent heptane (or some other molecule). The more octane the gas contains, the more resistant it is to spontaneous combustion.

The power aspect of the gasoline comes into play when using an engine with a high compression ratio (high being above 11:1 for example). Using 87 octane gas in an engine with a compression ratio higher than 11 could result in engine knock - very very bad. High octane gas is much harder to ignite, thus the chances of engine knock are greatly diminished.

I'm not sure tuning a computer would allow the engine to burn 91 octane more easily. The only way to burn high octane effectively is to increase your compression... can you do that by tuning a computer? I would think you'd have to get some after market pistons or increase the length of the stroke. I could definetly be wrong about that though! Does any of that make sense?
 

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I'm living proof that the higher octane will hurt the engine. I'm willing to bet money that's why I'm having an ignition problem (won't turn over easy), as well as a serious issue with carbon residue on my exhaust tip. Just this week (since I had my battery replaced by Mazda) I also noticed that my idle is very hard - RPMs are good, just rough.

I am around 950 miles, and on my fourth tank. First tank dealer filled (most likely 87). I put 89 in the second, and 91 in the last two before putting all the parts of the puzzle together.

I'm going to try and run this tank dry, then fill 1/4 - 1/2 with 87, run dry, then go all the way back up with 87. The car just isn't tuned to do anything with the extra bits that higher octanes provide, and it will leave serious residue throughout the system.

Excuse me if this is confusing, but I'm also drinking right now. :)
 

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edit: MetalCord's explanation is "ALMOST" EXACTLY correct.

edit: I am also drinking right now... Cheers!

This part is definatly correct:

The power aspect of the gasoline comes into play when using an engine with a high compression ratio (high being above 11:1 for example). Using 87 octane gas in an engine with a compression ratio higher than 11 could result in engine knock - very very bad. High octane gas is much harder to ignite, thus the chances of engine knock are greatly diminished.

THis is why most turbo/SC cars require 91+ octane fuel, most forcefed engines have high compression ratios.
 

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MetalCord said:
It's a percentage of octane (as opposed to heptane) molecules. In other words, 87 octane actually means that the gasoline is 87 percent octane - 13 percent heptane (or some other molecule).
octane level is not a percentage of anything (how would you explain 110 octane racing fuel?)
octane = anti-knock index
 

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how would you explain 110 octane racing fuel?
But my owner's manual says to use 87...

You must be incorrect in your racing octane number..
 

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I have clear few things out here.

- Octane index measures the antiknock of the fuel (how hard the fuel can be auto ignited under high pressure/temperature).

- The "octane" term is used for history reason. The reason is fuel with more octane molecule (8 carbons) are harder to be detonated. Now a day, octane index does not even correlated with the proportion of octane molecules. People uses non-petroleum based additive to enhance the octane index (e.g., the old method is addling lead, which don't change the octane molecules)

- Octane index is measured by a special engines, and the numbers (both Motor and Research index) are empirical and do not reflect the percentage of octane molecules in fuel.

- Yes, the ignition timing (and not only the compression ratio) can have an impact on the octane requirement. That's how the anti-knock sensor works. When the knocking is detected, the ECU RETARDS the ignition to prevent knocking. You might justly ask the question why RETARD, when the auto detonation happens too early. This is a thermodynamic effect. When the timing is retard, the combustion gas burns and expands while the piston is pulling out. The gas don't work againts the piston, therefore the compressed combustion reach lower temperature, and knocking won't happen. Just like a squash player wait too long for the ball getting away from him before smashing it. (and the player becomes very inefficient in smashing the ball, just like the engine).

- As for using higher octane could hurt the engine. Personally I don't buy it. I have read serious research paper on the topic, and the conclusion is: "not significant" (I was engineer for an oil related company). With all due respect, I don't think anyone out there have a resource to quantify correctly the effect of octane index on engine power (take many samples of fuel, analyze the fuel, make sure the experiment equipment work correctly - a car on a dyno does not qualify, and all other conditions are unchanged from experiment to experiment).
 

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Discussion Starter #15
What if you messed with the ignition System (Performance spark plugs, ignition amplifier, plug wires) or the intake system to allow more air into the engine? would the car then be able to tolerate higher octane?
 

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IMO the only way in taking advantage of higher octane is:

- increasing the compression ratio and change the ECU
- add the turbo (the ECU should come with the turbo)

You must increases the pressure and temperature of the combustion mixture then think about optimal ignition. Ignition alone is not enough.

Now if the intake can take more air, it could increases a little bit the pressure of the combustion. But remember, car makers recommends the regular fuel even for hot summer at sea level. So unless you runs your car under this extrem condition, I bet the premium gas would help.

BTW, notice that Mazda recommends to use 87 octane gas OR HIGHER. That means Mazda3 engines can tolerate higher octane gas (albeit wasting money).

One last comment. Even that US government requires a minimum amount of detergent in all type of gas, some oil companies (e.g., Chevon) advertises they put more detergent in high octane gas. So for those you drive many short trips in the city, where the carbon build up is favored, it might be wise to fill a premium gas tank (make sure it have indeed more detergent) now and then in order to clean the cylinder.

Bruno
 

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DJ Spencer said:
how would you explain 110 octane racing fuel?
But my owner's manual says to use 87...

You must be incorrect in your racing octane number..
i dont think you understood what i said
im not saying to put 110 octane fuel in your 3...
 

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Could you just advance the ignition timing to burn the higher octane fuel more effectively? If the ECU is set for 87 octane, and that the knock sensor is used to adjust timing, it will not "know" that higher octane gas was used since there is no knocking.

The idea seems reasonable...I don't really know much about engines...just bits and pieces from different automotive forums. So, there is a good chance that I am wrong. :p
 

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Could you just advance the ignition timing to burn the higher octane fuel more effectively? If the ECU is set for 87 octane, and that the knock sensor is used to adjust timing, it will not "know" that higher octane gas was used since there is no knocking.
The timing is computed optimally by the OEM ECU for the factory compression ratio (10 for N/A 2.0L and 2.3L).

- If you advance the timing on the current engine, you go away from the optimum point, regardless what type of gas is using.

In order to take an advantage of the high octane: you need TWO things:
(i) increase the compression ratio (or add a turbo)
(ii) change the ECU, that will recompute to the new optimal timing for the higher compression ratio (more advanced than the old timing).

There is no short cut here, unfortunately.
 
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