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Thread: What is the best fuel for longevity of the 2.5 Turbo?

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    What is the best fuel for longevity of the 2.5 Turbo?

    I know Mazda says the car can run on either regular or premium octane. I'm not worried about the added HP or MPG. I'm more curious about which octane would help the engine/turbo last longer since I plan on driving this car for a long time. I also buy "top tier" gas and have been using Shells premium VPower since new.

    So, out of curiosity, which octane should make the engine last longer?

    Would regular octane be less stressful on the engine because the engine doesn't work as hard to produce the extra horsepower?

    Would premium be better since it typically has additional additives to keep the engine cleaner? I think the higher the octane the higher compression the fuel needs to ignite, is that added stress?

    Does it matter at all? I'll pay premium to help the engine last longer... I also don't want to be a fool if regular is actually better for the engine overall, lol.

    Appreciate any insight, opinion or science.

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    Registered Member erhayes's Avatar
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    In my opinion there are just too many other factors that affect engine life to try to evaluate which octane is better. The spark plug ignites the fuel and NOT the compression in a gas engine. Your engine will be happy with 87. Ed

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    But happier with 93.

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    Quote Originally Posted by VQ35DE View Post
    But happier with 93.
    Why?

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    Best for your turbo is good oil and regular changes.
    regarding fuel, the car would certainly appreciate higher octane. Up to you if wish to spend extra money.
    Some people will say its not worth it others the oposite.

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    Chevron supreme...but will only increase longevity if you are experiencing detonation on other fuels. On my friendís tuned wrx that requires 91 octane, there was less measured knock on his tuner using chevron 91 than other 91 octane fuels (in California).

    This is the reason I run only Chevron 91 in my ctsv wagon. The cx5 non-turbo just gets the cheapest 87 octane Arco around

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    Quote Originally Posted by Sig cx-5 View Post
    Why?
    Less knock/pre-ignition. It uses the knock sensors to determine the octane in the tank. It dials back on the ignition when it senses knock. If you're running 93 it won't cause knock, and therefor incrementally avoiding wear on the engine. How much wear? Probably negligible. Especially if they're specifying 87 octane as acceptable fuel. I wouldn't have an issue with running 87.

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    For most people in normal driving, I doubt you*d see any benefit in using 93 octane. Unless you*re jamming down the accelerator and running at high rpms, you won*t see the extra HP or get the engine into a range where you*d get knock using only 87 octane.

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    As others have recommended, using a high quality synthetic oil is probably more important than the octane rating. I plan on doing 5000 mile OCI's rather than going out to 7500 miles. Yeah, it's a little more expensive over time but I do my own changes with Castrol Edge 5W-30 and a factory filter for about $35 so not a big deal.
    Using top tier gas is important, they have a better additive package even in the lower 87 octane grade. I plan on adding some Marvel Mystery Oil to the gas tank every 2 or 3 thousand miles, it is good for the injectors and also has been known to keep the fuel level floats operating properly so you don't get flaky fuel tank readings. A bottle of Techron added to the gas tank before each oil change is also a good idea, again we are only talking a few dollars. I worry less about the major engine components than I do the GDI system on this car, keeping everything clean and preventing carbon buildup will have beneficial effects over the long run.

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    Since the engine puts out the same HP and Tq up to 4,000 rpm, it isn't the knock sensor that is controlling the detonation below the 4,000 rpm. Ed

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    Quote Originally Posted by erhayes View Post
    Since the engine puts out the same HP and Tq up to 4,000 rpm, it isn't the knock sensor that is controlling the detonation below the 4,000 rpm. Ed
    What is it then?
    Sigs are visible only in your first post on a page. To change your thread display preferences, click here and enable 'Always Show Signature'.

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    Quote Originally Posted by jcrout7992 View Post
    What is it then?
    A waste of money.

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    Quote Originally Posted by erhayes View Post
    Since the engine puts out the same HP and Tq up to 4,000 rpm, it isn't the knock sensor that is controlling the detonation below the 4,000 rpm. Ed
    You're technically right.. the knock sensor relays info to the ECU, which retards timing to prevent knock. The retarded timing is what results in the 227-hp rating. With higher octane, there is less detonation, so the ECU advances the timing, which results in the 250-hp rating. At least that's how I understand it.

    Fuel is not nearly as important as engine oil and filter, but most will agree that any top tier fuel is good enough. Top tier fuels usually have good detergents in all grades, which will help to keep performance consistent.

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    Quote Originally Posted by Sig cx-5 View Post
    A waste of money.
    That wasn't the question.

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    Quote Originally Posted by jcrout7992 View Post
    That wasn't the question.
    Then what was it?

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