93 or 95 Octane? - Page 2

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  1. #21
    Join Date
    Jun 2012
    Thanked: 1052

    Default Re: 93 or 95 Octane?

    Quote Originally Posted by MariusFourie View Post
    Yes, hence my statement that if the car cant adjust parameters based on fuel characteristics, the benefit is minimal.

    Old school cars will adjust timing based on temperature and map/maf and/or tps.

    New school cars use oxygen sensors and knock sensors and based on the octane, the knock and combustion will be different and the ecu can adapt timing and fueling for it, giving you benefits.

    If you dont have the sensors, how will the car know the fuel is different and adapt?
    Yes the car will run slightly different on different octanes (with dumb ecu control) but the true benefits come from oxygen and knock sensors helping the ecu to optimize.
    Benefit of running 95 in a car designed for 93 is not minimal, its zero but with the added cost of paying more for fuel.

    What the engine management and sensors allow is for a car designed for 95 to be safely run on 93 without engine damage by retarding timing and playing with fueling at the expense of performance and fuel consumption.

    If the engine is a low compression design engineered for 93 then there is nothing the management can do with fueling and timing that will extract the benefit from 95 over 93.
    Nothing screams "Bad workmanship" like wrinkles in the duct tape

    2012 Q7 4.2 TDI
    Birkin SR20VET race car

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  3. #22
    Join Date
    Nov 2007
    Thanked: 2841

    Default Re: 93 or 95 Octane?

    Quote Originally Posted by MariusFourie View Post
    That's very helpful. Thanks!
    Sorry were out of office the whole day.

    What Mullerza said. Some high performance engines have chambers specially designed for high octane fuels.
    Even if the ECU cut back timing it can be damaged by lower octane fuels. Some modern engines run up to 12:1 compression ratios. Same with special purpose designed petrol turbo engines will definitely have a loss in performance when using lower octane fuels than what it is designed for. The ECU will cut boost the moment it detects knock.
    It is not what you buy its what you build.

  4. #23
    Join Date
    Apr 2014
    Thanked: 3497

    Default Re: 93 or 95 Octane?

    Am I right saying that instead term "high performance" we should consider "high compression ratio". You do not want pre-ignition. Basically you need fuel that doesn't fire on its own "knocking". Modern engines prevent this in some ways as far as I know. Pre-ignition is no good if the piston is still going "up".

    Old school says "waste of money" to use higher octane than specified. At the same time lower octane than specified is damaging the engine.

    New school people be free to reply.
    2003 Grand Cherokee 4.7l
    2012 Smart
    Never drive a normal car 8)

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  6. #24
    Join Date
    Apr 2011
    Thanked: 211

    Default Re: 93 or 95 Octane?

    Have tried both 93 and 95 octane in both my vehicles and 95 gave me marginally better milage on one of them, made no difference on the other. Didnít really feel any benefit or downside in terms of performance on either vehicle.
    '06 TJ Wranger | 4.0L Auto| 4.5" Lift | 35" Copper STT | 15" MT Classic II Black | 4.88 Gears

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