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  1. #1
    kencaymans is offline Porsche Chatter
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    91 octane ethanol free or 94 octane with ethanol?

    I wonder what the general consensus is with other members regarding higher octane gas (94) with ethanol vs 91 octane which is ethanol free.

    I've been running 91 because it is ethanol free, however with all the upgrades done to my car, including Softronicicon. I wonder if going with a higher octane with ethanol will increase power, although I have read that ethanol has a lower BTU.

    Thanks,
    Ken


  2. #2
    Reyk is offline Porsche Chatter
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    Re: 91 octane ethanol free or 94 octane with ethanol?

    I've noticed quite a difference in performance by increasing octane from 91 to 93.25.

    The min octane rating on the Gen2 cayman is 93 octane. Below that I think the ignition advance is dialed back to avoid detonation.

    The most noticeable difference I see is the willingness to rev, starting at about 4000 RPM. With the higher octane it picks up revs faster - again I think due to more ignition advance.

    Out here in California all we get is 91 octane peanut oil. I mix 25% 100 octane with 75% 91 octane to get 93.25.

    I think the extra ignition advance will overshadow the lower BTU of the ethanol.

    Lucky you if you can get 94 octane at the pump....

  3. #3
    talon is offline Porsche Enthusiast
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    Re: 91 octane ethanol free or 94 octane with ethanol?

    Maybe I should confirm before posting, but I was lead to believe that at Chevron's fuel is as follows: 94 octane does not have ethanol the lower grades do.
    I'll confirm this and 2nd post.

    I only use the 94.

  4. #4
    kencaymans is offline Porsche Chatter
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    Re: 91 octane ethanol free or 94 octane with ethanol?

    In Ontario we have Sunoco Ultra 94 with up to 10% ethanol...

  5. #5
    diverdog's Avatar
    diverdog is offline Cayman The Destroyer!
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    Re: 91 octane ethanol free or 94 octane with ethanol?

    I think that the performance difference between 91 & 94 octane is one based on wishful thinking. I'll bet it would be very difficult to measure.
    Daily Driven CS Supercar "Leaps GT3's In A Single Bound"

  6. #6
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    tango131 is offline Porsche Activist
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    Re: 91 octane ethanol free or 94 octane with ethanol?

    ^^^There is definitely a difference between 91 octane and 93 (or 94) octane gasoline. The difference is more pronounced in turbocharged cars, but there is a small difference and the computer in our NA cars over time adjust timing to increase power slightly with 93 or 94 gas.

    To the OP, I believe that ethanol, even though it may have a lower BTU rating the gasoline, actually increases the resistance to pre ignition detonation. Which is essentially all that an octane rating is: the higher the octane rating is, the higher its resistance to detonation. The higher any given fuel's resistance to detonation, the more a car's computer can adjust timing and increase power (to a limit). Bottom line, you're much better off using the 94 octane gasoline with ethanol if making power is your only concern. And btw, this is why one sees some very high-end turbocharged or supercharged exotic cars that are tuned to run on 85 ethanol and produce more power than they would on regular gasoline (i.e., the Koenisegg (sp?)).

  7. #7
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    diverdog is offline Cayman The Destroyer!
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    Re: 91 octane ethanol free or 94 octane with ethanol?

    I don't doubt that the ignition advance in a NA CS will bump up the torque with an octane increase. Just saying that the <1% won't make enough of a difference to matter.
    Daily Driven CS Supercar "Leaps GT3's In A Single Bound"

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