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    Jul 13, 2007 10:09:15 PM

    CuriousOne
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    CuriousOne
    Loc: Chicago, IL , United States
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    100 Octane Gas - How long for ECU to Adjust?

    I have found gas station here in Chicago that sells 100 octane gas. I am wondering what power benefits I might realize with my (currently :-)) stock 997TT on such fuel, and how long (e.g., how many miles, tanks, etc.) it takes for the stock ECU to adjust (assuming the stock ECU does in fact adjust) to higher octane characteristics.

    I would be willing to pay the price differential (which, while quite stiff at nearly 50% over readily available 93 octane, wouldn't really amount to that big an absolute dollar difference in light of how little I get to drive TT :-( ) if there was a resonable possibility of a real gain I could "feel." On the other hand, I would definitely not spend the extra cash to the extent the gain would be more on order of, say, 10+/-hp (which, in this car, seems really only of academic interest).

    Lastly, I suspect that the GIAC, Promotive, etc. 'enhanced' ECUs are able to extract more "go power" from the octane difference. If so, I could save my pennies for the pricer gas once my TT has been properly upgraded (waiting for the tuners' products to 'mature' a bit more before letting them mess with my pride and joy).

    Any experience, insights and/or thoughts on any of these questions would be much appreciated.
    Thnx, Tim

    Jul 13, 2007 11:50:40 PM

    atomic80
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    atomic80
    Loc: Bellevue, WA USA , United States
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    Reply to: CuriousOne

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Tim,

    You're right, ECUs that have been tweaked will certainly benefit more from 100+ octane gas. As a matter of fact, I had the opportunity to try some out in mine. I didn't fill the whole tank with 100+ octane. Instead, I mixed it with some 92 octane gas just enough to make it round off at around 96 octane. Honestly, I didn't notice a difference but that's probably because there wasn't enough of a chance for the ECU to adjust to the elevated octane levels. Who knows maybe the stock ECU programming isn't designed to benefit from higher octane fuel.

    Jul 14, 2007 1:36:40 AM

    AAHTT Offline
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    AAHTT
    Loc: san diego , United States
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    Registered on: Jan 21, 2006
    Reply to: CuriousOne

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Quote:
    CuriousOne said:
    I have found gas station here in Chicago that sells 100 octane gas. I am wondering what power benefits I might realize with my (currently :-)) stock 997TT on such fuel, and how long (e.g., how many miles, tanks, etc.) it takes for the stock ECU to adjust (assuming the stock ECU does in fact adjust) to higher octane characteristics.

    I would be willing to pay the price differential (which, while quite stiff at nearly 50% over readily available 93 octane, wouldn't really amount to that big an absolute dollar difference in light of how little I get to drive TT :-( ) if there was a resonable possibility of a real gain I could "feel." On the other hand, I would definitely not spend the extra cash to the extent the gain would be more on order of, say, 10+/-hp (which, in this car, seems really only of academic interest).

    Lastly, I suspect that the GIAC, Promotive, etc. 'enhanced' ECUs are able to extract more "go power" from the octane difference. If so, I could save my pennies for the pricer gas once my TT has been properly upgraded (waiting for the tuners' products to 'mature' a bit more before letting them mess with my pride and joy).

    Any experience, insights and/or thoughts on any of these questions would be much appreciated.
    Thnx, Tim



    A stock TT needs at least 93 octane (R+M/2), so it might benefit a little from higher than 93 but nothing close to a tuned TT which will develop a lot more power with higher octane, as an example I can tell you that the protomotive ecu tune produces it best numbers with straight 103 octane, although the car runs fine on 91. The difference is readily felt while driving.
    So, a stock car does not need or benefit from 100 octane, save your money till after the upgrades

    Jul 14, 2007 2:09:29 AM

    Moogle
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    Moogle
    Loc: Bay Area , United States
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    Reply to: AAHTT

    Re: 100 Octane Gas - How long for ECU to Adjust?

    I don't believe any stock Porsche can adjust itself to higher octanes higher than 93 (R+m/2 method).

    If you are putting more than 93 octane into your untuned car you are wasting money.

    With ecu tuning/etc, and multiple programs, you will notice a difference.

    Jul 14, 2007 3:16:21 AM

    CuriousOne
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    CuriousOne
    Loc: Chicago, IL , United States
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    Reply to: Moogle

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Thanks for all your responses, which seem quite unanimous. I am now most definitely going to stick with 93 octane until the car has been "properly" tuned.

    Jul 14, 2007 9:43:30 AM

    gradyex
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    Loc: S.F. Bay Area, CA.
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    Reply to: CuriousOne

    Re: 100 Octane Gas - How long for ECU to Adjust?

    If you live in California and only have access to 91 octane (like myself) adding 6 gallons of 100 octane should bring it to 93 and yes, I do notice a difference (2 points). Give the computer a good 15 to 20 minutes to adjust (could happen sooner). Now anything over 93 is a waste and if you already are fueling with 92 you might not perceive 1 point but then again you might? For me there is a difference from 91 unfortunately the 100 octane is $6.50 per gallon and I have to drive 1 hour away (Infinion Raceway) to get it so its a treat when I am in the area (well not for the wallet).

    Jul 14, 2007 11:29:20 PM

    Heist
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    Heist
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    Reply to: gradyex

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Without proper re-tuning of the ECU and mapping, you'll see ABSOLUTELY NO increased performance from 100 Octane gas and end up wasting money for no good reason.

    Nowadays, computers are tuned to use ONLY what they need to perform to the optimum spec that they're flashed with and simply [beep] away the rest. In other words, the engine's performance ceiling is already set to 93. It doesn't recognize 100.

    It's the same as putting 93 Octane in a stock engine that requires 88 ... you'll see no performance gain.

    Now, adding higher octane fuel for better performance was true in the past when computers didn't run engines - it was purely a mechanical process. Put in gas with a bigger BOOM, you get more BANG.

    Jul 15, 2007 4:25:20 AM

    WhoopsyM Offline
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    Whoopsy
    Loc: Vancouver,BC , Canada
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    Reply to: Heist

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Locally, my choices for gas is either 91 from Shell or 92 or 94 from Chevron, needless to say only 94 goes in the car.
    I would have prefer Shell gas but I feel 91 is too low for the turbo.

    Jul 15, 2007 8:25:16 AM

    gradyex
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    gradyex
    Loc: S.F. Bay Area, CA.
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    Reply to: WhoopsyM

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Today i filled my car with 100 octane (14 gallons). After about 10 -20 minutes I felt like I just unleashed the beast in my car. You guys that have access to 94 octane make me jealous. 91 octane is all she wrote in Calif and that falls short of what the turbo was tuned for in North America (no special tuning for California). All of North America gets the same tune parameters. Now using 100 is a waste so at 1/2 tank I will top it off with 91 and still have 94+ octane for another full tank. 100 Octane is only offered in a few locations (these are usually racetracks).

    Jul 15, 2007 9:52:32 AM

    Heist
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    Heist
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    Reply to: gradyex

    Re: 100 Octane Gas - How long for ECU to Adjust?

    For you Californians, instead of spend the extra bread on 100 since 91 is only avaiablle, why not pick up a can of Octane boost and bring it up to 93/94.

    Jul 15, 2007 12:47:07 PM

    RCA
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    RC
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    Reply to: CuriousOne

    Re: 100 Octane Gas - How long for ECU to Adjust?

    According to a Porsche engineer, the 997 Turbo engine adjusts up to 98 octane (which would be 95 octane in the US). Everything above that figure is...USELESS. You may gain 5-15 HP through other circumstances using this fuel but not because the motronic adapts to it.

    To make use of higher octane fuel, you need a new software mapping of the motronic. I know there is a lot of talk about higher octane fuel going on worldwide, we have the SHELL VMax over here in Germany (100 octane which would translate into 103 octane US) but there have been DOZENDS of independent tests in car magazines and scientific publications and NONE was able to prove that there is an increase in HP other than the usual error margin.

    Sorry guys, you can brag all day long about using higher octane fuel but if the motronic isn't programmed to make use of this higher octane fuel, the only thing which is going to get an additional boost is...the content of your wallet.

    Jul 15, 2007 3:00:49 PM

    eclou Offline
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    Loc: Texas , United States
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    Reply to: RCA

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Higher octane will only be of use under the most extreme conditions - repeated WOT like RC's autobahn commute or track laps. Higher octane is only necessary to reduce the chance of predetonation which will lead to ignition timing retardation. Higher octane fuels actually contain less BTU's of energy than lower - 87 octane has more energy in it than 104!

    Jul 15, 2007 3:36:42 PM

    AAHTT Offline
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    AAHTT
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    Reply to: Heist

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Quote:
    Heist said:
    For you Californians, instead of spend the extra bread on 100 since 91 is only avaiablle, why not pick up a can of Octane boost and bring it up to 93/94.



    No octane booster will increase the number by 2-3 points, plus who knows what harm it can do to the engine.

    Jul 15, 2007 4:37:37 PM

    WhoopsyM Offline
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    Reply to: AAHTT

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Most of the octane boosters uses MMT and it's benefits/harms is still debatable. In octane boosters' term, each point increase is 0.1, so a full 10 points increase is needed to raise octane from 91 to 92.

    Would there be a situation where the weather is hot enough that the engine 'knocks' even at the octane rating the ecu is programmed for and needs a higher octane fuel to have normal operation?

    Jul 15, 2007 7:27:48 PM

    JCNPB Offline
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    Reply to: RCA

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Can RC or anyone explain the relationship between octane rating and horsepower/torque for the 997TT? If the factory tuning for the Turbo allows beneficial use of a maximum of 95 octane (R+M/2 method), then how much horsepower/torque is lost if you use lower octane rated gas (e.g., 91)? Is it significant? Thanks for the info.

    Jul 16, 2007 2:16:05 AM

    WhoopsyM Offline
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    Reply to: JCNPB

    Re: 100 Octane Gas - How long for ECU to Adjust?

    If the weather is cool enough that even 91 octane gas is not gonna cause knock, there will be no performance difference, the ecu is gonna run the normal map, but if the weather is hot enough, I would guess the engine would run about 4% less? Just a wild guess based on octane difference percentage.

    Jul 19, 2007 7:28:37 PM

    Scotty A
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    Reply to: WhoopsyM

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Octane has nothing to do with energy or power. It has to do with the antiknock level - how much compression and therefore heat the fuel can withstand before it spontaniously ignites, which causes the 'knocking'. To assume that a 4 point difference in octane is somehow related to a 4% difference in 'performance' misses the whole point. Of course, since the theory behind octane levels is to allow greater compression, which could ultimately result in more power output from the engine, there is a relationship. But it isn't linear with the octane scale, which is just a number.

    Jul 19, 2007 9:31:51 PM

    Heist
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    Reply to: Scotty A

    Re: 100 Octane Gas - How long for ECU to Adjust?

    He has valid point - we all usually make the Octane Rating / Power Correlation.

    Higher octance lets you run higher compression. Higher compression usually denotes a more powerful, performance oriented engine.

    Audi's Diesel R10 of course turns this whole convention on its friggin ear.

    Jul 20, 2007 4:01:06 AM

    WhoopsyM Offline
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    Reply to: Heist

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Not saying every octane point = 1 %, but 91 Octane is just happens to be ~ 4.2% less than 95 Octane. I was just throwing out a ballpark figure.

    Actually the compression in an engine is a constant, not matter how high the octane is or how low, the compression is the same. The octane rating however affects the timing of the ignition, with affects the duration of the power stroke which is where the power comes from. With a lower octane rating the ECU has to take out/retard the timing of the ignition to prevent the 'knock' (pre-ignition ignition), that in turn reduced the duration of the power stroke of the engine and hence lower power output.

    Jul 20, 2007 7:46:03 PM

    Scotty A
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    Reply to: WhoopsyM

    Re: 100 Octane Gas - How long for ECU to Adjust?

    Quote:
    Whoopsy said:
    Not saying every octane point = 1 %, but 91 Octane is just happens to be ~ 4.2% less than 95 Octane. I was just throwing out a ballpark figure.




    Yes, of course. But 100 Octane is just a reference refering to the standard for anti-knock properties of gasoline which is composed of 100% Octane. Adjusting that to 4% less Octane in the mix doesn't mean that the fuel performs 4% better in any other sense.

    You are correct, of course, about the compression and the timing of the engine. The timing is exactly what the ECU manages as it detects the fuel performance. It's a great advantage, as it is only with this variability that the engine can be modified in realtime. Pre-ECU, one had to manually advance or retard the timing for each fuel.
     
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