Will octane booster improve power in XV?

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Thread: Will octane booster improve power in XV?

  1. #1
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    Will octane booster improve power in XV?

    I use 91 fuel and live above 6000 feet over sea level. I own a 2016 XV still under 1000 miles old, it drives beautiful no complaines, but a bit more of power will be wellcome. Since I can only get 87 and 91 fuel around here, I want to try an octane bosster like Royal Purple, any advice on this matter will be wellcome, hapoy sunday.

    Some forums say it is a waste of money, others say it does make a difference, others say it won't work unless ECU is modify.

    I wonder if ECU is autoadjusted depending on different factors that afect engine combustion, like height and octane fuel among others.

    I know my answer will come when I actually try it, I have made a research about octane boosters and Royal Purple is the one I want to try, unfortunately local autozone won't have it until mid april, so until then I can only guess.
    Your own experiences will be wellcome

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  3. #2
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    Depending on what you were driving before you got your Crosstrek is where you draw the line as far as wanting more power. Former 2004 Subaru Forester owner (EJ 2.5 liter 175 HP). I'm with you, I feel the car needs some more horses for its weight. There is no fix in a bottle...more displacement or turbo (bigger engine) is all you can do.

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    Higher octane does not create power in an engine designed for lower octane. Higher octane simply ignites at a higher pressure, which is useful for high compression and turbo engine to prevent pre-ignition. So running a lower octane fuel in an engine designed for higher octane will result in pre-ignition, pinging, and loss of power (although modern engines can retard timing to compensate, the loss of power will still be there). But running a higher octane than needed simply drains your wallet.

    Also, the octane booster bottles do not actually help increase the octane to any significant degree. I read somewhere that you need something like a gallon to boost octane by 1 point.

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  6. #4
    At 6000ft, 85 octane will perform as well as any higher octane. The only performance improvement from higher octane would come from a lighter wallet.

  7. #5
    Senior Member AWDfreak's Avatar
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    Unless you like to needlessly drain your wallet with the highest octane available at a fuel pump, IMO just run what the engine is designed for, 87 AKI or higher. Higher octane means it is more difficult for combustion to occur, not necessarily more power. The increased output only happens with engines designed for higher octane fuels.

    For increased power output, you'll have to look into an upgraded engine tune, which changes the fuel mapping of the ECU, then you can begin to think about taking advantage of higher octane.
    "Why would I want to profess my feelings for some 3D girl?" - Tomoya Aki from the anime Saekano

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    Quote Originally Posted by sputnik767 View Post
    (although modern engines can retard timing to compensate, the loss of power will still be there)
    This is my hope, that FB20 engine is still compensating and I can get a few more horses with liquid booster.
    Thank you all for your kind answers

    As soon as possible I'll try Royal Purple booster and post here any result, that in the worst of cases will be 15 bucks wasted

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    First of all, at best you are able to measure a subjective power change ("it seems more powerful"), which is highly variable depending on weather conditions, temperature, humidity, gasoline quality, as well as your own prejudices. This will make for a worthless, extremely variable, and unreproducible study given the number of variables that you can't control for.

    Second, as per a reply above, the higher in altitude you go, the lower octane fuel you need. I am assuming this is true as I don't know enough about it to claim otherwise. Therefore your engine would not be compensating by retarding timing, as the octane rating is technically higher than you need. The engine does not adjust for octane as the ECU has no way of knowing what you put in. It will adjust if it detects pinging (pre-ignition), but unless you have pinging, no adjustment is being made regardless of the fuel. I believe that excessive pinging should trip the check engine light as well, but I am not 100% sure.

    Third, even in the extremely unlikely event that you notice an actual improvement that is measurable and reproducible, $15 extra per fill-up would increase your fuel costs by 50-60% per year, in typical US prices.

    I am assuming that you are having issues with power for mountain driving. I can tell you from personal experience that it is plenty powerful enough for the mountains that I have driven across, but I have never crossed the roughly 3,000 ft elevation mark. If it is truly inadequate for you, I would recommend trading the car for something else, because there is nothing that can reasonably be done to this car to improve power in any significant degree. Not even the tune that some people have talked about. So either live with what you have or get something else. But don't waste money chasing power gains.

  10. #8
    It's high performance engines designed to get the most out of premium that can retard timing when a microphone detects pinging using regular. The Crosstrek engine is not such an engine. It is an engine designed for economy and tuned for regular. That's 87 octane in the USA at sea level. Get above about 5000 feet and the lower atmospheric pressure means enough fewer molecules of oxygen are getting stuffed in the combustion chamber to make 85 octane handle the roughest conditions the engine will see. Higher octane won't add any power and is just a waste of money.

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  12. #10
    Quote Originally Posted by Roberto Watson View Post
    I use 91 fuel and live above 6000 feet over sea level. I own a 2016 XV still under 1000 miles old, it drives beautiful no complaines, but a bit more of power will be wellcome. Since I can only get 87 and 91 fuel around here, I want to try an octane bosster like Royal Purple, any advice on this matter will be wellcome, hapoy sunday.

    Some forums say it is a waste of money, others say it does make a difference, others say it won't work unless ECU is modify.

    I wonder if ECU is autoadjusted depending on different factors that afect engine combustion, like height and octane fuel among others.

    I know my answer will come when I actually try it, I have made a research about octane boosters and Royal Purple is the one I want to try, unfortunately local autozone won't have it until mid april, so until then I can only guess.
    Your own experiences will be wellcome

    Increasing octane in your crosstrek will boost power, but ONLY if you tune for it. Stock for stock, running higher octane is a total waste of money. Tuning allows the engine to increase timing and extract more mechanical advantage from the combustion cycle due to the higher knock resistance of higher octane, so right now, you're completely wasting your money already. Tuning for it will net you about 10-15 wheel horse power, and better fuel economy. Is that worth it? That's relative to your needs. The car produces about 105 whp as it is stock, so it is a significant figure, but it's not huge. Without a tune you might as well go back to 87 octane though.

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