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Discussion Starter #21 (Edited)
Do what makes you feel better, but this is mostly a placebo effect. Premium gas and reglar both have a required level of detergents. Shell will advertise additional detergents, but look into it and you will find little support for using the additional additives. The only real benefit to your fuel choice is the ethanol free part.

While I don't think it is a concern for the XV, I know for a fact that the quality of fuel for the same brand and same octane level can vary by gas station. I used to swear by Shell 93 octane in my Focus ST. I moved to a different city and my data logs showed the car was pulling a little timing. Switched to BP 93 octane and problem solved. Did a little reading and found out from reputable tuners that quality variations like this exist.

Paying a Premium for High Octane Gasoline? | Consumer Information
I use Chevron myself, mainly because of the Techron in it, for keeping my injectors and valves clean. It's also a Tier 3 fuel. I've used Shell on occasion, when no Chevron station is around. Sadly, I don't know of any gas stations here in the NW which sell fuel w/o any ethanol in it. Ethanol is a complete waste of money. It kills both your mileage and performance, and when it comes to the environment, taking into account the pollution created in it's manufacture, the advantage(s) is canceled out.

I not only read that Techron is the best to use, when keeping your fuel system clean, but talked to mechanics, including those who work for Porsche and BMW, who said likewise. I haven't heard anyone have anything bad to say about using Techron, or say that it doesn't work. As for what Shell uses, I can't comment there, other than they do use detergents.

On the other hand, I won't ever use Arco. I've known people who used nothing but Arco, and had issues w/their Injectors eventually giving them problems. After having them cleaned, everything was back to normal. I've told them to stay away from Arco. From what I've heard, Arco has either no detergents in it, or very little, which is what makes it cheaper to buy.
 

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On the other hand, I won't ever use Arco. I've known people who used nothing but Arco, and had issues w/their Injectors eventually giving them problems. After having them cleaned, everything was back to normal. I've told them to stay away from Arco. From what I've heard, Arco has either no detergents in it, or very little, which is what makes it cheaper to buy.

Agreed. Arco makes cheap *** gases for the cheapskate masses. Me? I'll passes!
 

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If this were indeed true, then why didn't I feel the same Butt Dyno thing w/my Honda Element, when I ran High Test/Premium in it?
No idea... it is your butt dyno, maybe weather conditions changed that day... maybe your butt dyno calibration was better that day. Essentially you are saying that you didn't notice something with a non-reliable test in one car, but did notice something with the same non-reliable test in another car. You are then arguing that the difference means the test must be reliable. I am sure you see the logical fallacy there. It still comes down to the fact that butt dyno testing is not extensive and proves nothing.

Once again, the ECU in the Subaru can't do the same thing when it comes to running High Test/Premium on the 2.0L engine, as in the ST's?
Could the XV ECU boost timing and add power on higher octane fuel? Yes... Will it? I doubt it. The only way it would add timing is if it were previously removing timing due to a knock event on regular. Since it is designed to run on regular, knocking should not be significant in most cases. Personally, I would only run premium in the XV if I were having issues with knock. I would only expect knock issues in the XV if there was a problem with the engine or if the XV is being used in a severe environment (exceptionally hot weather, towing, etc.).

Since you bring up the ST adjusting power on regular versus premium... In the ST, running regular has 0 peak torque penalty and only 10 HP (peak) loss (so 252 HP on premium and 242 on regular). If you look at a dyno for an ST on regular versus an ST on premium you see that the power loss is only higher in the RPM range (starting around 4K). Essentially this means the power difference is only noticeable on the ST (a Premium Recommended car) at full throttle. Yes regular versus premium dyno graphs exist for the ST, so we don't have to worry about speculation on the ST unlike the XV :tongue:
 
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The XV Crosstrek was engineered to run on 87 octane, it will not hurt it or give you any future maintenance issues if you use the gas it was engineered for. It will also not help you in any way to use premium gas, no horsepower gain and it won't clean your engine anymore than regular gas since nowadays it has additives also so it won't make your valves dirty. The only downside to using premium is the cost, with it being 20-40 cents more in a fifteen gallon tank that's $3.00-$6.00 wasted. With that being said I still use premium gas for everything, I even put premium in my weed whacker!! I like to use Sunoco or She'll gas only too, none of that cheap stuff. Maybe I do it for peace of mind idk. My problem is the ethanol they put it gas it's not good for my older car, but the Crosstrek is good for it. Maryland only has three gas stations in the state that doesn't use ethanol so it is hard to come by.


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Ok...there’s a noticeable difference from Regular to Premium. I ran Premium in my FRS and my BMW 4 turbo. I purchased a brand new 2019 Limited Crosstrek and went by the book and what did I get? The a typical lag, slow, underpowered Trek we all have heard about. I got tired of it and went to the best around my parts, 90 octane, non-ethanol. I dont know how they blend in these parts but the difference was noticeable. Start, idle, smooth as silk. Took it to the road and what a difference...I had power. Response off the line is better. Passing on the highway, sure with no worries. I kid you not and I’m an old schooler willing to put up a challenge. I say premium does a heck of a job in getting those ponies out and I have seen a mpg increase. From 28 to 31 highway. I’m sticking with premium because it works. I agree, use premium in all your yard equipment otherwise you risk deals, floats and a bad run.
 

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Ok...there’s a noticeable difference from Regular to Premium. I ran Premium in my FRS and my BMW 4 turbo. I purchased a brand new 2019 Limited Crosstrek and went by the book and what did I get? The a typical lag, slow, underpowered Trek we all have heard about. I got tired of it and went to the best around my parts, 90 octane, non-ethanol. I dont know how they blend in these parts but the difference was noticeable. Start, idle, smooth as silk. Took it to the road and what a difference...I had power. Response off the line is better. Passing on the highway, sure with no worries. I kid you not and I’m an old schooler willing to put up a challenge. I say premium does a heck of a job in getting those ponies out and I have seen a mpg increase. From 28 to 31 highway. I’m sticking with premium because it works. I agree, use premium in all your yard equipment otherwise you risk deals, floats and a bad run.
There are many discussions in this forum concerning octane, what is is, why it is, and what octane rating is.

In short, your 2019 Crosstrek has the 2.0 L FB20 direct-injection engine. Subaru upped the compression from the previous stock engine from 10.5:1 to 12.5:1. Compression creates heat. Low-octane fuel can ignite early through the compression stage, which creates knock and poor performance. Octane is added to stabilize the fuel and curtail early ignition. The higher the octane, the greater the fuel can be compressed before igniting. That is why a minimum 87-octane fuel is specified for the the Crossy. All high-compression/performance engines require high octane fuel.

I have a 1976 Toyota with the 20R in-line 4, 8:1 compression. I run 85-octane always, at least when I'm in the high country states, like Colorado. Can't get 85 in low elevation states. Anyways, It would be a waste of money to run high-octane fuel. Wouldn't make the engine run any better, get more power, or get better mileage.
 

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The Australian Owner's Manual states:
"The use of unleaded fuel with an octane rating of 95 or higher is recommended. ... If unleaded petrol with an octane rating of 95 or higher is not available, unleaded petrol with an octane rating of 90 or higher may be used."
I've a CVT, have used both U91 and U95, and the avg fuel economy is best on U95 (8.1 vs 7.6 L/100). Because petrol prices are down right now and out of curiousity I tried U98 and it returned the highest fuel consumption at 8.2 k/L100) Subaru mustn't think much of Australian fuel because a bottle of OEM fuel additive is added at intervals of 15,000kms (9000 miles). My car was just serviced 2 weeks ago and they actually handed me a bottle to add at the halfway point to the next service.
 

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A butt dyno is a butt dyno. Terms such as "smooth as silk", "having power", "better response" and "no worries passing" are, unfortunately, absolutely and utterly meaningless. The engine is characterized by measurable properties, with the only one that matters here being the torque curve. Timing advance might be an indicator of an impact of a different fuel as well, which fractionally translates into torque. Then again - even if the torque were to increase by 5 lbs.ft, that's 3.4%. - undetectable by a butt. Regarding "smooth idle"... well, unless there are measured vibration frequency and amplitude improvements correlated with octane ratings in the exact same temperature, humidity and air pressure conditions, it's not atual data.

As for AUS, it's interesting. 95 RON = 91 AKI. The engine requirement is still 91 RON (87 AKI) but there is no explanation why 95 would be recommended. A possible hypothesis would be that the extreme heat down under favours engine knock well beyond what occurs in EUR/USA/CAN (well, except for the Death Valley), and thus a higher octane rating is suggested so as to compensate. I haven't seen anything corroborating this though.
 

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I'll chime in as we just went to premium(92) from regular (87). Even with 1/2 a tank of premium in it, the car ran much better(vastly improved detonation quality). The mpg has been going up on the computer, but will check with the next fill ups. The quality of petrol here in the PNW seems to be poor. The car would barely run on 87(car would shake at idle at a stop light, quite rough, etc...). The plugs were shot at 12-13k.
I've done octane/mpg experiments(calculating mpg after each fill up) on our other cars(BMW 330xi, Porsche Boxster) and the higher octane fuel here always produces much better mpg(enough to warrant buying it). It will be interesting to see what the 92 octane does, mpg wise, in the Crosstrek over the next few fill ups.
 

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I tow a pop up camper and a kayak, driving up Tioga Pass, a reasonably high pass in California. I tried Premium when towing up the grade. I've also used regular. I've never heard the Crosstrek "knock" with either fuel. I didn't notice any difference in mileage or performance. So I use regular.
 

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Unless the computers in the car are testing the fuel and adjusting the compression ratio somehow, you shouldn't see any increase in performance. The only thing high test fuels are good for are if your engine is pre-detonating / knocking due to the compression ratio.
 

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The XV Crosstrek was engineered to run on 87 octane, it will not hurt it or give you any future maintenance issues if you use the gas it was engineered for. It will also not help you in any way to use premium gas, no horsepower gain and it won't clean your engine anymore than regular gas since nowadays it has additives also so it won't make your valves dirty. The only downside to using premium is the cost, with it being 20-40 cents more in a fifteen gallon tank that's $3.00-$6.00 wasted. With that being said I still use premium gas for everything, I even put premium in my weed whacker!! I like to use Sunoco or She'll gas only too, none of that cheap stuff. Maybe I do it for peace of mind idk. My problem is the ethanol they put it gas it's not good for my older car, but the Crosstrek is good for it. Maryland only has three gas stations in the state that doesn't use ethanol so it is hard to come by.
That sucks about the ethanol free options - I'm in Idaho and have two gas stations near me that offer non-ethanol gasoline. It's all I run in my 1996 motorcycle, and it is what I was putting in my previous 1995 Pathfinder. The bike certainly is a lot happier.

On the idea that premium is a performance mod - it's not. Gasoline is all the same - they only add octane to make it resistant to igniting. The higher pressures in performance and turbo charged engines need this to prevent the fuel from igniting in the cylinder before the spark plug ignites - similar to how diesel motors work. There is NO other advantage to high octange gasoline. If your car doesn't knock on 87, then premium is a waste of money.

Everyone saying they are getting better performance but worse mileage are probably just driving in the higher rpm range of these little engines. I have a 6MT and can beat most people off the line if I don't care about my fuel economy.
 

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Unless the computers in the car are testing the fuel and adjusting the compression ratio somehow, you shouldn't see any increase in performance.
That's literally what the car's computer does. They measure the AFR on the exhaust gasses leaving the engine with the O2 sensor. They adjust the effective compression ratio by adjusting intake and exhaust timing and exhaust gas recirculation. They can also vary the AFR to prevent knock, although that's more for persistent knock.

That said, I doubt there's any noticeable performance gain from running premium in our cars.

Some cars, I don't think our is one of them, can adjust timing so far as to switch between Otto cycle and Atkinson cycle. They can have different effective compression and expansion ratios.
 

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That's literally what the car's computer does. They measure the AFR on the exhaust gasses leaving the engine with the O2 sensor. They adjust the effective compression ratio by adjusting intake and exhaust timing and exhaust gas recirculation. They can also vary the AFR to prevent knock, although that's more for persistent knock.

That said, I doubt there's any noticeable performance gain from running premium in our cars.

Some cars, I don't think our is one of them, can adjust timing so far as to switch between Otto cycle and Atkinson cycle. They can have different effective compression and expansion ratios.
Interesting. When I mentioned the compression ratio I was picturing the geometric ratio - which obviously isn't easily changed. Alternating the timing of the valves due to the 02 sensor data is something I hadn't considered.

First time I've heard of the Atkinson cycle - Thermodynamics failed me. :) Thanks for the response.
 
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