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all this talk about the compression ratio...my 2018 mustang gt with a gen 3 coyote and 12:1 compression recomends 87 octane in the manual and it runs just fine

i think subaru is trying to cover their asses saying it takes 93 or the far fetched possibility that its basically "tuned" from factory for it which i doubt, or somehow it can't adapt the timing/detect octane or knock, idk, but compared to my mustang it makes subarus engine look sketchy or just sound less reliable period like a ticking time bomb
 

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all this talk about the compression ratio...my 2018 mustang gt with a gen 3 coyote and 12:1 compression recomends 87 octane in the manual and it runs just fine.
If you consider losing about 50 horsepower running "just fine" yep, it sure will. Fords are good about that. It definitely does not RECOMMEND 87 octane. It recommends premium, which mean you CAN run 87. You can typically run any octane you want but you will absolutely get what you pay for. I actually just recently sold my 2018 GT that was roush supercharged. Trust me, if you are running 87 regularly in that car you are doing the car and yourself a disservice. That being said Im pretty confident any modern performance car "can" adjust to run on 87 with all the modern electronics and tuning. But dont expect it to run the same level of performance or even reliability. These little subaru engines are trying to squeeze a good amount of power out of a small NA package. Octane is important. Dont be a cheap ass and try to save $5 at the gas station in your brand new performance car.
 

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tru-boost: idk about 50hp on the gen 3 coyote, only seen an ecoboost dynoed with 87 vs 93 and it was just under 50 at the peak but for the most part was the same until 5k rpms where the 93 kept pulling notably harder. I think boost needs the octane more with the extra power trying to be had though, so i'll call boost a variable in the equation.

I admit I can feel a slight difference between 87 and 93 in the mustang, i have done A/B testing where i ran a couple tanks of 87, ran it dry, then 93, ran it dry, then 87, ran it dry, then 93, and on and on for a season of driving. 93 gave a little more mid-range response and pull, little better off the line, and even some more top end. Overall it felt stronger and it felt like it handled the summer heat better too because it didn't seem to pull timing as much as it got hotter and heat soaked. I also did 0-60 testing on the same road/similar weather with 2.5k clutch dumps and the 93 consistenly ran faster with the same tires and within 500 miles of driving between tests. I can personally vouch it made a performance difference, but not in rush hour traffic...same same there.

No doubt there is a performance advantage. heck i even got over 17mpg vs about 16 by going to 93 on it. but maybe i drove more hills or hit less traffic, idk.

But simply saying because its 12:1 that you can't is not true though. Or that you outright cannot run 87.

Is it a great idea? i'd say no, but that's subjective.

But my mustang has an 18 gallon tank and premium is nearly a dollar a gallon more where I am and I have a 30 mile commute one way to work. So 16-18 gallons a tank, times 3 or 4 fill ups a week (including weekend) isn't just $5. If I can afford it makes no difference though, it's already just a summer toy/summer daily for me so its not a real issue, but I think we can at least agree that you're leaving some performance on the table - how much, well you can pay for the dyno time and I'll bring the car. If its worth it is still up to the individual to decide based on their use case. Though I really don't think people should be buying cars they have to ask about things they can skimp on doing. I also don't think the BRZ/86 will lose the same 50hp necessarily but maybe it would; not enough data and no one's done the testing.

EB dyno sheet comparing 93 to 87 on stock tune as tested by Mishimoto. Yes I cannot screencap for shit, i only saved this as a reference for myself.
Rectangle Font Parallel Pattern Paper
 

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If you consider losing about 50 horsepower running "just fine" yep, it sure will. Fords are good about that. It definitely does not RECOMMEND 87 octane. It recommends premium, which mean you CAN run 87. You can typically run any octane you want but you will absolutely get what you pay for. I actually just recently sold my 2018 GT that was roush supercharged. Trust me, if you are running 87 regularly in that car you are doing the car and yourself a disservice. That being said Im pretty confident any modern performance car "can" adjust to run on 87 with all the modern electronics and tuning. But dont expect it to run the same level of performance or even reliability. These little subaru engines are trying to squeeze a good amount of power out of a small NA package. Octane is important. Dont be a cheap ass and try to save $5 at the gas station in your brand new performance car.
all this talk about the compression ratio...my 2018 mustang gt with a gen 3 coyote and 12:1 compression recomends 87 octane in the manual and it runs just fine

i think subaru is trying to cover their asses saying it takes 93 or the far fetched possibility that its basically "tuned" from factory for it which i doubt, or somehow it can't adapt the timing/detect octane or knock, idk, but compared to my mustang it makes subarus engine look sketchy or just sound less reliable period like a ticking time bomb
With the two quotes from above, may it be known throughout the land that if a so called “high compression performance” engine calls for 93 or more octane, it needs it. There may be some rare miracles where 87 will get you to the grocery store below the speed limit with no noticeable knocking from the engine. Fair enough. But getting on it, going up steep grades? It’s gonna knock.
Then…. There are some performance naturally aspirated engines that aren’t (or weren’t back in the day) which weren’t high compression. Even though they had a hell of a lot of hp. Like some older Corvettes. They’d run an regular but just not as responsive . No knocking, no damage.
And… there are engines like my 3.6 V6 natural breathing port injected workhorse of a Chrysler engine in my Avenger. It is made for 87 and is flex fuel capable. It gives 283 hp on any gas. Do I run 87? No I do not. I run mid grade and then 93 once a month for the extra additives from Mobile. But it’s not a High Compression engine. It’s a 6 that just has DOHC with not even direct injection. And it screams bloody hell when you get on it. Gas mileage not so great when doing so .:)
Point being…. High Compression and engineered for smaller displacement and efficiency ….. set up for 93……. Your gonna knock at stress levels. And probably reduce engine life.
 

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Boost is a huge variable. Keep in mind that even with the higher compression ratio in the 5.0 that motor isnt nearly as stressed as that little 2.3.
The SHO Taurus we have as the "family vehicle" right now has gone through a few tunes on various octanes. There are 87 octane tunes for it that make it have more power than when on 93 octane on the stock tune. It "could" make that power but not in any of my dynos. The stars, moon, sun and solar system all have to align with the wind blowing in the right direction for success. The 93 octane tune from unleashed runs like a bat out of hell. When I had any of my mustangs, I cant say I have ever put 87 in any of them. Turbo or not I have to think you would expect AT LEAST 10% loss of power. A stock mustang being 460HP, bare minimum that car is losing 46. I honestly bet more though. Its one of those you totally can do and its not going to hurt anything in a mustang. But why would you? $40k car just to put crap gas in it and not get the performance you paid for seems pretty silly.
These subarus are not anywhere near as bulletproof as that coyote engine either. Boxers have a long history of being very temperamental and sensitive to things like oil quality, gas quality, octane, operating temp, you name it.
To each their own, but Im not spending the money on a toy car then treating it like a civic. Thats just me.
 

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I have 15 mustang 5.0 performance pack with 435hp on 87 octane for 90% commute driving. Weekend spirited drives I run 93 and it is indeed faster. Feels like 10-15hp stronger not 50. I don’t think an 18+ mustang will lose entirely 50hp on 87. I’m slightly disappointed the modern low cost sports car with fa20/fa24 requires 93 but I consider it a constant not a variable.
 

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You guys understand that octane has NOTHING to do with engine horsepower right? It's all about how that fuel has more resistance to detonation that reduces said engine power. I'm no fuel expert... but I did read Wikipedia which states:

"Octane rating" is an index of a fuel's ability to resist engine knock (pre ignition) in engines having different compression ratios, which is a characteristic of octane's branched-chain isomers, especially iso-octane. The octane rating of gasoline is not directly related to the power output of an engine. Using gasoline of a higher octane than an engine is designed for cannot increase power output.
Octane - Wikipedia

Putting 87 octane fuel in a GR86 or any sports car is dumb. Unless the gas station you're at only has regular, quit being cheap & fill the tank up with Premium fuel it deserves haha!
 

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For what it’s worth (I’m assuming no minds will change lol), Honda Civic new gen with a turbo small displacement also requires 93. And that’s not a type R or even an implied sports pkg. Of course , all these “fun” debates will be gone once they all go electric. Although, a major World War is more likely to happen before electric becomes the standard. Meanwhile, almost everything with implied Performance seems to ask for 93 to run well. Curiously…. Here in the States, I saw commercials from Sunoco coming back with 94. It went away for about ten years . Now it’s a tv ad. Go figure.
 

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You guys understand that octane has NOTHING to do with engine horsepower right? It's all about how that fuel has more resistance to detonation that reduces said engine power.
You are spot on that higher octane is needed to prevent knock with high compression and forced induction. But you cant say it has NOTHING to do with horsepower because it absolutely does. When you run low octane fuel in a high performance engine you will experience knock. The direct result of that is that the ECU will tell the car to pull timing and in some cases run more rich as well. Pulling timing and added fuel will result is huge power loss. In that case I would say the low octane was the cause of the power loss. Or at the very least say that the power made was variable based on the octane used. The ford ecoboost engines are INSANE how much of a difference octane makes.
 
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