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Okay, I recently made an interesting observation. I have been using the regular 87 Octane gasoline for my Civic. Some people on this forum have said that there is no difference in using the higher octane. I used to agree, but now I beg to differ. I drove up to Frederick, MD yesterday, with the A/C running. My tank was nearly at empty, the light had been on for a while. Recently my car hadn't been running too well for my liking. I mean, its fine, but doesn't seem to be as smooth as it used to. I understand age has its effects. But in normal driving conditions, taking off from a red light, with the A/C on (Im driving a 5 spd btw) my seems to struggle until about 3500 rpm. Its not a dramatic struggle, just, I almost bog sometimes cause of the lack of power. I put it in first gear, give a tiny bit of gas, as I release the clutch, and then give more gas to get moving, and the gas pedal goes all the way down, but the car doesn't move any quicker. Until it hits that 3500rpm mark, its just a slug.
Okay, I stop at a Sunoco gas station and fill up the tank to full. Instead of the usual 87 octane, and since gas was cheaper up there, I decided to not go with the 87, not the 89, not even the 93, but the 94 that they had. Just for ***** and giggles. Turns out, as soon as I pull out of the gas station, I immediately notice how much smoother the car is running. As I release the clutch, the car almost seems to pull itself. I give it a little gas, and it goes. No more near bogging from stop lights. Its cruising. Did that octane increase help my engine out that much? Also, is it possible for an engine to get used to a certain octane gas, so that if you were to ever go down to a lower one, it would react negatively? Kind of like the once you go synthetic, you cant go back type of thing. Post your thoughts.

 
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hmm they only have 91 where i live.
i think i'll fill up with 91 next time i fill up.

 
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Its all in your mind. The higher the octane the less volitile the combustion. There is no need to retard the combustion in your car, therefore there was no increase. Put it this way, if a drag racer could run ecomony unleaded he would. If you could advance your timing to the point where it pinged, then it would have to be used. The delay in combustion is designed to allow the piston to travel all the way up before the explosion occurs. That why you hear a ping in some cars, the explosion is hitting the top ot the piston before its reach its climax, or on it's way down. You have not altered this piston position so all your doing is getting a weaker combustion and a buncha carbon buildup.

 
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It's all in my mind too. I decided to try going back to a tank of regular gas this week, and sure enough, there is a flat spot when I accelerate. The car does not run as well in general. I have now tried this a few times, and I don't care what anybody says, the car runs noticably smoother and stronger on super. I can hardly wait to burn this tank out so I can get my pep back. I had to literally stand on it to get on the freeway today, not so with super.

So.... Why IS it running better on 91 octane??? The different additives??
I read up a lot on gas, but this has me baffled as well. Now my first honda, an 82 accord hatchback ran like a slug on super and great on regular. WTF????

 
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i just stick to unleaded lol no need for 91-94

 
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Throwing in a higher octance fuel can often cover up warning signs. I know for sure that you can make some engine knocking vanish simply by putting in higher octance gas. The problem still exists. Now here is the tricky part, I had a highly modified Eclipse before this Honda and while it said to take regular gas, with all of the mods, the higher octane actually was noticably better...

 
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what kind of highly moddable eclipse requires regular gas? you mustve been workin with a 420a or n/a 4g63 cuz the 4g63t always needs premium

 
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Yep, it was a 420...but a fast one to boot...

 
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I used to use 87, but now only put in 89 after the head swap. I can feel a difference in the way the engine sounds, but don't know about power. I won't go back to regular tho.

 
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There, its been proving at least 3 times in this thread. Higher octane = Happier car. Its kinda like us human, sure you get a slight buzz off a cigarette (especially menthols), but when you smoke some weed, you get HIGH. Super buzz!

Okay, but really, maybe it has something to do with the way certain people have run their cars, or the modifications each car may have. For instance, I have an aftermarket intake. I know Im sucking in more air than compared to stock. Therefore, the higher octance which is giving me a quicker hotter burn, is compensating for the increase in airflow. Im by far, no expert on the theory of the combustion engine. But wouldn't you agree to that?

Honestly, my car is running so smooth right now, it is quieter, and more silky. Like, my shifts used to be a bit rough at times, cuz of the lack of power from the engine. But now, it feels like the rpms are staying up longer, enough for me to shift and release the clutch. Before it used to drop too low, or just never be right there. But everything feels synchronized in there now. I know this isn't in my mind. I know this because this difference I feel is really noticable. Not just a tiny barely noticable difference.

 
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I remember seeing another Sunoco gas station somewhere out there that advertised 108 octane race fuel at the pump. I think that was just a dream now though, cause I have not been able to find it at all. I searched on the internet as well. No luck. But I wonder what would happen if I used race fuel in my car.

 
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You guys are forgetting that it takes time for the ECU to adapt its self to what ever fuel you are running, so if the car runs good on the gas you've been using for a while, then it will probably run not so good on any other octane... So if you've been runnig 91 for a while then Sure the car will run worse on 87.... same goes if you have been running on 87 and switch to 91+...

Thing is your testing with just your butt dyno... the real proof would be if some one actually ran test on a Real Dyno, and allowed time between gas changes to allow the ECU to adapt.

 
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I'm starting to wonder if the ECU compensates for higher octane gas and changes the A/F ratio and timing just a little?

Supposedly, the Accord V6, 6speed DOES indeed gain horsepower when run on 91. The ECU will compensate. My brother has one, it flies.
I can only guess at it, but the ECU is constantly monitoring the exhaust and tuning for best drivability. So it seems to make sense that better gas would cause the ECU to change the tuning accordingly. Even with bad gas, the ECU in theory will try to keep the engine running at an optimal point, no matter what.

Now I know how engines work, inside and out. But I have to admit that the inner workings of the Honda ECU are still a mystery to me.

I wish someone could clarify this.

But I DO know for a fact that MY car runs smoother, and acelerates smoother on higher octane fuel. I also notice that it cruises easier on the freeway, that I don'thave to push it as much. Now the difference is not dramatic, but it IS noticable. The one thing that positively goes away with high octane in my case, is a slight hesitation and flat spot while acelerating hard, as in getting on the freeway or passing. The car just pulls smoothly like it should. I never tried 100plus octane, only in my truck. It ran great on it. I doubt it'll do much more for the civic than 91. But I may try it just once.

Having said all this, and trying the same experiment several times with the same results, I'm sticking with super.
On a side note, My Mom's 01 auto sedan ALSO runs better on 91 octane. She tried it, and said that it seems to just go by itself. She does not have to "push" it.

So..... any more people willing to try an objective experiment?

 
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You make a great point, and that is what I am wondering about. BUT my car never ran as well on regular as it does on super. I am talking 5 to 6 tanks at a time to see. Maybe the gas in Los Angeles varies a lot. I have NO idea.

But I'd love to see some objective results other than how the car "feels".

 
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My car doesn't run nearly as well on 93 compared to 87. Even if it did, a little more "pep" out of an already pep-deprived car isn't worth the extra $0.2 a gallon.

 
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My head is milled for higher compression, so I'm sure the 89 is better for it. As far as the car adapting, I believe the ecu will adjust the ignition timing according to how the combustion is happening.

 
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The higher the octane, the lower the energy yield. So you'll get lower mileage on a car with high octane fuel if it runs fine on low octane fuel. The only exception is on a high compression engine or one with a lot of carbon build up. You will get pinging and decreased mileage on low octane fuel. Honda Civics run fine on 87 octane. Everything else you've heard in ads that compel you to buy higher octane gas for a Honda Civic is all marketing.