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Ok, so around here, all we get is either 87, 89, or 91. I was just wondering, besides the higher octance levels, does for example 87 octane have less fuel additives and preservatives than let's say 91? Or do they all have the same additives/preservatives, just different octane levels? I use Esso gas, which would be Mobil or Exxon down in the States.

 
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No. Lower octane gas has the exact same detergents and additives that higher octane gas has, provided it's from the same vendor.

 
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Ok cool, thanks

Now if you get 87 octane, which of course is what our cars are designed for, would you get better gas mileage using 91 octane because it will burn cleaner due to its higher combustion properties? Or does it make no difference?

 
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91 burns hotter and with the cat converter so close to the engine, you could screw it up, by having it melt and clog up the exhaust. I personally use 89. I started by using 87, but now that I use 89, I find I get a little better mileage, and the acceleration is a little better. Of course, that's using the good ol' butt dyno, so I could be imagining the accel. part. But the mileage is proven, at least for me. I get about 40 mpg in the city, I used to get 36 with 87 octane.

 
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Actually 91 has lower combustion propertys. Sprisingly, gasoline will spontaniously combust under pressure, how much pressure depends on whats in the gas. Read This

 
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all i know is that i use 89 octane.

Injen

 
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I said the stuff about the cat conv. because of a car that I owned once. It was an '88 Hyundai Excel (quit laughing! ) and it said to use 87 in the manual. But being 16 and knowing jack about cars, I thought that using 91 would help my performance (quit laughing! I know performance and Hyundai don't go together. ) Anyways, after about 6-8 months, my engine started to bog down, and wouldn't rev past 4k. So I took it to a muffler shop, and my cat. had melted in parts inside, and clogged the exhaust path. The guy asked me what gas I was using, and I told him 91. He told me that 91 burns hotter, and that's how I fugged my cat. conv. All he did was use a long screwdriver and a hammer, and cleaned out the cat., so there wasn't a cat anymore (does that make sense). And shazam!! Instant performance (quit laughing! I know it was a Hyundai. )

 
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Sorry, that wasnt aimed at you. I just hit the Submit reply button after you did.

 
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Ahhh So confused, lol. I don't know which to buy now. Like for example, would 91 give our engines any better performance than 87? And about the octane levels and gas mileage, which one gives better mileage, because some are saying this, and some are saying that

 
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Even if there is performance behind it, it wont be too noticable.... but milleage wise, I also have noticed differences.

 
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Yeah true. So do you get more miles on a tank of lower octane gas, or higher octane gas?

 
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probably Higher, but then you have to calculate weather or not the increaced gass milage is a greater savings over the lower cost of the Lower octain gas.

 
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Yeah true.

 
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No worries. It's a funny story anyways. As for your question Majarvis, it probably works out to about the same, moneywise. Spending money on the higher octane, IMO gives better mileage. The cost difference works out to about the same as buying a little more of the lower octane fuel. But like I said above, according to my butt dyno, I feel a little better acceleration and throttle response. Ehhh, go with what you feel is right. Btw, I use Esso gas, if that makes any difference.

 
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Ok cool, thanks.

 
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I got better milleage using higher octane, but like, filling it up, is like... $2 difference from 93 and 89

 
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My mom used to be a manager at a gas station...for anyone that doesn't know
89-cheap
93-expensive w/o much difference in octane levels
91-mix of crap and expensive crap

 
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Use the lowest octane gas that doesn't cause knocking in your engine. For the 7th gen Civic, this is 87 octane. For the RSX-S, it's 91 octane. Always follow your manufacturer's recommendations for minimum octane.

The only difference between the various octane grades is their resistance to detonation/knock (spontaneous combustion under high temperatures and/or pressure). Most high performance engines use high compression setups and/or forced induction. This means more pressure inside the combustion chamber so you need a higher octane gas to prevent detonation.

Many newer models cars can get by w/using lower octane. This is because the ECU's are intelligent enough to retard the ignition timing (operating at less than peak level) to prevent knock. You shouldn't depend on this, though.

Many older cars actually need higher octane gas because over time, deposits in the cylinder walls will raise the compression level, sometimes to a high enough level that you need higher octane gas to prevent knock.

Again - use the lowest octane gas that doesn't cause knock in your engine. Higher octane grades contain the same additives and detergents as lower octane, and their ONLY benefit is increased resistance to detonation. You are wasting $$ if you buy higher octane gas for any other reason. But if it makes you feel better to buy higher grade gas, then more power to you.

 
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Great post! Thanks

 
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I have had my LX a year now and the best milage I have ever been able to pull out of it was on a road trip to the grand canyon.... 35mpg hgw ... so I have to ask you. Do you drive like my grand father or what ?

 
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I got 40 once, but it was all highway.

 
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i get like 400miles per tank.. i use 87 octane, i put 89 and i like 350miles... it accelerates quicker though..

 
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i put 89 ..

 
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LOL! Yeah, maybe I do drive like your grandfather. I do have an auto LX, and I rarely stand on the accelerator from a light. I figure what's the point of showing people just how slow my car is. As for the highway, it's a pretty flat road, not many hills, so it doesn't drop into a lower gear much, and I was doing 120km/h with cruise control on. I filled up, and drove 382 km, and still had about 1/2 a tank left in the car.

Grandfather cruising RULES!!!!!!

 
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My recommendation is to just use the one that is recommended for your car. Just because you use higher octane doesn't mean that you will gain performance. I think Car and Driver performed a small test on octane levels using a BMW M5, Ford F150 and a Honda Accord. They dyno each car with the gas recommended by the manufacturer. Then they put higher octane gas on them drove them for a day then fill them up with the same higher octane. The results on the dyno was that the Accord didn’t gained nor lost any HP, the F150 I think gained like 3HP and the M5 lost 5HP.

 
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Octane does not have any effect in performance... Octane is a catalyst added to gass to alter the point at which it combusts under a certain pressure. So if you have a high compression motor you will want to run a higher octane or your motor will "ping" which is pre detonation. In race fuels suck as 100+ octane they use another catalyst along side octane called lead. Like the old cars.... Lead compresses very well and also make the engine run cooler. Lead make the burn cycle longer so instead of having an abrut explosion slaming the piston down the lead burns longer pushing the the piston down lfo rmore time. With a longer burn time more Horse power is created.

So the moral is if you are runnign a K20 at 11.5 compression you better be runnign at least 91 Octane unless you wish to burn holes in your pistons. I had an experince while racing Baja 500 on a Honda XR600. The gas in mexico is like 50 octane and i didn't have anymore octane boost and it melted a hole right through thee piston... It was very very very ugly :-) You might also noice in states with high elevation they have lower Octane on pumps since the air is thinner and compresses eaiser up there.

 
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I used to work with a few Mexican mechanics who had a lot of family south of the border. They always warned me to fear two 2 things when going to Mexico - the water and the gasoline.

They actually said the gasoline in Mexico is pretty much just water, so I guess the previous sentence is redundant.