ooo from what i read.. our compression ratio for the octane to be used at 91... isnt really so much of a difference.. but i have used 91 for my other car (TL) but now with the newer cars you really dont need the 91 anyways since the fuel injectors are good!

 

What does it say in your owners manual? Mine says both the 1.8L and the 2.4L are designed to be used with 87 octane. Any serious reading on the subject suggests that paying the extra money for the higher octane its going to net you no benefits in terms of performance but it will cost you more. Makes a difference if the engine was built for something higher like some of the luxury/performance cars out there.

 

research octane number 91 (RON 91) equals 87 octane for most of us on this board.

we had this same discussion over at yaris world, where many began to argue the yaris was "researched" using 91 octane because the back of the manual said: fuel type: 87 octane (research octane number 91) research octane number (RON) 91 does not mean they tested our cars with 91 octane. the manual is just listing a different version (used in much of the world) of the recommended fuel type.

the chart at the bottom of this link shows a good comparison of how RON octane numbers used elsewhere equate to the PON (pump number) that we are used to seeing.

http://www.btinternet.com/~madmole/Reference/RONMONPON.html

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.
There is another type of octane rating, called Motor Octane Number (MON) or the aviation lean octane rating, which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.
In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States, Canada and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 8 to 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "regular" gasoline in the US and Canada, would be 91-92 in Europe. However most European pumps deliver 95 (RON) as "regular", equivalent to 90-91 US (R+M)/2, and even deliver 98 (RON) or 100 (RON).

 

i have used nothing but 91 octane gas in my corolla since i bought it.... there are those thats say there are benefits and those that say there are not... i spend the few extra pennies, you never know maybe it will burn slightly cleaner and give me 0.001 extra HP:naughty: , (cmon guys its what? a buck fifty extra a tank?)

 

My dealer specifically told me not to put premium fuel in my Corolla because and I quote "It wouldn't know what to do with it." So I've been using regular. I usually go to chevron with their "techron" additive so maybe I'm getting something there. But really, I'm just not willing to pay more for gas that hardly has any noticeable benefits. Just my .02

 

Higher octane is used to suppress the ignition of the flame kernel to prevent pinging and pre-detonation or having the fuel ignite before the stroke of the piston has reached its full compression. In performance cars higher cylinder temps cause pre-detonation so the increase in octane is needed and actually slows the ignition of the flame so that it will time more accurately with the compression stroke. Turbo and supercharged cars often need higher octane for this reason as well as some other higher compression engines.

In the corolla (both engine flavors) the compression is such that higher octane is simply not needed. Higher octane 91 can actually cause fuel economy to be lower than 87 octane gas because the flame doesn't have time to fully ignite thus not capturing the full energy of the combustion explosion cycle. The knock sensor in our engines adjusts for nearly all of the conditions present at our altitudes by retarding timing automatically. If one was to use 85 octane at sea level and then go up to the mountains there may be some pinging that the engine might not be able to compensate for so in that case 87 octane would be more appropriate.

 

a few years ago I tried out every different octane I could find (I think I got 86 through 93) and logged my mileage. This was in a '98 Tacoma. The lower I went, the better the mileage, no exceptions.

 

I use 87 octane the 89 octane around here has mixture of 10% ethanol and 90% gasoline. I get about 4 mpg less on average if I use gasohol. The ethanol produces less BTU's then gasoline. 87 octane is usually about 8 cents a gallon higher.

 

BP Silver rated at 89.

 

The fuel additives should be the same for 87,89,91 octane etc., so long as they come from the same station. The difference lies in the amount of branched carbons that translates to how quick or slow your gas will burn. A higher octane requires a longer burn time. This is okay for cars that have sensors that can adjust to it, and utilize the higher power gain from it (completely burn the fuel).

If the corolla does not have the ability to retard ignition timing, you guys will see carbon buildup and a decrease in performance over the life of the car.

 

The fuel additives should be the same for 87,89,91 octane etc., so long as they come from the same station. The difference lies in the amount of branched carbons that translates to how quick or slow your gas will burn. A higher octane requires a longer burn time. This is okay for cars that have sensors that can adjust to it, and utilize the higher power gain from it (completely burn the fuel).

If the corolla does not have the ability to retard ignition timing, you guys will see carbon buildup and a decrease in performance over the life of the car.

I suppose the natural inquiry would then be does the Corolla have this capacity. How would the consumer determine this?

 

I bought Corolla for it's using 87 octane.

 

Use the 87, unless you have money to throw away or it makes you feel better.

 

Actually, with a higher octane fuel, you want to advance the timing. The problem with using higher octane than the engine is designed for is mainly the waste of money. In Canada, premium gas is typically 11-12 cents per litre more.

The Corolla engine will retard the timing if it detects pinging or knocking, but I doubt it has a performance enhancing system that advances the timing to the point of detonation and then backs it off slightly.

Higher octane is not "more powerful" or "better" but just more resistant to burning. This allows very high compression engines to squeeze it more before it would self detonate (as in a diesel engine).

But, whether an engine requires, or justifies, premium gas is more complex than the compression ratio. It is also the shape of the combustion chamber, the location of the valves, the size and number of valves, the valve timing and lift, and so on. The engines "squareness" is also a factor (the bore to stroke relationship, so how far it is across the piston). So, it is possible to have an 11:1 engine that runs great on 87, and an 11:1 engine that detonates like mad on 87.

Modern engine designers don't leave much on the table today. Go with the specs for fuel.

 

Does the quality of gasoline have any impact on your analysis and engine performance? I have always used Amoco/BP and have read from many sources that it is consistently ranked among the best gasolines. Is there really a qualitative difference between the name brands and that sold by "Billy Bob's Gas House"?