I filled my just under half full tank (filled with regular 87 octane) with 89 octane, 36 litres to be exact. The first time I did a similar mix-fill I felt it but wasn't sure but this time I was more aware and could definitely tell that the car was noticeably more powerful overall when pressing on the gas. Anyone else experience similar?

You might want to read this msg thread about higher octane gas making a difference. It got fairly heated about whether it does or doesn't.

http://www.greenhybrid.com/discuss/w...ghlight=octane

Link to My Hybrid Car News Web Page

I don't know about better fuel economy but there is definitely a noticeable (not big by any means but it's there) boost in power. Since I'm mixing approx. 50-50% 87 and 89 octane, does that make it 88 octane? If you don't believe me try it. It's not like you're going to premium (91 octane).

Here's what Petro Canada website has to say on the higher octane issue:

What octane does my vehicle need?
To determine your vehicle's octane requirement, look at the manufacturer's recommendation in your owner's manual. Most auto manufacturers recommend 87 octane gasoline, as measured by the (R + M) / 2 method on a test engine under defined operating conditions. If the vehicle knocks on the recommended grade, a higher octane grade should be selected. Some foreign vehicle manuals recommend a Research Octane Number (RON) instead of the more common octane rating that appears on most gasoline pumps. As a rule of thumb, the recommended octane rating can be determined by subtracting four (4) from the recommended RON number. A vehicle that calls for "91 RON" should use 87 octane gasoline (as measured by the (R + M) / 2 method). Using a higher grade than is required will not usually increase performance. However, if the vehicle is equipped with knock sensors, as many late model vehicles are, a higher octane grade may enhance performance.

Why does my vehicle require a higher octane gasoline than is recommended in my owner's manual?
There are two reasons. First, the engine may be at the upper end of the octane requirement range for the particular model. It may, therefore, knock during periods of heavy engine load. The octane requirement for each engine in vehicles of the same make is different because of variations in manufacturing tolerances. Industry testing has shown that this difference can range between two and five octane numbers. While you will not hear knock, the spark timing will be retarded, resulting in loss of power and performance.

The second reason for using a higher-octane gasoline than recommended is because the equilibrium level of combustion chamber deposits is higher than average resulting in a higher than average octane requirement for the engine. Industry testing shows that the octane requirement increase (over the initial 20-50,000 kilometres) can be as much as nine octane numbers. This means that a vehicle that was originally designed for 82 octane fuel may eventually require 91 octane fuel to perform satisfactorily.

Petro-Canada's premium gasoline, SuperClean*, contains a higher level of Tactrol*, our exclusive deposit control additive, than our other grades and will help clean up deposits left by lesser gasoline brands.

The extraordinary ability of one's mind to perceive the expected in the face of the opposite is quite unbelievable, yet quite real. It is way too easy to be mistaken about small differences in power measured subjectively (how it feels). The only way one should be confident that a perception of small differences in horsepower as a function of octane is tied more to reality than to expectation would be to be completely ignorant of which octane the car had when doing the test (say, by let someone else fill it for you, but not tell you which fuel was used, randomly switching between tanks).

On the other hand, if you have objective measurements of the performance (for example, controlled 0-60 times that are repeatable (and controlled for weather, SOC, etc.), then you would not need to be blind to the kind of gas being tested to reasonably conclude there is or is not a performance difference.

-- Alan

Alan,
Going into detail re. the difference between subjectivity and objectivity makes you look very smart. However, there are things in life that, despite all the empirical evidence, just seem to do what it is not suppose to. If you don't believe me, try it, and if there doesn't seem to be any difference you can go back to your "faithless" existence. I'm just reporting what I (subjectively felt).
Steve

I agree faith is often a factor when interpreting results. I have always found that my car performance is much better after it has been washed and polished. I believe this is due to a lower drag coefficient.

You must be the witty one in the family.

I'm sorry leepark, but I completely agree with what alan_in_tempe said. Just like me, I'm sure that you, too, have often found that what you got was not what you expected. We tend to forget such contrary events quickly, while remembering mainly those that did reinforce our expectations. Faith has nothing to do with it. This is not a religious matter! Based on my own experience, and that of many others, I'm not willing to act on someone else's beliefs, but I can be convinced by his data. Since you are making the claim, the onus is on you to provide the evidence. Someone else should not be called upon to try to disprove your assertion — it should be up to you to try to prove it.

Stan

I go along with the subjective results matching expectations camp, but it could be true. How about if someone (not me, I'm not messing with my mpg) did some objective tests with 87, 89, 91, etc. Do 0 - 60, 1/4 mile (if you have the facilities), 45 - 65, etc.

On the other hand if octane affected performance I would think that car mags (Motor Trend, Car & Driver) would do acceleration tests using different grades of gasoline and report on those differences too. The fact they don't may say something.