Why should I run higher octane fuel?

Will it give me more power? Due to the knock sensor in the ef falcon


will it just make my motor run more efficient?

Generally higher octane fuels will provide you with better efficiency, a cleaner engine... Blah blah blah...
All I know is that I get 850km from a tank of high octane, but only get low 700's from regular fuel... Highway driving I reccommend it, city driving you don't get as much value. Though I suggest a tank every third or so in order to clean out the engine etc.

I used to always run 95 then 98 every month when it was cheap . Now i always run 98 . Been running 98 for a while now , the other day I filled up with 95 and I definitely noticed a drop in economy . Now i always run 98 just because it lasts longer , no idea whether it increases power or cleans . I do both highway and some town driving .

The octane rating is only an indication of the fuels resistance to detonation.
Nothing more nothing less.

+1 i did a basic tafe course and they went into the subject of fuel and its resistance to knock or detonation as you said, i used to run it in my ef and it made difference in power with the autotragic gear box, in the manual car not so much noticable but the economy is definatly effected in both the el (dizzy)and the ef (coil pack) cars

thanks for the reply boys, i dont know weather to just stay on unleaded or go to the higher octane, i do all around town kms

95 has a higher density (energy) than 91...98 has a higher density (energy) than 95...chemical engineer from shell told me this...

you will definately get more range out of higher octane....is it worth the extra money, maybe..

On the open road, go with 98. If you're only driving around the city, save a penny or 2 and go 91 or even 95. Yes 98 you will have more power, and it burns better, but the constant stop start in low gears is going to just chew away all the benefits of having 98. But like said before, if you run 91 normally, try put a tank of 98 in once a month just to give a clean flush of good fuel.

All other things being equal, increasing the octane going into an optimally tuned engine will produce very slightly less power. As already said, octane is a measure of detonation resistance. But higher octane fuel also burns a little more slowly, having the same power-reducing effect as reducing ignition advance. I read an article in a US magazine where they built a big-block street engine, achieving an almost perfectly flat torque curve. The tuning was optimised on the equivalent of 98 octane and put on an engine dyno. Out of curiosity, they did runs on 96 and 93 octane, and the power and torque increased each time. As the fuel was burning faster, it was creating more cylinder pressure before the exhaust valve opened releasing it. The effect is measurable on a dyno, but you would be unlikely to feel it.

The big exception is if the lower octane fuel is causing detonation, so the knock sensor is kicking in and pulling out gobs of ignition advance. Increasing the octane will stop the detonation, and you get more advance and heaps more power. So, if you have increased the compression, or have advanced the ignition, high octane can help a lot. Normally a factory ignition advance is set very conservatively, and leaves heaps of power on the table, to avoid detonation. However, if you use higher octane fuel and get your ignition tuned to take advantage of the detonation resistance, you can get that power back. That's what the chip manufacturers are doing when they sell chips tuned for different octane; the higher the octane, the higher the power.

A less common exception is if your engine is already running too much advance (past the point of maximum torque), the longer burn time of high octane will actually increase power a tiny bit.

The other factor is that high octane fuels generally have more detergents in them, so they keep your injectors, valves, and combustion chambers cleaner longer, giving you slightly higher power over time, especially if you use high octane all the time. Dirty injectors and carboned up chambers are power robbers.

I use only 98 in both my XR6s. In my AU to keep it cleaner and reduce the chance of the knock sensor being triggered. And in my EF because it has increased compression and a J3 chip with advanced timing, so it needs the higher octane to run safely (and produce the extra power that it does).

Do the premium fuels offered at the pump have a higher energy density? (lets ignore octane ratings for now)

From what I have read, there is effectively no difference in energy density (energy per litre - I believe "heating value" is the technical term) between high octane and low octane fuel. See the quote from API below. But high octane petrol is less "volatile" than low octane - it takes more heat to ignite and burns more slowly. So, difference in volatility must more than compensate for any difference in energy density that may exist.

"Gasoline with a higher heating value (energy content) provides better fuel economy. Traditionally, premium gasoline has had a slightly higher heating value than regular, and, thus, provides slightly better fuel economy, but it is difficult to detect in normal driving. There can be even larger differences in heating value between batches of gasoline from the same refinery, between summer and winter volatility classes, or between brands of gasoline from different refineries because of compositional differences. The differences are small and there is no practical way for the consumer to identify gasoline with a higher-than-average heating value."
http://www.api.org/Oil-and-Natural-Gas- ... ctane.aspx

Here's an example of how much power you can gain using higher octane fuel IF YOU TUNE THE ENGINE TO TAKE ADVANTAGE OF IT:

EF XR6 stock 164kw 91 octane (factory ultra-safe tune)
Powerchip 175kw 91 octane (optimised tune)
Powerchip Gold 178kw 95 octane
Powerchip Gold 98 183kw 98 octane

http://www.powerchipgroup.com/Datasheets/1/For0051.pdf
See page 7 especially.

that Powerchip company is absolute s**t i would not believe anything they write. sorry..

Yeah, im aware of that concept. Octane rating != Energy. My question is regarding the products that are sold at our pumps. Forgetting about the octane value - do the premium fuels have higher energy density?

Certainly if we're comparing E10 blends we're looking at lower energy density. So what about the other grades of fuel available at the pump.

API says there's no difference in energy density that you could rely on. One production batch vs another of the same octane could have more variation than between regular and premium.

Yeah, Powerchip may not be able to do what it claims, but the principle of "more octane=more ignition advance=more power" holds true and is a fundamental tuning method:
http://www.youtube.com/watch?v=gQghB4asSnI