The higher octane allows the engine to run at higher power per unit of fuel which is why the higher octane get more MPG than the the lower octane in an engine designed to use high octane.
High[more] octane = higher power and better[more] MPG.

Not really. Higher octane is pointless for a lot of engines. Higher octane fuel helps reduce detonation in high compression engines, and allows more advanced ignition timing. In our engine if you use anything less than 91, you run the risk of engine knock, and significant premature wear.

Edit Add: the increase in MPG is marginal, and nowhere near the cost of the higher octane fuel.

Again, higher octane rated gas does not contain more octane than lower rated gas. The higher number signifies its ability to resist premature ignition, aka knock. It has nothing to do with the amount of octane in the gasoline.

It's all about the compression ratio. Octane booster for example doesn't add octane, it increases the RATING of octane by raising the point at which it ignites, that's all. How much can I compress this gasoline before it ignites? 87? 89? 91? 93? Boom! No extra octane.

Just use wiki if you still don't know, or any of the various websites that will tell you the same.

You're not reading this post properly and you have missed the other posts that confirm using the correct high octane fuel for the engine does indeed pay for itself.

"the higher octane get more MPG than the the lower octane in an engine designed to use high octane."

Not with direct injection.
The Mazda CX-5 2L engine uses 91 octane in Oz, the lowest we have but is 13:1 the same as many diesel engines these days.

It's tuned to run on low octane unlike the GT 86 which is tuned to run on 98 octane with a slightly lower compression ratio. Both have direct injection.

And how exactly does that conflict with anything I have typed? I didn't say there is a minimum or maximum compression ratio required for each octane rating. No one said or implied that ever.

One more try: the octane rating refers to the point at which the gasoline ignites, or more specifically, its ability to resist early detonation. Nothing you say will change the science behind that, unless physics operate differently in your world...besides your toilets.

Instead of continuously arguing, why don't you just google the phrase "octane rating". Everything I have typed will be revealed to you since you don't want to hear it from me. Is it so wrong to try to learn something that differed from your previously accepted knowledge?

I don't understand why you need to make a point about octane rating as if some people might imagine it's an extra amount that's been added to increase power rather than simply being the rating given to signify the ability of the fuel to resist self igniting along with a slower burn rate.

My point is that using a lower octane fuel than the design/tune requires, loses power, raises fuel consumption and could cause engine damage.
Using a high octane fuel in an engine requiring low octane will not increase power unless that capability is built in and could burn the valves as the low flame travel rate continues past the exhaust valves.

No need to get your knickers in a twist about who knows the most.

Interesting that the direct injection Mazda engine uses our lowest 91 octane with 13:1
Does it inject just before the plug fires so that the fuel is ignited before it can be detonated?
If that's the case then why would the 86 require 98 octane or is that because it also has the port injection?

its because of the way mazda has designed its combustion chamber, it also uses multi-port direct injection to address higher combustion temps that result in detonation, vs from lean high compression single port direct injection that the FRS has. Because of this, the octane rating strain is loosened up, and can run higher CR, lower gas ratings, and not have to pull too much timing to compensate.

Thats why Mazda was able to test gasoline engines upwards of 16:1CR on pump gas, and still make very little NoX and emissions, although temps were reaching its limit.

From what im told, the SKY-R Rotary will use multi-port direct injection to boost fuel economy and emissions nearly 45% and raise performance upwards of 25%.

DI is the way to go for many makers, but so far Mazda's technology is ultimately winning in IRL numbers. Even if the Skyactive Branding is a silly marketing ploy.

this is correct! this engine is designed to burn high octane fuel,which in point of fact,(with the exception of cleaner burning),offers virtually "zero" benefit!
as you "must" burn this fuel,to get the performance designed into the engine.
so,to be blunt,we "pay" more to fuel the "beast",with no additional benefit!
it's sorta like being f**ked,WITHOUT being kissed first!,if you will!

again,correct! no additional benefit,just empties your pocket faster,is all!
may i suggest buying "stock" in the major oil companies?

....welll.....benefits can be slightly argued..

i consider cleaning burning emissions, as a result of engine seeing less knock, and less frequent ECU adjustments, allowing me to see better power at any given RPM, a benefit from using 93 octane. Just as i would with 100 octane.

while the benefit-per-dollar might not be ideal, its still a benefit.

perhaps,but know that the engine "has" to run on 93 octane,so it shouldn't be
knocking at all if you are burning the correct fuel,ie: 93 octane,and your (e.c.u.)
should NOT be making any adjustments either!..i am NOT an engineer,and i would defer to them,but this makes total sense to me! just burn the right gas,and as the aussies say,
"no worries!" mate!

Now i'm totally confused.
I thought the 13:1 Mazda had just direct injection while the 86 has both direct injection and port injection?

http://www.mazda.com/mazdaspirit/env/engine/disi.html

What is multi port direct injection? Surely it's one or the other?

Im currently running 91, but i'll be switching to 94 soon. I'm a cheap SoB.. I expense all my gas, and at the moment my work cc doesn't work at stations that offer 94... lol. Free 91 > Paying for 94. I'm sorry FR-S :(

The FRS uses 1direct injector and 1 port injector per cylinder, the direct injector has a specific spray pattern.

On the other hand, mazda skyactive uses 1 direct injector to feed 6 ports of fuel per cylinder. They claim its not a spray pattern, more like small multi-spray tubes.

http://i.ytimg.com/vi/fDFgiLrEX1o/0.jpg
http://pictures.dealer.com/b/brownsf...88ca975978.png
http://www.cleanmpg.com/photos/data/...Comp_Ratio.jpg