God, this is a close second the the annoyance of the oil debates. Everyone wants to re-invent the wheel.

Use what the owners manual recommends, if you have to ask, you probably shouldnt be experimenting anyways IMO.

Thats why I personally just stick to the owners manual with everything including gas and oil, even have my shift light triggered for similar speeds to the owners manual suggested shift points for 'normal driving'.

Ironically enough **gasp***, my engine didnt blow up!! Funny how that works...

Don't you know every common person can improve upon multi-billion dollar Mazda's research?

difference between premium and regular is what? 25 cents a gallon? that adds up to maybe $3 at every fill up.

you decide if the difference in price is worth whatever you are trying to achieve.

I use 87 since 04 when the car was new. Never pings runs fine. I live in a cold winter climate also.

i use LEADED or a custom mixed race fuel consisting of strictly moonshine and horse piss.

have you tried comparing your average gas mileage you would get with your current 87 than with 91??

Here's the link to the previous discussion:

https://www.rx8club.com/rx-8-discussion-3/premium-regular-search-not-helping-111782/

In short, my own 2 cents worth - I've experimented extensively with various octanes (87, 89, 91, 93) over about 30,000 miles with two RX8's I've owned (2004 that I put 21,000 miles on, and my current 2007 with about 10,000), and I can tell absolutely no difference in performance or starting, in any season. I have noticed a direct inverse correlation between octane and gas mileage - I consistently get 1.5 - 2.0 mpg more with regular 87 octane, which I've observed over a couple dozen times through full tanks.

The physics of this makes sense as well. As others have said, regular gas actually has more "energy" than premium (more carbon-carbon chemical bonds to break in the combustion process, and therefore more power to be released in burning a given quantity of fuel). The higher octane premium fuels are for high compression engines, with the extra octane used to prevent detonation and pre-ignition, which thus lets the engine run more advanced spark timing and therefore get more power output.

But, the rotary engine is inherently not a particularly high compression, or thermodynamically efficient, engine. The combusion chamber in the rotary is long and narrow, which is not thermodynamically the most efficient shape (which is why our cars use more fuel and get lower gas mileage than comparable power output reciprocating piston engines). Unless a rotary engine is modified with forced induction or otherwise has its compression ratio increased, it inherently should run fine on regular fuel. Rotary engines are used in some third world countries specifically for that reason, because they are less sensitive to octane, and can run fine on the lower grade fuels often available there.

Premium high octane fuel will minimize any risk of pinging or detonation (and this is probably why Mazda recommends it, lawyers playing it safe), but these are likely not high risks in a rotary (and engine timing will automatically adjust to prevent it anyway). So, for me regular gas works fine (I refuse to be sucked in by the oil company advertising of premium fuel being the "good stuff", and don't want to unnecessarily contribute to the Exxon-Mobil corporate executive retirement fund any more than I have to...).

In short, unless you have a Honda S2000 (which I do, and it definitely needs premium), a Porsche, or some other high-compression or forced-induction engine, all that "premium is the good stuff" is just marketing hype for most cars, and a way for the oil companies to make more money.

that is simply not true.

as for timing- if the pcm adjusts the timing to ward off knock then your power is reduced and you should use a higher octane.

personal anecdote- around here I can generally get away with 89. I have never found an 87 , summer or winter, that my car will run well on. occasionally i will get some knock on 89s here and will switch to 91 for awhile. i havent found it to be brand specific either.

This is supposed to be true, but the incipient knock sensitivity of the OE knock sensor is completely unacceptable for this purpose and the RX-8's ignition timing is, in this manner, essentially static.

Ah, but it is (though not the primary reason for the reduced energy output of high-octane fuel).
What do you think they add to gas to make it have a higher AKI? Does that material possess mass?
If you answer "yes", then you realize that the energy-producing fraction of gasoline is being displaced by this additive.
Gasoline is a brew of materials with different stoichiometric values and autoignition points.

The way an engine compensates for you using a lower octane rated fuel is by dumping more fuel into the engine. (this may or may not be why some people are flooding engines I don't know if its been researched.) So if you use the proper octane rating you should actually see better fuel mileage not by a drastic number, but it will show because the engine isn’t pouring in extra fuel to compensate. The higher rated fuels do not burn cleaner, and they do not hold more energy. The way more energy is created is by compression. The higher octane rating actually correlates to a more stable fuel. You are basically preventing premature detonation in the engine by running 91 octane. The engine creates more energy because its compressing the fuel at 12:1 instead of 10:1 and so forth. The way this creates more energy is because your compressing the fuel another 20% or so depending on the engine. It’s the same concept necking down a rifle round. You have the same amount of stored energy in a smaller casing therefore creating more force on the bullet as the gas builds up from burning the gun powder.

If you want to read up on this properly you need to study the Energy Activation chemistry information.

This is actually similar to diesel fuels. You have straight diesel, then JP5 and JP8. All of which are the same base product but JP8 is meant for an engine closer to 20:1 or even 25:1 compression where base diesel is all you need in say your 1.8TDI that runs at 16:1. The ratings are just a way to show the stability of fuel under compression for the Energy Activation principle.

i had a bit about the OE knock sensor in a previous post and edited it out. just too much to get into in one thread especially since its this thread AGAIN



but depending on the blends time of year etc you can have a brand x 89 that has inherently more energy producing mass than an 87 blend from brand y.

and of course the knock resistance MAY allow you to advance the timing to make much more power on the higher octane gasoline than the lower octane.

and of course once you get into blends with alcohol or pure alcohol you can get make even more power out of the higher octane fuel because of the resistance to knock.

but within gasoline blends you simply cant say that lower octanes or higher octanes hold more energy. you also cant say that an OE tuned car (in general although ford is doing interesting stuff with its knock strategy) will make more power or be more efficient with a higher octane.

what can be said is that if an owner uses an octane that is too low for the vehicle/conditions then it will knock , which will be detected by the car's pcm which will adapt to get rid of the knock. That will cause a degradation in performance.

Use the octane that is high enough to keep your car from knocking- anything else on oe tuning is a waste of money.

This is how I feel.

I am unaware of any OEM engine management strategy that employs this.
The RX-8 certainly does not.
It is a countermeasure that can be set in place by a calibrator in the initial tuning of a vehicle, but it is not an active strategy.