This may be a stupid guestion but here goes,To get the best performance I should be running the highest octane I can get right?I was reading a thread on another forum about some of them saying you are just wasting your money.I dont know alot about the wankle and this is just another thing I guess.. :o
btw I run 93 here in Indiana..
Shark

higher octane is better performance.

ok. i've been using 93 since i bought the car and the last time i filled up, i put in 89 just to see if the car would perform differently. so far, no major differences. i can feel "less smooth" in higher revs than compared to the 93 but nothing bad. i'm also getting much better mpg. i may do it again for another tank to get the full effect, but so far i'm not convinced either way.

I'm also running on 89, but I really don't know how smart that is. The rotary engine can be so temperamental and sensitive, you have to be careful. For a few months, I dropped to 87 and it caused really bad engine knocking when I revved the engine high. It also felt a little more sluggish. So far with 89, I'm not having as bad a problem, although I do get the infrequent knock (dealer mechanic, and others here, say it has to do with the fact that the change in octane causes either misfire or screws up the engine timing--I can't remember which). Having used all 3 grades here in GA--87, 89 and 93, I do not notice a change in gas mileage.

Higher octane resists engine knock better. The RX-8, like many cars nowadays, has "knock sensors". If they sense that knocking is imminent the computer does things like retard ignition timing, to prevent damage to the engine. These anti-knock measure also reduce power. So, it is possible that 93 octane may give you some additional power under conditions such as maximum acceleration where knock is most likely. But, it is not a guarantee of additional power. There are many factors that come into play. Even the manual only mentions a "slight" reduction in power. Whether or not that's important or even noticeable is up to you.

Also, octane rating does not necessarily correlate with the energy content of gasoline. In fact it is possible to increase the octane rating by adding compounds that actually reduce the "energy density" of the fuel. So it is entirely possible that you are getting better mileage with the lower octane. Again, many factors and it depends on how the particular gasolines are being formulated.

Personally I've always followed the school of thought that says don't buy more octane than you need. The manual says I can run 87, and my car seems to have no problems with it so that's what I use. Other peoples' circumstances are different. Such things as altitude can influence octane requirements. Also, how you drive. I think you're taking the right approach by trying different grades. If running a lower grade works for you, go for it.

The octane rating is also a reference to the ignitability or stability of the gas-i.e 93 octane is more stable and burns slower-allowing the engine to run more timing=more power because the flame front and rotor interface are able to make contact at the optimum angle or stroke if we were talking pistions. Under such situations, a lesser grade can ignite prematurely or too quickly, causing detonation or pre-ignition.

Wow, very interesting info that I never knew. Thanks for the insight, Nubo and ma5.

I guess Ill try a few tanks of 87 and see what happens.Thanks for the info peeps.
shark

Just keep in mind that you won't necessarily hear or feel every single ping or knock if you use lower octane gas...and by the time you do hear it, you may have already done serious damage to the engine. The rotary in particular is sensitive to knocking due to the apex seals.

Stick with 93. However, I have heard from reliable sources that a lower octane is better during cold, cold months. Can anybody else confirm this?

- Irish
P.S. I actually read a thread once where someone put 110 octane in their 8!! Nice!

Good info, I better boost upto 93.

I've used all three grades and haven't noticed any difference in mileage and/or performance. I usually stick w/ 89 mid-grade though.

i've been using 89 octane for a year and a half now without problems (even with a cz unit)... i get better gas milage with 89 octane and with all the data logging i did i never saw the car act differently that would give more performance with 93 octane when i tried it

I'll let y'all know when I get a new engine :D. So far 16 k miles on 87 octane and it's not damaged yet.

Higher octane does not necessarily mean better performance.

Higher octane means better protection. The higher the octane fuel, the less likely it is to ignite out of phase (or detonate). The more you compress a volatile substance like gas, the higher the temp and the more likely it will, literally, blow up under pressure.

With that in mind, 87 octane SHOULD be the most efficient form of fuel since it is easy to ignite... giving you total burn and full power. But, it may ignite all by itself (sans the aid of a spark plug) and cause trouble in that brittle engine. The manual recommends 91 octane or higher because the compression ratio of our beloved 8 is ~10:1. That is...fairly... high and may cause some detonation on 87 fuel.

23000 miles, 99% on 87 octane. Did two tanks of 93 a while back when gas prices dipped. Maybe a little smoother and about a mile/gallon better mileage, but at $.20 /gal price difference it doesn't seem worth it. I'm averaging about 19mpg in mixed driving.

Mreilly, which brand of gasoline you use in NJ? My car was pinging on Shell 87 but is OK with 89.

Mainly, Citgo. Sometimes Sunoco or Shell.

As a point of argument - the manual does not warn against 87 octane on the basis of engine damage, rather it cites performance. It only cites concern for engine damage with fuels BELOW 87 octane.

Correct me if I'm wrong, but doesn't the manual recommend 91? Why can't I find 91 anywhere? It's either 93 or 89.

Octane rating is determined by many factors.

91 is the minimum because in places like colorado (mountains), 93 octane is not available because of the air. Octane is rated by the amount of fuel that can be compressed before it blows up. In thinner air (mountains), it is easier to compress the fuel. Hence, in colorado and other such places, their highest octane rating is 91.

Correct me if I'm wrong, but doesn't the manual recommend 91? Why can't I find 91 anywhere? It's either 93 or 89.

Because you are very lucky. Out here in Cali. the best you can get is 91 octane. I wold love 93 octane, that would allow those of us with turbos to run a little more boost and not have to worry as much about detonation. If you use 93 octane it is fine for the engine. The engine is set to function optimally at a 91 octane. If you put 93 octane or higher it might get you a few more hp, it might not as the engine is a it's peak performance at 91 octane & up. If you use 87 or 89 octane the car will just not function at optimal settings, i.e. it may retard timing and lower your hp. But for around town driving this might not matter to some people.

This subject has been brought up a few times, there have been a few threads on this. I linked an article that was done by Car & Driver on octane ratings & performance. On cars set to run with 87 octane gas (Mustang & Hoda Accord) there was little gain on using 91), but on cars that were recommended to run 91 octane (M3 & Saab Turbo) performance & hp dropped 6%-12% when they used 87. Please no "seat of the pants" performance comments by the peanut gallery please.

I think I will go ahead and just use 93 unless the price just breaks my bank.....

As a point of argument - the manual does not warn against 87 octane on the basis of engine damage, rather it cites performance. It only cites concern for engine damage with fuels BELOW 87 octane.

Exactly!

Better to be safe than sorry, if you can afford it........

i live in NJ and the sunoco's here have ultra-94 octane and thats the only one i'll feed my baby with.. it's only 1 more octane... but costs like 9 cents more than 93 octane... but it's worth it cuz i feel better =P

higher octane is better performance.
Since when?

Unless you are running non-stock timing or other modifications, running higher octane will not yield more performance, it will only hinder it. Until you do ignition and timing modifications or some kind of forced induction, it is best to stick with what is advised by Mazda.

I know for non-turbo earlier model rx7's you wanted to run the lowest possible octane of gas you could get.

Also remember, higher octane will cause more carbon buildup which is not a rotary's friend. Only run higher than suggested octane if you need to.


EDIT:
Since I haven't had a chance to actually look in my manual yet because I haven't even taken delivery of my rx8, what IS the recommended octane for the rx8?

...what IS the recommended octane for the rx8?

Quoted from the owner's manual:

"Your Mazda will perform best with fuel listed in the table."
Table contains:
"Premium unleaded fuel | 91 [ (R+M)/2 method] or above (96 RON or above). "

Then under table:
"You may use a regular unleaded fuel with Octane Rating from 87 to 90 (91 to 95 RON) but this will slightly reduce performance. Fuel with a rating lower than 87 octane (91 RON) could cause the emission control system to lose effectiveness. It could also cause engine knocking and serious engine damage."

I've opted for the slightly reduced performance.

Need to figure the math, if I use one tank a week, $0.20 difference in 87 vs 91, hmm, $3.00/week. Think for the performance will stick with higher grade. Hell cut out one of those starbucks coffees a week:)

Since when?

Unless you are running non-stock timing or other modifications, running higher octane will not yield more performance, it will only hinder it. Until you do ignition and timing modifications or some kind of forced induction, it is best to stick with what is advised by Mazda.

I know for non-turbo earlier model rx7's you wanted to run the lowest possible octane of gas you could get.

EDIT:
Since I haven't had a chance to actually look in my manual yet because I haven't even taken delivery of my rx8, what IS the recommended octane for the rx8?

Mazda advises 91 Octane for optimum performance. Today's high compression engines have adverse effects from low octane fuel (vs. previous generation engines). The ECU will retard (turn down) timing & remove power. Many people who have run 87 octane whether because the quality of the fuel, or the terrain they are driving on have gotten detonation. 87 is about the lowest range where the engine can still compensate by reducing timing. Any batch of bad 87 (not really 87, might be slightly below 87) and you may run into problems. Unless you are talking race gas (100 octane+) it will not really hinder performance & it won't give much increase in performance either. The car is set to run on 91 octane, if you use 92 or 94 octane it can only advance timing so much then it is functioning at the factories "optimal" level (where Mazda feels it is safe to set advance). If you get a Canzoomer unit where can can advance the timing, you may be able to advance the timing beyond "factory specs and get more hp. I have seen some people/companies run a 91 octane "street" level, and a 100 octane "race" program on their ECU's.

So the owner's manual is wrong? :rolleyes:

Since when?

Unless you are running non-stock timing or other modifications, running higher octane will not yield more performance, it will only hinder it. Until you do ignition and timing modifications or some kind of forced induction, it is best to stick with what is advised by Mazda.

I know for non-turbo earlier model rx7's you wanted to run the lowest possible octane of gas you could get.

Also remember, higher octane will cause more carbon buildup which is not a rotary's friend. Only run higher than suggested octane if you need to.


EDIT:
Since I haven't had a chance to actually look in my manual yet because I haven't even taken delivery of my rx8, what IS the recommended octane for the rx8?

So the owner's manual is wrong? :rolleyes:
Your comment was only higher octane = better performance. This is definitely not always true. I dare you to run 91 octane in your car, dyno it, empty the gas tank, run 110 octane and redyno. See what happens, you'll get lower numbers.

Now if the rx8 was meant for 91 octane, then use 91. But don't expect that if you fill up with like 110 or 115 at the dragstrip to suddenly drop your times a ton.

Sorry I don't want my car knockin, that can't help the engine.

Did you even read my full post? I said

it is best to stick with what is advised by Mazda

So if suggested is 91, 93, whatever, run it and be happy. But you will not yield more power from like 110 or 115, etc, at the drag strip on a stock car.

You were saying higher = more performance, that is wrong past what Mazda suggests. Why would higher octane just automatically make your cars performance increase when completely stock?

Now if you consider performance as fuel economy or engine wear, once again higher isn't better past what mazda suggests on a completely stock car. Higher octane, when not needed, will just cause more carbon buildup and worse fuel economy.