WHICH OCTANE IS BEST?
 

Considering the flash point of certain octanes and how it may affect the "flooding" issue that I don't understand completely yet... Which octane is best for the engine, that is high enough to prevent knock but low enough to avoid flooding? Or am I totally off the page?? lol

P.S. Want to thank everyone on this site, I've learned sooooo much!....Erik

i've used both supreme and regular unleaded octanes extensively (see my log), and have come to the conclusion that supreme is a waste of money.

see my big mileage log.

Thanks Squid... Your log is very helpful, I see you used 87 a lot. Have you or anyone else reading this post had any spark knock problems running 87? Or is that not an issue with this vehicle? I recall reading a post from another gentlemen who said he got some serious spark knock when he put it to the floor on the freeway running 87 octane? -Erik

here in the land of Oz, we're told to use a min of 95 octane... most of us use 98 octane... that's also to do with the quality of our fuels here, the 98 octane stuff is much cleaner

Oh, and don't know anyone who's flooded one yet ;)

I am a big fan of 87. Never a problem, 1700 miles, and I like to set it through the paces. This car is so much more than Im used to, my butt dyno is more impressed by the $.20/gal cheaper gas.

I can never find 91.

The problem of using a lower octane rated fuel on a high compression engine (9 or higher) is engine knocking. You may not hear it but it's occuring. Recommend fuel is the best course.

Higher octane only effective on high compression engines. it has NOTHING to do with mpg.

And really, .20 for 15 gallons is only an additional $3.00

Follow the Engineers, not the butt dyno.

Higher Octane does not effect milage. It helps high compression engines from knocking.

91 is reserved for us poor "assed out" bastards over here in California.

In all honesty...91 is the recommended octane. One has to considers that the engineers took into account he car can probably get away with 87 octane, but if numerous factors were to occur, then the 87 octane wouldn't offer enough of a buffer to compensate for the issues at hand. What are the issues that I'm talking about? Well...what if one was to get a crappy tank of 87 octane? On top of that, it was a nice hot 100 degree day. Also...you need to climb up a nice, steep, steep hill. Well...even a decent tank of 87 might give up on you.

I was skeptical when I first read that thread. However, after hearing my 8 knock a few times I have quit using 87 octane.:o
I have not heard Knock while using 89 or 92 octane.

Isn't ozzie octane measure differently than US? Meaning your 98 might equate to 93 or 91 here? They don't even sell 98 in the states, and in calfornia 91 is the highest we can get.

Concur with the many rationale comments here that octane doesn't affect mileage, only compression (with slight loss in perfornance.) If you search some very old threads you will see how emotional and contentious this issue was when the cars just arrived here. I was basically the sole proponent of using 87, and the entire forum ganged up on me and said I had no right to own an '8.

7800 miles later and still 87 with no knocks. First time it knocks, i'll go to 89 but doesn't look necessary yet. glad to see others are making their own choices on this now.

Geez. I think I'm using 94. I'm not sure but think in northern Illinois we have 87, 91 and 94. I also know that the gas here is up to 10% ethynol which, as I understand it, is nothing more than the farm lobby flexing its muscle.

Squidward, your log shows 38 mpg on Nov. 10. Call Mazda... they'll want to interview you. ;)

Real good point, megareds. Anyone knowledge here (like petrochemists) to talk about this? What does adding corn oil or whatever it is do to our mileage, compression, and performance? I agree this scam is politicians kowtowing for campaign donations from wealthy farmers, and the payback is from all of us at the gas pump going back into the farmers pockets. Lovely system; in other words, politics as usual and the small guy gets screwed. But what does this ethynol due to performance of our cars?

Haha I didn't even notice that.. I just recently added the last 15 entries. I guess I did it so quickly, I paid little attention to the figures. Good catch.

Checking the original receipt, I remember now. I was in a hurry to a meeting that morning, so I pumped only 5 gallons.

I'll update the log to correct the descrepancy.. I'll remove that entry and combine the fuel pumped, mileage, and cost into the next entry. That should correct it.

Here's a good source (overview actually) for the basics in octane; what it means, how it's derived, what influences it, how it impacts engine performance, the consequences of running lower octane in high-compression engines, octane boosters, and good stuf like that......

http://www.omegamotors.com/enjoy/gas...soline_06.html

Regarding ethanol added to gasoline, it burns more cleanly but has only about half the btu's per unit volume in combustion power potential. Gasoline averages about 115,000 btu per gallon. Pure ethanol averages about 76,000 btu per gallon.

Add to that, the farm-equipment-gasoline per acre burned in planting, cultivating, harvesting and re-conditioning the soil in the process of raising corn and the energy costs of transportation of the feedstock, the energy costs of fermentation and distillation, followed by more transportation costs to take the ethanol to a refinery (for blending) and you're better off just buying gasoline in the first place. It's estimated that $1.04 per gallon in gasoline cost goes into making a single gallon of ethanol. (Cornell University studay easily found with Google.) You're right, it's a ploy to keep the corn-farmers happy.

The obvious conclusion is that Americans should drink more ethanol-based beverages. This would sustain the cost of corn and we could have the proper level of btu's in our tank. :)

Actually I'm using 90 octain but that was not a voting option so I checked 89. Using 90 octain I've been getting 18 - 20 mpg even in the cold temperatures here in Minnesota. I now have put on 5000 miles and it seems to be getting better mpg as time goes on.

That's an astonishing, but very believable, story. Just another case of politics gone bad. Anyone from a farm state care to defend ethanol?

It's believable. The United States government pays, and has been paying corn farmers in the mid-west to NOT grow corn in their fields. I learned that from American Government ;)

A very true, but sad statement about our farm subsidies. Isn't it great that Iowa is the first state in determing the presidential nominee for each party? :mad:

My grandfather's best "crop" was un-corn. He was a farmer in Arkansas and got paid by the government not to grow corn. He let the land out to a cotton farmer and collected "rent" on the same land he wasn't growing corn on. Made a pretty good living between that, some loan-sharking to the locals, and his social security check.

Damn...wish I had a means of that sort to make some money. Your grand pappy buy many toys Spin?

Well, for my opinion...I use the 91 or better octane rated fuels. My reasoning? I just shelled out $31K for my beautiful and amazing RX 8 and like it is stated above an extra .20 per gallon is worth it to keep my baby in good health as long as possible! It may not knock now but what's to say saving $6 a month will be worth rebuilding an engine in 5 years rather than 7 (numbers used for correlation only and not intended to be actual facts or suggested thruths) ;) Again if you have to ask why, then wait a minute and ask why NOT?

Been using 87 octane for months and it's working great. As for the paranoid, use what you're comfortable with. I'm comfortable using regular since the manual says it's safe to do so. The computer reads what's going on inside the engine and makes the necessary adjustments to prevent knocking. I have confidence in Mazda engineering. I use regular gas and I'm not worried in the least.