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.

Originally posted by Squidward
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.

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

Originally posted by ang
I can never find 91.

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.

Originally posted by ZOOMx2
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

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.

Originally posted by pepe
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

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.

Originally posted by Squidward

see my big mileage log.

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

Originally posted by MEGAREDS
... the gas here is up to 10% ethynol which, as I understand it, is nothing more than the farm lobby flexing its muscle.

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?

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

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/gasoline/gasoline_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.

Originally posted by FirstSpin
It's estimated that $1.04 per gallon in gasoline cost goes into making a single gallon of ethanol.

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 ;)

Originally posted by FirstSpin
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/gasoline/gasoline_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. :)

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.

word

Originally posted by Ole Spiff
I'm comfortable using regular since the manual says it's safe to do so.

I thought the manual calls for Premium? It says on the gas cap cover on my car at least.

Originally posted by matt
I thought the manual calls for Premium?
---
Here it is from page 4-2 of the manual:

"Your Mazda will perform best with fuel listed in the table.

{ Fuel : Octane Rating * (Anti-knock index) }
{ Premium unleaded fuel : 91 [ (R+M)/2 method] or above (96 RON or above) }"

{} above is in the table and the following is right below the 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."
---

rx8cited

Originally posted by rx8cited
---
Here it is from page 4-2 of the manual:

"Your Mazda will perform best with fuel listed in the table.

{ Fuel : Octane Rating * (Anti-knock index) }
{ Premium unleaded fuel : 91 [ (R+M)/2 method] or above (96 RON or above) }"

{} above is in the table and the following is right below the 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."
---

rx8cited


I HAVE 2 QUESTIONS... EXPLAIN WHAT "RON" IS WHEN IT COMES TO THE OCTANE ISSUE.... AND IF IT SAYS TO USE PREMIUM FUEL 91 [ (R+M)/2 method] or above...... THIS MEANS 93 IS PERFECTLY SAFE... CORRECT? WHAT ABOUT THE FLOODING ISSUE AND HIGH OCTANE FUEL, IS THERE TRUTH IN THAT?

-ERIK

RON would the "R" in the "(R+M)/2" equation; the Research Octane Number". It's the "fantasy-land" octane number obtained in a lab under low-speed conditions. The "M" in the equation is the MON, the Motor Octane Number which is obtained under higher demand conditions and therefore a lower number. And since 93 is less apt to knock than 91, yes 93 is "safe" as compared to 91 Average Knock Indicator (AKI).

Regarding flooding, you'd need a response from someone a lot more engine-savey than I to know for sure but, having worked as a chemist for almost 30 years, I can take an educated guess. My guess is that there's probably not enough difference in the vapor pressure or the flash point of 87 vs 93 octane gasoline to require different carburation for one vs. the other. I suspect that engines would flood or not-flood indepedent of the octane rating of the gasoline being used for fuel. You could stretch and say that perhaps they'd be a bit more fuel-rich because the computer controls are compensating for the lower octane and thus a bit more apt to flood, but since flooding happens on cold-starts, you'd assume the computer would be choking the hell out of the fuel-mix anyway, independent of octane.

Answer is, I don't know the answer on the flooding question, but I doubt that 87 octane would be the underlying cause.

Having said that, I want to go on record that I wouldn't put anything less than 91 in my 8. There is no 91 here in Texas, so I run 93. If I drive 1500 miles per month (which is close to my average) and the 93 costs $0.20 more than the 87 octane, and I assume 15 mpg (and that's low based on what I've seen so far), then that's 100 gallons of fuel at $0.20 per gallon; or $20 per month to protect the engine and to ensure that the I'm doing what I can do to allow the engine to run as designed. I spend $20 a month on soda pop from the machine at work. Not a huge sum, even over the life of the car.

I like the statement above that says "use what you're comfortable with." If you like 87 and like that $20 a month, it's not hurting me any. I just like knowing I'm doing what I can to give my 8 every chance to be a reliable, long-life, dependable machine.....

Another point to remember is gas prices are not the same everywhere. Texas has quite a bit lower prices than here in California. We get gouged all the time here and especially during a holiday when they know everybody is going to drive more, they'll up the price of gas 10-20 cents a gallon practically overnight.

Last time my wife was in Texas she said gas prices there were almost 50 cents cheaper per gallon than here. Southern California is a commuter community so we spend a lot of time on the road here.

All that notwithstanding I didn't switch to regular until after running some tests to see if it mattered enough to switch. It wasn't just money savings; my car actually performed better than with premium. It is more responsive, smoother to drive, easier to start in first gear and idles smoother. The dollar savings is just a bonus; I have the money to afford premium.

BTW...I love this car. It is such a great feeling to be in it and driving it. I've had it since July and the thrill still hasn't worn off. :D

You're right. We have probably some of the cheapest gasoline around. I'm paying about $1.55 for the 93 octane, sometimes a few cents less. 87 octane would go for about $1.35 or so. At first glance, I'd have explained the lower rates here on state taxes but the rate is $.20 per gallon in Texas vs. $0.18 per gallon in California. Must be in part what the market will bear. We're close to refineries here in Houston, so there's less spent on hauling the stuff but you can haul a tanker load of gasoline cross-country for less than $0.25 per gallon (probably a lot less) and some gasoline is actually pipelined. I'd assume they must move some by rail as well, which is even cheaper.

Regarding a car-commuter-society, Houston's probably on a par with LA. Before you go defending Los Angeles record, I don't mean as many cars or as many miles of road or as long traffic-jams. I mean that darn near nobody here would take a bus on a bet. There are no trains and there's probably one taxi for every 2,000 people, if that. We go everywhere by car. Add to that the fact that Houston's about 60 by 60 miles square and there's a lot of cars on the road (and at the pump.)

I'm glad the regular gasoline is working for you. Like it's been said before, "if it works, don't fix it."

The gasoline in California is at the price it is for various reasons.

Our minimum wage here is substantiually higher than that of the Federal minimum wage, which means we get to deal with more inflation with day to day expenses.

Next off, we have THE stricted emissions regulations set forth by our state government. It is so damn strict, that car dealerships are only allowed to trade cars with California State Dealerships, unlike places like Jersey that can trade with Michigan, hell, Florida if they wanted to send drivers that far. Our gasoline here is "specially formulated" to comply with our emissions regulations. Remember the oil refinery issues back in 99? That was when a pipe broke in San Francisco or some place in the Bay Area. Over night, gasoline prices flew up significantly in California. There were plenty of neighboring states that had plenty of oil, and they were willing to sell us some at a substansually lower price than that of even our regular costs, but due to emissions regulations, we were stuck bent over our bonnets without vasoline.

Another factor...we have too many well off people in this State. Too many people with Mercedez, BMW's, Lexus's and other cars that require Premium fuels. So from each bit of raw fuels, they can only produce so many different oil variants. With that in mind, they took a step down from our former 92 octane and serve 91 octane now.

For more than you'd ever want to know about California gasoline and cost-drivers in the Southern California market, I'd suggest the following reference...

http://www.eia.doe.gov/pub/oil_gas/petroleum/feature_articles/2003/cagasoline/cagasoline.pdf

It does a very good job of backing out the fixed costs (such as cost of crude) and assigning the higher-than-national-average costs, in large part, to the fact that California is phasing out MTBE and moving to ethanol as the oxygen-source in their fuel -- this transition is complicated by the fact that these two types of gasoline cannot be mixed. If I own a station and I've switched my storage tanks to ethanol-treated gasoline, it doesn't matter how much excess MBTE gasoline is out there, I'm forced to buy the ethanol-blended stocks (since the two fuels cannot be mixed). Add to that the fact that ethanol does raise the vapor pressure of gasoline and that, to offset said rise in vapor pressure, California "summer-blend" which they start making in February, has the lighter components such as butane stripped out (so as the drop the vapor pressure back down to where it would have been if no ethanol had been added) and you've got an added cost. Given that these "light ends" make up about 5 to 10% of the volume of refined petroleum (gasoline feedstock) the net effect of leaving them out of the gasoline is that you've encountered a 5 to 10 percent drop in refining capacity.

Take into account that MBTE was added at a rate of 10 to 11 percent vs. ethanol that is added at a rate of closer to 5 percent and you've lost another five or six percent in refinery-delivery-capacity. The report in the link above states that the net effect of these cost drivers was enough to cause California gasoline to rise $0.625 per gallon between December 9, 2002 and March 17, 2003. The national average rise during the same time period was $0.368 per gallon.

Interesting, if somewhat tedious reading.....

Once again...anal rapage. And they are not even courteous enough to provide some vasoline or give the reach around.