RX8Z

I am aware there are tons of this topic, but seemingly there hasnt been a final answer to what Im looking for.

Being I work at the dealership, I was told specifically by a Mazda technician who works on the Rx-8, that the engine does not need anything higher than 87 octane fuels.

The rotary is not a piston engine , therefore would not take advantage of the higher octane. I am not an exper in fuel criteria with rotary's, so perhaps someone can get down to the technical details of this. However it is my understanding that octane ratings measure a gasoline’s ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders.

A few buddies of mine and myself have been using 87 octane. Our cars run fine and quick, however theres been some personal declarations here stating tha 91 is faster and performes more efficiently..

Is this a fact or a myth? I do know it is true that many poeple have a false belief that because running a higher octane, they think its a better performer but we all know that isnt the truth. Has anyone run any tests or an analysis on fuel performance? Just wondering..

Drive safe ..

Z

Xyntax

I have been supporting the use of 87 octane on our RX-8, but lately I have been having inconsistent results. Using 87 saved me fuel before. But when I got back to 91, it saved me more. 87 also solved the rough idling of the car, but going back to 91 made it even smoother. Power delivery was also the same. 87 felt better, but then when I got back to 91, it improved more.
I dunno, maybe it's the back and forth switching between 87 and 91 :D

MazdaManiac

iTrader: (3)

There is a ton of stuff that gets brandied about and asserted as fact about the use of high octane fuel.

You are correct on your understanding of pre-ignition and the function of octane as a resistance index to pre-ignition.

Additionally, octane works against the production of power since the same resistance to pri-ignition is resistance to combustion in general.

That said, there are a number of people that have reported increased fuel economy with lower octane fuel.
However, there is no one with numbers to suggest higher octane produced more power in thir RX-8.

The issue that is addressed by higher octane is the fact that most gasoline formulations sold in North America are suspect at best and the cushion provided by a higher octane rating is not to be dismissed.

I suggest that you read this thread that I started a while back:
https://www.rx8club.com/showthread.p...ghlight=octane
It contains a lot of information that might interest you.

rotarygod

I personally have always used the lowest octane that I could get for my RX-7's (nonturbo). The turbo uses 92 octane. Any time I have ever run high octane in a nonturbo rotary, I have only seen a difference in the weight of my wallet. Alot of the perceived gain was mental and I've never seen a difference in mileage from changing.

pp13bnos

I guess I'm out of the norm for running higher octane.

I talked about it in anouther thread. But, I'll give a breif sum of what happend. I dyno'd my 6spd Rx-8 with around 4-5 gallons of 110 oct. unleaded fuel. I put down 161rwhp. My buddy dyno'd right after me, in his 6psd, with 91 octane. He put down 154rwhp. Bolth of us had around 2,500 miles. Bolth with 6spds. My car was Red with the app. package...his was silver without. Perhaps the wing added the extra rwhp? I guess we'll never know.....

And btw, my car made peak power right at the rev limiter, and his made it around 1k rpms less than mine. CJ

wakeech

woah, those are pretty low dynos... 2 wheel only??

pp13bnos

They where on a mustang dyno. Wich is typicaly 10% lower than a dynojet. I'm taking my car to the drag strip this weekend, as long as the weather is nice anyways. That way I can get an idea of what type of power its realy putting down. CJ

MrWigggles

I would like emphasize that octane and power are not related directly. Higher octane will help curb pre-ignition but won't necessarilly make more power. There is a seperate un-published drivability index that deals with the actual performance of the gas and that is seperate thing from octane (and yes the gas refineries have to meet a required level).

If you mix Xylene with 87 octane to get to 92, you're going to be a lot faster than if you bought 92 straight which can be made out of cheap added fuel designed to raise octane rating but not driveability.

Do a search on the use of xylene and you'll get a great discussion about octane.

Personally, I am using 87 octane until it gets really hot here in Houston.

-Mr. Wigggles

wakeech

yeah, the "Octane Booster" thread i've got stickied that's the xylene thread, i'm pretty sure.

Nubo

My understanding is that in theory 87 octane could result in anti-knock sensor activation causing some retardation in timing to avoid the knock; thus lower power. How often or to what extent this would be the case is not clear but would depend on a number of variables including temperature, humidity, atmospheric pressure, engine condition, demand being placed on the engine, and gasoline formulation. As has been mentioned the available energy in gasoline doesn't necessarily correlate with octane rating and in fact you might find a higher octane fuel with less power density depending on the "tricks" used to raise its octane rating.

wakeech

nope, the anti-knock sensor is not proactive, it waits until it detects knock (which could be gravel flying up off the road and hitting your motor hard, or actual detonation itself).

jep, we got the "potential energy does not relate to octane " down in a few posts already, but it won't hurt for another two. ALCOHOL ENRICHED GASOLINE IS BAD FOR POWER :D

IKnowNot'ing

Some people here seem to get confused : knock and pre-ignition are two different things.
Knock is an abnormal combustion event that takes place after plug ignition, in the end-gas (remaining unburned gas pocket during combustion), due to a transfer of heat and the rise of pressure beyonf the flame front.
Pre-ignition is a much worse phenomenon where, after heavy knock, a hot spot os created in the combustion chamber that ignites the charge before plug ignition. It's not the sparking (hence the ECU) that controls ignition and top piston lands or rings get heavily damaged.

The main difference between two octane rated fuel is its ability to resist to knock. Theoretically, the higher octane, the closer to MBT (optimum for power) spark advance you can go.
However, in engine management systems (EMS), especially Ford ones (Mazda is owned by Ford), the Program Office select an octane rating (sometimes different by markets : NA, EU, Japan...) and map the engine to this reference fuel.
From there, there are 2 options : they decide this octane rating (say 87 US) is the minimum requirement and they let the knock control advance spark timing until knock re-appears. In this instance, running a higher grade fuel will provide some benefit although it's going to be so small the average driver won't really feel it.
If they decide to play safe and protect the engine even if a lower grade fuel is used, they will map the knock control in such a way that it will retard and work from a lower spark table when too much knock is sensed. There is very little use to go beyond the recommended fuel in this instance.

Now, Ford uses reference fuel at exact octane rating (ex : 95 RON is 95 RON). At the pump, in Europe, the 95 RON fuel actually makes 96.5 RON in average.

There is a slight difference between two octane grade fuels in H and C contents which affect density, stoichiometric AFR, and calorific values.

Trx8

This is a strongly related thread:
https://www.rx8club.com/showthread.p...threadid=20976

RX8Z

I truly believe there is no benefit to use anything higher than 87 octane on our engines.

The fact that some people state they are performing better or more fuel efficient, is prob more mental than factual.

Or could be the chance that the gas quality wasnt as good as it should be. Assuming that the 87 octane is pure and clean in the best of quality, the rx8 should run at optimal performance as it should.

Keep in mind, that whoeva stated they ran a dyno and got better results, I believe that because you ran it on a Mustang engine which is a piston engine. That makes sense to run a higher octane fuel, but a rotary is not a piston...

anyways, maybe one day.. C/D or M/T will have an article about fuel consumption and performance, maybe we should all write them a nice letter =)

btw, according to that thread posted above, they were saying that Shell gas was the best? I dont know, on the east coast.. I would believe that Mobil is the best quality gas in our areas but im sure geographically that could vary..

pp13bnos

A mustang dyno is not a car. Just like a dynojet is not a car. CJ

RX8Z

sorry, i read it fast.. i thought you said you ran on a mustang =)

but anyways, according to your analysis, you ran a higher octane, but how long prior did you have that fuel in your tank? same with the other car

If im not mistakened, the engine has to readjust itself to different octane levels.. assuming youve always use that same fuel, i can say your test is more or less accurate, however if you just dumped that fuel in prior to the dyno, that could be a major factor.

but wuteva the case, a friend of mine who works on rotary engines (professionally) stated to me that whoeva states that an NA rotor engine runs faster or performs better with higher octane is full of ****. Basically what he was saying is that , there is no difference and its all in the mind. This guy has owned 3 Rx7's and 2 rx8's currently . 1 is a project car that is he working on, and the other just a daily driver. Im trying to get him to give me more information but his english is horrible =) . He is from Japan, and hes quite the reputable one here when its comes to the Rotary engines..

just letting you know..

pp13bnos

I live around 30ish miles south of Portland Oregon. I dumped the 110 in my fuel tank at home. That brought my gas guage upto around almost 1/2 a tank. Drove north, picked up my dad, and whent to Portland (Groundzero motorsports) for the dyno session.

I have no doubt that n/a rotarys have allways like the lowest octance possiable (Within reason of course.) I've owned and driven nothing but rotary cars my entire life. All my older cars allways received 87 octane, unless boosted, or running nitrous.

On the dyno, I don't know if his car started picking up some detintaion and pulled some timing out or what. I'm just telling you guys, my 8 made more rwhp and made higher peak power than a similiar car with lower octane. Will this happen in all the time? I have no idea. I'm just relating what happend to me. Incase anyone was wondering, I was driving bolth cars, (Once again, I'm good friends with Ralph.) and did the long push, DSC off.

CJ

Mikelikes2drive

so low octane it is?

Rick

Perfect timing for a new octane thread. For the last few months I have been using 89 octane in my 8 and the engine has worked perfect every time under WOT. last week I decide to give 87 octane another try. Two days later, using 87 octane, I ran the 8 three times WOT and each time I heard 3-6 knocks. I think my 8 is only going to be happy using a minimum of 89 octane.

thered1996

Again, I can't resist a comment (to quote a favorite film, 'milk and cookies keeping you awake, Sebastian?')

I may be wrong but three factors argue for high-octane fuel in my mind:

- for 20 years (wow...I've waited a long time to make such a claim!) I've run nothing but premium fuel in my cars and have never had a fuel system-related failure. This includes injectors and carb jets.

- engines running higher octane fuel run cooler. Summer is coming to North America -- only a handful of 8 owners have summer driving experience. My understanding of the under-hood conditions on RX Mazdas can be summed in a word: hot.

- My grandfather was an 'oil & gas' man, he knew something of the practices of refineries after supplying them with crude oil for 40 years. He ran only premium gas from one of the 'seven sisters' (Exxon, Amoco, and Chevron are all that remain, I think) as they had the highest production standards. Bottom line: avoid convenience store gas -- they buy from the lowest bidder. Seek stations with the newest tanks, there's less crud. Basically, you get what you pay for.

RX8Z

THERED,

you make good points, but youre forgetting the most important part of the puzzle... your arguments work only towards piston engines, the rx8 is not.

I really dont see any other facts stating that higher premium fuels makes the rotary a better performer, and from history and experience, na rotaries do not need high octane fuels at all.

as for higher octane running cooler? I never heard that but im open to anything..

z

thered1996

Almost everyting you'd ever want to know about gasoline is here:

http://www.faqs.org/faqs/autos/gasoline-faq/part1/

Sections 4.12 (Are brands different?), 7.6 (What is the effect of temperature and Load?), and 7.7 (What is the effect of engine speed?) are significant.

While the rotary is not a piston engine, it still operates on the same principles of intake, compression, ingnition, and exhaust. They also use gasoline as fuel.

My understanding of gasoline refiners has always been 'you get what you pay for'...both in terms of quality and additives. To produce a high-octane fuel, greater care must be excercised. Gas with no additives would run 20 to 60 on the RON scale.

Further, personal experience with high performance/compression engines (much of which was gained during Florida summers) has always indicated that higher octane fuels run cooler. Info in the above-referenced FAQ seems to support this observation.

Whether cooler operating characteristics are desirable in the 8 remains to be seen. Overall, I would prefer to err on the cool side leaving the option of higher temps under greater performance demands.

If you're running the lowest octane possible, the engine management system may reduce the engine output when higher demands are put on the engine.

Nubo

Blade Runner!

pp13bnos

I guess it'll be up to each person to make the high or low octane call. But when I head to the track, I'll be running some race gas. BTW, I also noticed that Judge Ito, also made more rwhp on race gas vs. pump gas. CJ

flatso

Lower octane article




Highlights from the article:

Marti Mayne once fueled her low-octane Subaru with high-octane gas. When prices dropped earlier this year, she stuck with cheaper fuel because "I don't think that my car runs any differently on high, medium or lower grade."

She's right. Engines designed for regular fuel don't improve on premium and sometimes run worse. And today's engines designed for premium run fine on regular, too, their makers say, though power declines slightly.

Prejudice and preference aside, engineers, scientists and the federal government say there's little need for premium.

All Porsche engines are designed for premium, too, but it's not available everywhere. "Our cars must be able to drive all over the world, and so we are able to run on regular," says Jakob Neusser, director of powertrain development at Porsche's research and development center in Weissach, Germany. "You don't have to feel that a mechanical problem or anything else will happen" using regular gas, even in the highest-performance, regular-production Porsches.

Premium, in fact, sometimes is worse fuel than regular. It resists knock because it's harder to ignite than lower-octane fuels. As a result, some engines won't start as quickly or run as smoothly on premium, notes Gibbs, the SAE fuel expert.

High-test does have a potential fuel economy benefit. It is slightly denser than lower-octane gas, meaning there's a little more energy in a gallon. But the small difference is hard to measure in real-world use, and that same density can contribute to undesirable buildup of waste products inside the engine.

No data show that engines designed strictly for regular run better or longer on premium.

"There is no gain. You're wasting money," insists Jim Blenkarn, in charge of powertrains at Nissan in the USA.

By James R. Healey, USA TODAY
http://www2.autospies.com/article/in...9&categoryId=9