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

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

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:
http://www.rx8club.com/showthread.php?s=&threadid=15645&highlight=octane
It contains a lot of information that might interest you.

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.

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

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

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

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

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

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.

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

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.

This is a strongly related thread:
http://www.rx8club.com/showthread.php?s=&threadid=20976

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..

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

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..

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

so low octane it is?

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.

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.

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

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.

Originally posted by thered1996
Again, I can't resist a comment (to quote a favorite film, 'milk and cookies keeping you awake, Sebastian?')

Blade Runner! :cool:

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

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/index.asp?articleId=2749&categoryId=9

After trying all available brands of gas in my area (Inland Empire in Southern California) and all 3 available octanes, I've come to the conclusion that gas brand matters more than octane rating. I run 87 regular in my 8 (6mt) and the car runs great. I use Shell gas exclusively now (will use Chevron in a pinch) and although Shell regular is more expensive than discount gas, it outperforms them all at any octane. I found Arco gas, even their premium, to be the worst....it was the cheapest...in every way. Costco gas didn't work very well either; Sam's Club gas was ok but not great.

Bottom line? Don't bother with cheap gas at any octane. If you haven't tried it yet, try a couple tanks of Shell regular and see how it works for you. It may very well be that different cars might need 89 or 91 octane because of production variances in construction, but the average RX8 should be just fine with Shell regular; and you'll save money too.

Ole Spiff,
I'm using 87 octane Shell too. If I may make one more suggestion ....... if you decide on Shell and want to save some $$$, consider getting a free Shell credit card which will save you 5% off Shell purchases and 1% of your non-Shell purchases can be used towards you Shell purchases. You can usually find applications at the stations or check Shell's web site.

rx8cited

Well, I'm a new RX-8 (automatic) owner and am getting 12.5 mpg in the city (L.A.)! I've been using the recommended high octane fuel (at $2.35 a gallon!!!) and think I should be bankrupt by next winter.

I'm going to try Shell 87 octane for 2 tanks in a row and see what the heck happens. Fingers crossed. This 12.5 is very upsetting.

Granted, I only have 400 miles on the car and they say the engine gets better with miles... But, please, 12.5?

Originally posted by misterdc
Well, I'm a new RX-8 (automatic) owner and am getting 12.5 mpg in the city (L.A.)! I've been using the recommended high octane fuel (at $2.35 a gallon!!!) and think I should be bankrupt by next winter.

I'm going to try Shell 87 octane for 2 tanks in a row and see what the heck happens. Fingers crossed. This 12.5 is very upsetting.

Granted, I only have 400 miles on the car and they say the engine gets better with miles... But, please, 12.5?

it sounds like you're havin' a pretty serious problem there.

there was one member a while ago who had a temp sensor issue, and the engine wouldn't come out of cold-start mode and he couldn't get better than 12mpg or something.

you may be having a malfunction of something. see your dealer about it if it persists and is very consistantly low.

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


we need to remember the purpose of a dyno. it is a tool to measure horsepower. you could take two identical cars and they will have a different hp number. the correct way to use a dyno is: take your car and make a baseline run and note the number. make the changes you're going to make, then run it again and note the number. if it increased good, if it decreased, then find out why.

i go round and round about this with my motorcycle friends as well.

on point of octane, the octane rating only means the point in which it detonates. if you use a gas with a higher octane than needed, the engine is not detonating efficiently.

my .02, but i could be all wet.........since it rained 5" last night.

yamajj

With regards to dyno readings, keep in mind that mass production cars and engines are not by any means perfect. There is a variable called "tolerance" which means an assembly can be within a certain percentage of blueprint spec and still be acceptable for production purposes. This is going to produce some cars that are better than others off the same assembly line....by a small margin. Every once in a while you'll get a car that gets lucky and is VERY close to blueprint; it will have great power and performance; and on the other side of that coin you'll get one that's unlucky and is pretty far off and those are usually considered a "lemon."

This means you're going to get a variance of power and performance abilities from one car to the next. The only way to "fix" that would be to spend the time and money to "blueprint" your engine yourself; which is the process of bringing it to exact blueprint spec. Theoretically this would give you an engine that produces exactly the power rating that the blueprint calls for; anything less than blueprint will give you less power. This is why some cars have slightly more power than others that have come from the same assembly line.

Manufacturers could tighten their tolerances but that would slow things down during production and the price of the car would go up significantly. This is why hand-built race cars are so much more expensive than a mass-production car; it's not only the components that cost more, it's the amount of time and labor involved to make it exactly to spec.

So based on all the above, a 5 to 6 horsepower difference between one 8 or the other is normal and doesn't mean there's anything wrong with the cars or the testing method. This also means some cars will not respond well to 87 octane because they are probably on the edge of tolerance, while others will respond very well because they are closer to spec. Apparently I got lucky; my car runs great with it. Others claim pinging and knocking and a loss of performance. Try it yourself and if it works, great. If not, then go to the next higher octane until your car runs okay. But as I've stated earlier, get a good brand of gas; not cheapo gas. I recommend Shell here on the west coast of the U.S., but there may be an equally good brand in other areas...but go with a good brand; don't get cheap gas!

The main difference between octanes is how fast they burn. The higher the rating, the slower the fuel burns. There is NO power to be gained by running a higher octane than what the factory recommendation is. The factory knows what octane will work best in conjunction with an engines timing.

The octane rating system was developed to standardize the anti-knock quality of gas based on, not the performace level or quality of the gas. The idea that higher octane is better perfoming is pure marketing B.S. All octanes go through the same refinement process and contain the same addatives and detergents. If a manufacture says to run 87, running a higher octance is NOT needed, unless there is a problem with your engine, or if you have advanced your timing more than a few degrees. Infact, depending on the engine you may lose HP by doing this. Of course this means that you should never run a lower octance than recommended because it very well could cause knock. I believe that is where all the confushion begain about running higher octane as being safer.

I just got through all of this for the 2nd time in my college automtive courses (no I didn't fail a class, they cover fuel in 2 different classes).

Since my above-referenced thread has mysteriously dissapeared, I will post up what I have written before:

Gasoline engines of all types are driven by the same process - combustion.

Combustion is the rapid release of energy from a fuel - in this case gasoline.
A finite quantity of gasoline contains an equally finite amount of energy, which can be released by combining it with a specific quantity of oxygen at an absolute ratio.
1 kilogram of gasoline contains 43 megajoules of energy that can be released via oxygen at a ratio of 1:15.179 (a ratio referred to as "stoichiomentric"). That is about 41,700 BTUs. Plenty.
The trick with an internal combustion engine (ICE), whether it be rotary or other wise, is to control that combustion in space and time.
We do this by causing the combustion process to occur in the combustion chamber at a precise time and OVER a precise quantity of time to convert that heat into torque.
To effect this level of control, we must take a fixed quantity of space (about 650 ml in the case of the 13b-MSP), fill it with a quantity of gas and air as proscribed by the above ratio, compress it to a precise degree and ignite it at precisely the right time as to cause the maximum pressure increase resultant from that combustion to occur at the time of maximum delta for the combustion chamber's swept cyclic volume (that is to say at the precise moment that the combustion chamber is starting to get bigger again after it just got done getting smaller to compress the charge).
The beauty of this process is that it can occur completely independent of any change in factors in the outside world - temperature, pressure, altitude, pollution, humidity, whatever - as long as we can be
assured that these conditions inside the combustion chamber are constant.

The problem is, we can't.

Because the process of getting a fixed volume of O2 into the combustion chamber at a proscribed density (meaning temperature via Avagadro) is complicated by the fact that this air is supplied by the available atmosphere, we are straddled with the effects of varying density on the combustion charge.
What that means is we must compensate for the volatility of gasoline as it responds to the varying charge densities. At differing charge densities, the amount of energy necessary to start the combustion process and the time it takes to complete the combustion process changes in a not so linear fashion.
So, what we do is vary the amount of fuel we add and ignite the process on a adjustable schedule based on what information we can obtain about the conditions of the air going into our ICE.
What we measure in the case of the RX-8 to know these conditions are these:

Air Flow
Intake Air Temperature
Barometric Pressure
Coolant Temperature
Throttle Position
Eccentric Shaft Position

By computing all of these measurements together, the engine control unit (ECU - sometimes called PCM for powertrain control module) can determine APPROXIMATELY the density of the air charge in the combustion chamber at any given time. It is a shame, really, that there is no way to measure the density directly or we could forgo all of this.
Two factors that can't be measured by the above methods are important to the whole equation as well.
First is volumetric efficiency (VE) or the amount of air, as a percentage of maximum, that the engine actually ingests as a result of the physics of mass and inertia. This number is fixed to some degree and changes at different RPM.
The other is the latent temperature of the actual combustion chamber as a result of the combustion cycles that proceed the cycle under scrutiny at that moment. This changes as a result of RPM as well, but it is also tied to 'load' or the increase of RPM over time as a proportion to charge density.
What that leaves us with is a very crude measurement of the total charge density.
How do we compensate for that?
By conservative 'hedging' on the bet that is ignition timing through advancement and retardation of the onset of the spark and by introducing elements into the gasoline that seek to stabilize its volatility. That is what octane is for and how much it affects the combustion process is measured by various methods including, but not limited to, Research Octane (RON), Motor Octane (MON) and the Anti Knock Index (AKI - and average of the RON and MON numbers). Unfortunately for the average motorist, many other ingredients are added to the fuel we use to affect its environmental impact that are not directly computed into the AKI. Ingredients are added to lower the boiling point and vapor point, reduce the hydrophilic nature of gas and reduce the amount of oxides of nitrogen after the combustion process. Many, if not most, of these ingredients change the combustion process in ways that may not be consistent from sample to sample. They also alter the total energy content of the fuel itself.

As it has been mentioned previously in this thread, having the ignition process starting at the wrong time (especially too soon) is a bad thing and can (especially in the case of the rotary ICE) quickly destroy a motor. So what is done, more often than not, is to err on the side of safety and bracket the combustion process with extra fuel and start the ignition with a slightly delayed spark. What this does is lower the temperature of the intake charge and insure that the combustion process is slower and later than optimal and never faster or sooner. Raising the AKI of the fuel used will accomplish the same thing but since the manufacturer of the vehicle can't insure that the fuel used will always have the proper AKI to achieve this or won't contain additives that adversly affect the ignition onset, they don't depend on their octane recommendation alone.
What is done by "tuners" then, is to take into account this margin of error and dial some of it out for more power which can be achieved by charge composition that is closer to optimal. To achieve this, they depend on the operator to use fuel that takes up the slack in AKI and remove some of this extra fuel and spark retardation.
Really, that is all there is to it. How good a tuner can be is dependant on his or her ability and knowledge with respect to the events within the combustion chamber in question. Unfortunately, that knowledge usually comes at the price of some blown-up motors.

1:15.179 (a ratio referred to as "stoichiomentric").
[size=2]
Stoichiometric ratio is actually 14.7xxx:1

Stoichiometric ratio is actually 14.7xxx:1
Actually, no. True stoichiometry occurs at the stated number.
Maximum power tends to occur at 14.7:1.

Stoichiometry refers to the point at which there will be no uncatalyzed gasoline molecules.

Interesting article on this subject. I would think the RX8 is more similar to the M3.

http://www.caranddriver.com/article.asp?section_id=4&article_id=3604&page_number=1

Actually, no. True stoichiometry occurs at the stated number.

Not according to my text books.

Damn... I need a drink... maybe I'll try some Bacardi Black, or would I get drunk faster with Bacardi 151?

Ha! You guys kill me!

Just for shits-&-grins, try the mid-grade! LMAO......

Yep, gonna piss off many folks with this post. Sorry? Hell no...

Not according to my text books.
And which would those be?

14.7:1 is what produces optimum power.
15.2:1 is complete stoichiometry.

The stoichiometric ratio is in fact 14.7:1.http://www.epa.gov/otaq/epg/keyterm.htm
The very first text box. The click the hypertext "stoichiometric" It is understood in chemistry that for gasoline, 14.7:1 is the level for stoichiometry. But I would for my own reasons like to know where you got 15.179:1. Thanks

I always thought the optimal A/F ratio for power in an N/A (piston based) engine was 12:1 through 13:1...with a slight bump in richness @ the torque peak of the engine. (This of course slightly varies engine to engine)

I was under the belief that the optimal mix for "mileage" was 14.7:1, which is why most vehicles try to maintain that mix in closed loop fuel modes.

Stochiometric is shitty anyway...

Combustion is never 100% efficient anyway...

It gets even lower with more overlap.

I believe that 13.5 with an N/A engine is good, and even lower with more overlap, when unbunrt fuel goes straight through the exaust... Combustion is the same, but more fuel is dumped into the exhaust, without ever seeing any spark.

BTW, my all motor 2.4 neon likes 110 octane better that 91 pump gas...even when not pigning... maybe the race gas just burns better... then again, 11.5:1 is not the 10:1 we've got in the '8...

Chris

Im glad some of you guys aren't engineering the fuel injection system! ;)

Air/Fuel ratio is based on pounds of AIR to pounds of FUEL but carbs/injectors are metered (jetted) by volume so changes in fuel can change A/F ratios. A/F Ratios range from about 2:1 for NitroMethane to about 16:1 for gasoline, with 14.7:1 considered the stoichiometric or chemically correct ratio under perfect conditions with normal (non-oxygenated) gasoline (hexane). Gasoline A/F ratios for best power tend to be in the 13.25:1 - 13.75:1 range.

When you get confident with that, take a stab at the correct fuel air ratio for a hydrogen/helium slurry scramjet injection system with respect to altitude and ram air pressure. :D

heheheheheh