Maybe we should just rename this site the Male Ego Pi**ing Contest Message Board. Seriously, though, it is good to get varying opinions (mixed with a little bit of fact every now and then) on all the subjects here. I just wish some people wouldn't make it, or take it, so personal.

 

Okay, help out this simpleton, namely me.

If you say high octane gas requires a higher temperature than lower octane gas to burn (explode) and the ignition comes from a sparkplug with the same spark, then the question is, "Is this increased temperature required to make high octane burn instantaneous or does it take longer to build up?"

Another question. If you put higher octane gas in a pinging engine, the pinging usually stops. The pinging in most cases is caused by hot spots in the cylinder, usually built up carbon.

You inject lower octane gas into that cylinder and that hotspot makes the gas explode at, for argument's sake, 7º BTDC and you get a pinging. Now, you inject high octane into that same cylinder and the gas explodes when the spark plug fires at 5º BTDC. Wouldn't you say that the low octane stuff exploded sooner than the high octane stuff?

If you take and engine and set the timing to burn low octane gas to just where it doesn't ping, then you put in high octane gas, you can advance the timing further, correct? Stated a different way, if you burn high octane in your engine and you set the timing to just where it stops pinging, then you switch to lower octane gas, what must you do? You must retard the timing otherwise the engine will ping, correct? So in this particular engine, when you switched to lower octane, you had to shorten the time of ignition to where it's closer to TDC, correct? Doesn't that mean the lower octane stuff takes less time to burn than the high octane stuff?

In my book, if two things leave a starting point at the same time, but one gets there faster (explodes first), then one is faster and one is slower.

Personally, I think the original poster is just nitpicking and making things more complicated than they need to be and others are just jumping on the bandwagon to try and discredit one of the most valuable contributors to this board.

 

Personally Dennis I don't see it as nitpicking, but I do see the whole debate as miniscule in significance. The point about increased polutants being released running a chip.. I just don't buy it, because how could they become 50 states emissions legal if it increased polutant output?

I'm not saying that it isn't possible, just that the increase is probably barely measureable. There does seem to be a regiment of attacks on chips in general lately. Besides BeastRider, there's Factory_Tech who's going around on the Tranny forum telling folks that chips are bad for their trannies.

This time around I'm much happier with my chip than I was on my 4.6L, however my gas mileage has gone down about 1/2 mpg whish is kind of a bummer. (I've been driving like a grannie lately too)

 

Do you have a tick in your shorts? More complicated than they need to be? If you wish to live in ignorance, or in partial understanding, then that is fine for you, but I for one wish to know as much as I can.

I don't challenge the assertions of Mike T. to discredit him, as much as I do to insure that both he and I have the greatest possible understanding of a very complex issue. And, I don't see that Mike has taken any offense... as a pro, he has got to be willing to be open to all avenues of investigation, or pretty soon he won't be a pro.

To answer the specifics in your post

This question comes from the wrong approach. It is a fact that high octane gas burns spontaneously only when a higher temp is reached. Whether that temp is reached slowly or quickly is irrelevant. What is relevant is that high octane resists pre detonation caused by hot spots that would ignite regular gas.

Certainly, but you are confusing the point at which gasoline is ignited (ignition timing) with how fast the gasoline allegedly burns. The real question is, "after being ignited under the same conditions, which takes longer to burn?". And, as you will see in my next post, the answer is premium and regular burn at the same rate.

No, once again it only means that you have changed the point at which the gasoline is ignited. The burn rate is unaffected. You are assuming that if you start the burn at 10 degrees BTDC, that this charge will burn longer than a charge started at 5 degrees BTDC but this isn't true (with exceptions... I told you this was complex).

Well, your book is wrong. The fact is, if premium and regular are ignited with the same mixture and at the same point in the ignition cycle, they will burn at the same rate... see my next post for evidence.

I'm sorry you think it is nit picking. I don't attack Mike, I think he adds a great deal of useful information to this board. At the same time, I believe in fact, not opinion. I cite my sources in the next post. You can discredit my source, you can provide an alternate source, but anything else is BS. And, I'll ask Mike to do the same. If he thinks premium gas burns slower, than cite the evidence. Saying, "100's of professionals" aint evidence.

Bye

 

Folks, How come I can't make money writing on the F150 board? I've been too busy until now to complete my rebuttal to Mike's slow gas response, so here goes.

Mike, I have reviewed your post at length, and I cannot find evidence to support your assertion that it takes premium gas longer to burn than regular. Getting a “check engine” light doesn’t indicate that premium burns slower than regular, although it might indicate that the chemical composition of premium (and the exhaust byproducts) is sufficiently different to cause the engine sensors to think something is wrong, unless they are reprogrammed.

You have spent a great deal of time reviewing “fuel curves” and by this I take it you mean the duration and quantity of fuel that is injected into the intake manifold at the time the intake valve is open. Of the three basic factors that can be controlled in engine operation, valve timing, ignition timing, and fuel/air mixture, only ignition timing and fuel/air mixture can be readily controlled across a wide range of operating conditions. Perhaps when solenoid controlled valves become a reality, we will be able to step to the next level of engine performance.

The settings of ignition timing and fuel/air mixtures are governed by the state of the engine. A control module which monitors only two aspects of the engine state is a 2D chip (about all the earliest ignition systems could do), while modern advanced chips like the Superchip measure RPM, engine temps, manifold pressures, exhaust gas composition, throttle position, and intake air temps in order to compute the optimum ignition timing and fuel air mixture. Mike, I’d be real interested in a list of all the factors that the Superchip uses in making its decisions.

It is important to note that no matter what the fuel curve is, all of the fuel must be injected into the intake manifold BEFORE the intake valve closes and the compression stroke begins. The fuel curves cannot directly affect the burn because in fact, the burn cannot commence until the intake valve is closed and the compression stroke has begun. So, the question becomes, “Is the difference in burn that Mike observes the result of ‘slow’ burning premium, or is it the result of altered ignition timing and fuel/air mixture?” For reasons of chemistry, I say it must be ignition timing and fuel/air mixture.

The real question is what happens once the intake valve closes, the air/fuel mixture is compressed, and the spark is fired. Now, we are talking chemistry of a reaction (oxidation in this case). All the chemical facts point to the conclusion that high octane gasoline (premium) must burn as fast as regular.

I refer you the the FAQ that I have found most definitive on the questions of gasoline.

http://www.faqs.org/faqs/autos/gasol.../preamble.html

I have found that this FAQ has been distributed extensively by many universities and their petroleum engineering departments. I have been unable to find any posts that cite erroneous information in this FAQ. If you find this FAQ to be in error, many people will be very interested in your alternate sources, and you will do a lot of folks a great service.

First, under section 6.1, I offer you the following statement:

"The antiknock ability is related to the "autoignition temperature" of the hydrocarbons. Antiknock ability is _not_ substantially related to:-
1. The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.
2. The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons. Although flame speed does play a minor part, there are many other factors that are far more important. ( such as compression ratio, stoichiometry, combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.) Flame speed does not correlate with octane.

This is correlated by reviewing the basic characteristics of both heptane and octane. In section 4.9 we discover that the heat of combustion of heptane and octane are very nearly identical. Hence there is no physical process based on physical properties that could cause a different rate of burn.

Fuel State Heat of Combustion Research Motor
MJ/kg Octane Octane
n-heptane l 44.592 0 0
g 44.955
i-octane l 44.374 100 100
g 44.682
toluene l 40.554 124* (111) 112* (94)
g 40.967
2-methylbutene-2 44.720 176* (113) 141* (81)


Next, under section 4.11, the author states:

"Combustion Characteristics
As gasolines contain mainly hydrocarbons, the only significant variable between different grades is the octane rating of the fuel, as most other properties are similar. Octane is discussed in detail in Section 6. There are only slight differences in combustion temperatures ( most are around 2000C in isobaric adiabatic combustion [45]). Note that the actual temperature in the combustion chamber is also determined by other factors,
such as load and engine design. The addition of oxygenates changes the pre-flame reaction pathways, and also reduces the energy content of the fuel. The levels of oxygen in the fuel is regulated according to regional air quality standards."

Simply put, gasoline burns just about the same, no matter what is in it. As a final example, take a look at the characteristics of octane and heptane from section 6.1:

Fuel Melting Point Boiling Point Density Vaporisation
normal heptane -90.7 98.4 0.684 .365 @ 25C
iso octane -107.45 99.3 0.6919 .308 @ 25C

The numbers are nearly identical.

So, from a chemistry point of view, different rates of burn based upon octane are a myth. What this means is that when Mike observes different burn characteristics when the Superchip and premium are used, the difference is due to timing, load, and fuel/air mix, not the gasoline itself.

Mike, if you disagree with this assessment of what you see, then I encourage you to post data that supports your position. The burning of gasoline in an internal combustion engine is a complex process, and if you have more data about how it works, I'd love to see it. However, anecdotal evidence won't cut it.

 

There are only two reasons that any sane engine manufacturer would retard the timing on an engine.

a) you can use lower octane fuel
b) it significantly cuts back on the production of oxides of nitrogen... if you don't believe this, I will be happy to send you multiple engine studies that prove this up.

So... engine manufacturers retard the timing because only crappy 87 octane is available. A side benefit is that N02 and N03 emissions go way down. Why? Retarded timing results in reduced cylinder head temps which reduces N0X output.

Enter the Superchip. It has been approved in California, and if it works there, it works anywhere. I'm impressed with it because if you simply advanced your timing (which you can't), you would definitely blow CARB standards.

Please be assured that I am not knocking the Superchip at all, and I am actively considering a flip chip. Ford has got to reach a compromise in the chips it develops... if you want to run on the edge instead of the middle of the pack, then the chip makes sense... if alters those elements that would make the average joe think his truck aint runnin' right.

And clearly, since the chip requires the use of premium... the flip chip gets marginal gains with regular, it is ignition timing that makes all the difference... the chip maximizes the potential of advanced timing thru fuel/air mix and drive train control.

 

Beast Rider,

Just for reference, I saw the thread as discussion, not anyone attacking a product or person.


Interesting links, although I must admit more in depth than I need to know!

Several points to those on both sides of the discussion........

Personally I've used premium on a standard program with no problems. I also got a (very) slight mileage increase. The fact that different additives are used in the premium fuel could account for this. The difference in additives, etc could also change emissions, generated heat and other such variables, which could trigger a "check engine" light if out of standard operating limits. Since the mileage increased with the stock timing, I would tend to think that there was more energy released, due to the change in overall fuel formulation.

As far as changing fuel curves, it seems to me this in itself would not change burn time. Changing a mixture without changing timing would no doubt affect output and emissions. However, the chip changes both. Assuming that the chip would increase the fuel injected then this, along with increased timing would in my opinion create a longer burn cycle. If the burn ends at a given point after TDC, but starts earlier it would seem to me that the burn cycle has taken more time as measured in degrees of crank rotation.


Having not seen this as any attack and being open minded to all stated facts and opinions, it seems to me that you both are right, but just not comparing apples to apples.

 

Basically, all things being equal in an engine, you can set the ignition of an engine to fire the plugs earlier when you're using high octane gas vs. low octane gas, correct?

Now, if you advanced the timing on an engine to a certain point that's running low octane, pinging would be the result, correct?

In other words if you advanced the timing too much, the gasoline would burn/explode too early, correct?

In the engine, air and gasoline liquid/vapor compresses. As it's compressing, at some point before it reaches it's maximum compression, Top Dead Center (TDC) the ignition system fires the plug. This causes the air/gas mixture to start burning from the plug down to the face of the piston.

Now, you wouldn't want the air/gas mixture to fully burn until after the piston is past TDC, cause if it fired and burned completely BEFORE it reached TDC, then the piston would, logically speaking, want to go back down before it reaches the top. Now, if one cylinder out of 8 did this, the engine would keep running and probably destroy that one cylinder, however, if all the cylinders did this, the engine wouldn't run. In fact, it would run backwards. This condition was "lovingly" referred to as dieseling. Something you don't hardly ever see in modern cars. Not even sure if it's possible in fuel injected cars, but definitely can happen with carb equipped engines.

Anyway, if the engine is pinging because the gasoline is burning too early you can do a couple of things. You can retard the timing so that the plugs fire later or you can increase the octane.

Explain to me why increasing the octane without changing the timing can eliminate pinging? If low and high octane gas burns at the same rate, how come you can advance the timing quite a lot with high octane when compared to running low octane. If what you're saying about the two gasolines burning at the same rate is true, then why doesn't the high octane stuff burn too early and cause problems with the engine's performance? I don't think the ignition coils put out a hotter spark to ignite higher octane fuel. In fact, they both start burning at the same time, according to you. So, what accounts for the fact that high octane gas can be fired earlier than low octane can? If they burn at the same rate, then the time that the plug fires in relation to the piston position shouldn't matter. Clearly, however, it does.

When I was in high school, we didn't have fuel injected engines, other than diesels. We used to race our cars and boats. One of the tricks we used to do was we'd fill the tanks with high octane gas and advance the timing to get max power at full throttle. This was done without a timing light. You keep advancing the distributor until power drops off, then you back it off. That was one way we would get our times down. Then, after the races, we'd want to go back to lower octane gas for everyday driving/boating. We'd have to retard the timing quite a bit. On the boats, we cold retard it just to the point where performance didn't drop off. With the cars, we'd use a timing light and put everything back to specs. The fuel delivery was thru carburetors. The amount of gas delivery was limited by the size of the jets. There was a finite amount of air and gas that could be sucked thru the carbs no matter what kind of gas we were running. So, the only change to get better performance out of high octane gas was thru a change in the timing. Just thought I'd throw this old experience in to see how you explain the increase in power.

 

Hi Beastrider, et al,

Before preparing a response to you, I spoke with a number of sources, ranging from within API (American Petroleum Institute) to various tuners at a couple of different chipmakers, and a couple of powertrain engineers at different automakers.

Gasolines are highly complex chemical compound mixtures that have to meet widely varying performance requirements over an extremely wide range of operating environments & conditions.

What is the Octane Rating? There seems to be much confusion & misinformation about what the octane number on the gas pump actually is, what it reflects, means, etc.

Octane, by definition, is the resistance to detonation, and the resistance to initiate burn under those conditions in the combustion chamber goes hand-in-hand. This is debated and argued endlessly, but the fact of the matter is that higher octane fuels are generally harder to ignite in the combustion chamber, and burn more slowly in terms of the time (duration) it takes to reach optimum cylinder pressure at the time of optimal piston position in the bore (after TDC) than fuels with a lower octane. Higher octane allows for better control of the burn in engines that are either mechanically configured (as in high compression) or specifically tuned for (as in the use of a performance chip) the use of premium gasoline. Conversely, engines that are specifically tuned for the use of 87 octane will many times produce less power, higher emissions and worse fuel mileage when fed significantly higher octane gasoline, due to these very same characteristics.

The octane rating on gas pumps must be visibly displayed using the mandatory yellow octane rating stickers found on virtually all gas pumps. This octane rating is the average of both the Motors (MON) and the Research (RON) method of determining octane. The octane rating seen on the pump is the minimum octane value the gasoline will have. Some states do allow a bit more variance than others, but by and large, the octane rating you see on the gas pump means that what you’re putting in the tank will be at least that octane number. Both of these methods of rating the octane value use not a normal automobile in everyday driving conditions, but instead use a special very low-rpm single-cylinder test engine that has a variable (adjustable) compression ratio. The RON (Research method) measures the knock resistance of a fuel during low rpm (about 900 rpm) & very light load conditions. The MON (Motors method) uses slightly higher rpms (still very low, about 1600 rpm) and higher load conditions. The MON number will always be lower than the RON number, and here in America the octane ratings seen on the pumps is the average of those 2 numbers.

When the tuning of a gasoline engine is changed from being optimized for the use of 87 octane to being optimized for the use of “premium” gasoline, more power is produced and usually a small increase in combustion efficiency can be achieved, assuming proper tuning techniques are employed. When this is done, there is also the potential for a small improvement in fuel efficiency, or gas mileage.

Many people have assuming incorrectly that “gas is gas”, and they’re all the same, so always use the cheapest possible gasoline. Wrong! While there is indeed much “sharing” of base gasoline stocks among numerous oil companies, there are indeed differences in fuel quality between brands of gas, and even between the same brand of gas in different areas of the country. There are differences in various additive packages that have been shown to not only make a difference in how clean the fuel delivery & intake valves remain, but also differences in the actual performance of the engine as well as gas mileage. There will be variances in actual energy content from brand to brand, but the differences in actual energy content are never rated on the pump, nor will the oil companies generally tell you what the energy content of any given refinery run actually is. The best method the “layman” has of trying to determine the relative energy content of their various local brands of gasoline is to track consumption, via strict & accurate calculation of MPG. Burn 3-5 tanks of each brand, under the same approximate driving conditions, and track the MPG with each different source. The gas delivering the highest MPG numbers, all else being equal, is generally going to be the gasoline with the highest relative energy content.

The FAQ article posted does indeed contain some excellent information, however, it must be remembered that it is a compilation of many different sources, and thus contains some conflicting information.

Quote:

The behaviour of manufactured gasolines in octane rating engines can be predicted, using previous octane ratings of special blends intended to determine how a particular refinery stream responds to an octane-enhancing additive.

Response:

This would seem to indicate that changing octane does indeed bring about predictable changes in “behaviour”.

Quote:

Simply put, the octane rating of the fuel reflects the ability of the
unburnt end gases to resist spontaneous autoignition under the engine test conditions used.

Response:

This is important, as not only is that not a complete definition of octane (admittedly, it does say "simply put") and all it's characteristics, this is also “under the engine test conditions used”, meaning the special purpose single-cylinder engine that runs at very low rpms, 900-1600 or so. These are not the same conditions found in automotive engines in everyday driving, they are simply controlled test conditions using a special-purpose single-cylinder engine with a variable compression ratio, designed to provide the same basic test "environment" just so that the same consistent test method & environment is used each time.

Quote:

Although flame speed does play a minor part………

Response:

BINGO! Yes indeed, just as we’ve been saying.

Quote:

The ignition advance map is partly determined by the fuel the engine is intended to use. The timing of the spark is advanced sufficiently to ensure that the fuel-air mixture burns in such a way that maximum pressure of the burning charge is about 15-20 degree after TDC. The actual ignition timing to achieve the maximum pressure from normal combustion of gasoline will depend mainly on the speed of the engine and the flame propagation rates in the engine.

Response:

Amen! This also causes a need for changing the effective amount of time available for the fuel to burn as a result, and it is those specific changes that we are referring to when we say that the fuel curves require alteration for proper tuning to achieve most efficient combustion, power, driveability, emissions & fuel consumption when the engine is re-tuned specifically for high octane gasoline via a performance chip.

This must be dealt with by the automakers and aftermarket tuners alike, to come up with an optimal combination of spark advance and air/fuel ratio for each throttle position, engine rpm & load point. Exactly *what* adjustments are made depends on the exact application & vehicle configuration as well as octane level of fuel being used.

Here is a quote that I especially liked in that FAQ, something we've been saying for years:

8.5 Can I improve fuel economy by using quality gasolines?

Yes, several manufacturers have demonstrated that their new gasoline additive packages are more effective than traditional gasoline formulations.

Response:

We couldn’t agree more, and in this article, it cites Texaco, one of our favorite brands of gasoline, and the legal battle they had with Chevron over the advertising of the results of their fuel additive packages. The point being, there is indeed a difference in fuel quality, and it pays to use the best quality fuels available. You’ll get better performance and fuel mileage, and in some cases slightly lowered emissions as well.

Obviously we've covered several points in addition to the single specific issue raised by BeastRider, however, I felt they were points that others may liek to know about gasolines in general, so they were included.

I think it's important to remember that it is not my purpose to try and convince you or "prove" anything to you, nor do I have any such responsibility; this is just to give you some perspective from the professionals who actually tune these complex computer-controlled powertrains for various levels of octane and all manner of configurations, etc. What you choose to believe is up to you.

I hope this gives you a little bit clearer picture, & I wish you well!

 

there is way to much info about gas for this average laymen and trying to underststand all of what was written by everyone is givin me a headache.

 

on a number of things you said, you are missing or incorrect on some key elements that make the conclusions you draw, incorrect. Please let me explain.

First, in most engine setups, the spark plug fires BEFORE the piston reaches TDC even at idle and especially at speed. It takes tome for the flame front to travel and make the power and in that time, generally the piston is finishing its travel. The trick is to have that timing advance just enough so that you don't fight the piston during the upstroke, i.e., have the flame front/compression wave from the explosion reach the piston top just at TDC to push that baby down. You don't want it to freewheel beyond TDC if you can avoid it because then the compression wave is chasing the piston and you waste power.

Second, "dieseling", at least in my experience (and I have had it happen in a really bad way) is when the fuel/air mixture ignites without the aid of any spark. Pinging is not necessarily the ignition of all the fuel/air mixture early but the ignition of pockets early or perhaps even sumultaneously but in a chaotic manner. What is supposed to happen is that there is a clearly defined compression wave/flame front that travels from the bowl of the head to the top of the piston in one smoth front, not a byunch from all over the cylinder & head (what happens when you have bad hotspotting).

And I think there is an issue of misunderstanding or perhaps just using the terms wrong with repsect to octane rating affecting burn rate. Octane is just some goofy number that roughly measures the gasolines resistance to predetonation and perhaps at one time, was linked directly to energy content but isn't anymore. Why is entergy content important? Because this is what affects the BTUs that a given amount of fule will produce. The BTUs control how much energy you can get out of the given amount of fuel and thus how much power that energy can produce (all other things held equal).

To be precise, what really matters is the rate at which the flame front travels NOT how "fast" the gasoline ignites. So what would make a flame front move faster or slower? Well, there are a bucn of things but for this discussion, ponder this. The fuel/air misxture has a temperature at which it combusts. The temperature of the mixture is not uniform throughout the combustion chamber even while under full pressure. The combustion of the gasoline nearest the plug is ignited because a very small portion (near the spark) has energy imparted to it from the spark raising it above combustion temperature. This reaction is exothermic and releases energy (BTUs) to surrounding spaces igniting more gas.

This is how the flame front works. Now a fuel that released more BTUs per unit volume would release more energy and thus raise the temperature for a larger volume of nearby fuel or raising the temperature of a fixed volume of fuel faster. So it would follow that all other thigns being equal (like flash point), a higher energy fuel would have a "faster burn".

So lets look at higher octane fuel burning slower. Let's assume (a safe one) that a gasoline manufacturer puts in a non-flammable additive, oh like lead, into a fuel to reduce its combustability (reduction in pinging). What has happened to that fuel? Well for any given volume, the energy has been reduced since the additive is non-energy producing. This would result in a slower flame front. Since the additive increased the "octane" rating of the fuel, this means that a higher octane fuel :burns slower".

Does all this make sense? I think that there are a lot of "common" terms that get thrown around that are correct in their usage pertinent to what to do0 with a motor that are not necessarily correct in the scientific. I also believe that there are great theories in how things work that are just not as neat when you toss in 200 moving parts. So therefore in a manner of speaking, all participants in this conversation have been right & wrong at points. Can we all just agree that there are good points around and be done with it?

By the way, I have absolutely no real clue if anything I said above is correct or relavent in the real world, i.e., I am not an SAE mechanic, drag race tuner, etc. Nor am I a petroleum engineer, chemist, mechanical engineer, or tobacconist. I ahve just read a few books and busted a few knuckles. This stuff seems to make sense to me, sometimes. So take my dissertation for what it is worth and consider what you paid for it, nothing!

Chuck

 

Making some of my points early because I was too slow at typing!

Chuck
P.S. You're still wrong

 

Does anyone know what an aneurism feels like?!?

 

(yawn)

 

By this response should I conclude that you are
a. A smartAzz
b. An arorgant Pr!ck
c. not one of my fans
d. a narcoleptic
e. some combination of the above

(note that bored with the discussion is omitted because saying nothing would have been sufficient)

Sorry if I bored you. Sorry if my ideas of what happens in the combustion chamber are as whacked as what I think goes on in a transmission (from the last time I tried to discuss something with you). But it seems to make sense to me.

I can say that your response does seem a bit like 'b'. Don't know what I have done to deserve the response.

Chuck