There seems to be a lot of misinformation out there about octane and what gasoline should be used in the Acura TL. Let's go over the entire subject.

First of all, the higher the RON (research octane number), the LESS volatile the fuel. The lower the RON, the MORE volatile the fuel. In simple terms, lower octane fuels are easier to ignite than higher octane fuels. If you think different, you are wrong.

Gasoline is known as an aliphatic hydrocarbon. Gasoline is made up of molecules composed of nothing but hydrogen and carbon arranged in chains. Gasoline molecules have from seven to 11 carbons in each chain. Some of the most common configurations are; Octane, Heptane, Nonane and Decane.

When gasoline is burned under ideal conditions, you get carbon dioxide (from the carbon atoms in gasoline), water (from the hydrogen atoms) and lots of heat. A gallon of gasoline contains about 132x106 joules of energy, which is equivalent to 125,000 BTU or 36,650 watt-hours. The internal combustion engine relies on heat or the energy produced from the explosion of the air fuel mixture. What determines power output of any gasoline engine is how efficiently it burns fuel. Air is a limiting factor in power production. However, if we can get more air packed into the cylinder then it must be met with the proper amount of fuel.

Moving on, the chemically correct formula for heptane (which is gasoline) is 14.64:1. Some people say, 14.7:1, I'll except that, but it's really 14.64:1. The ideal Air Fuel Ratio (AFR) is then 14.64:1 or 14.64 parts of air to 1 part fuel. Theoretically, this is the air fuel ratio that the computer would try to maintain under cruise conditions. During wide open throttle (WOT), the AFR is richened from STOICH. All engines run rich at WOT (lean would be any AFR numerically higher than 14.64:1).

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage the pistons, piston ring lands, connecting rods, and many other parts in the engine. Knocking or pinging is bad regardless of how small it is.

Detonation is something different. When detonation occurs it almost always caused by a mechanical problem or simply a lack of fuel in one or more cylinders. Detonation is a large explosion in the cylinder(s) which sends violent shock waves throughout the engine. In most cases, the spark plug is destroyed, but pistons can be damaged as well as connecting rods and the crankshaft. High octane fuel (i.e. 94 octane and 100 octane unleaded gasoline) can handle the most amount of cylinder pressure before igniting. Likewise, lower-octane gas (i.e. "regular" 87-octane gasoline) can handle the least amount of compression before igniting. The amount of heat energy required to ignite high octane fuel is higher than that of a low octane fuel.

The compression ratio of your engine determines the octane rating of the gas you must use in the car. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that adds horsepower without increasing the displacement of the engine. Higher compression ratios have higher cylinder pressures and better throttle response.

When you take crude oil and begin to process it in a refinery, you end up getting hydrocarbon chains of different lengths. These different chain lengths can then be separated from each other and blended to form different fuels. For example, you may have heard of methane, propane and butane. All three of them are hydrocarbons. Methane has just a single carbon atom. Propane has three carbon atoms chained together. Butane has four carbon atoms chained together. Pentane has five, hexane has six, heptane has seven and octane has eight carbons chained together.

Heptane handles compression very poorly. Compress it just a little and it ignites spontaneously. Octane handles compression very well , you can compress it a lot and nothing happens. Eighty-seven-octane gasoline is gasoline that contains 87-percent octane and 13-percent heptane (or some other combination of fuels that has the same performance of the 87/13 combination of octane/heptane). It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio.

During the 1900's it was discovered that you can add a chemical called tetraethyl lead (TEL) to gasoline and significantly improve its octane rating above the octane/heptane combination. Cheaper grades of gasoline could be made usable by adding TEL. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, there were side effects of adding lead to gasoline and I think we are all smart enough to figure out what they were. Leaded fuels are still available today for some high performance piston airplanes and for some race cars. At some drag strips you can find anywhere from 100 to 120 octane LEADED race fuels.

I've heard people say their car made more power with higher octane fuel. That is not exactly true. The higher octane fuel didn't increase the power output. Most likely more spark timing is what increased the power output. Higher octane fuel allowed the engine to be less knock constrained. All supercharged and turbocharged engines are knock constrained, so they require higher octane fuels. Also high cylinder pressures can keep an engine knock constrained, this can also be caused by high compression ratios. Spark timing is critical to achieving maximum power output. 1 degree of spark advance can be worth as much as 4-5 HP and 8-10 lb.-ft. of torque on a supercharged or turbocharged engine.

There are a few Ford vehicles that have knock sensors (KS) and the PCM uses the KS to listen for harmful knock. Since knock sets in well below what any average human can hear, by the time you notice the noise, much of the damage has been done. The PCM detects knock through the KS which is set for a frequency and threaded into the engine block. The actual program of the EEC/PCM is complicated, but for the older EEC-IV Ford systems it works much like this. Talking Wide Open Throttle (WOT) only, there is a function of RPM vs. Timing. This function is then modified based on barometric pressure, coolant temperature and air inlet temperature. This is a given final spark timing value. On some of the older cars there was an Octane Adjust Pin that if shorted (by pulling the bar out) it would subtract 3 degrees of spark timing. It can also be reversed to add spark timing with the proper software changes. The final say is the Knock Sensor(s) and the EEC/PCM has it's final spark timing value.

The newer Ford PCM's ('96 and up EEC-V) have a table of RPM vs. Volumetric Efficiency (VE). VE is basically theoretical air flow over actual air flow or LOAD. So the Mass Airflow sensor must be correct and the transfer function must be correct as well. Most spark timing tables are cryptic and unless you can read hex code and have the engineering software and understanding of the system, you cannot change the factory values. You think you can, you cannot. The amount of time that is required to reverse engineer any given PCM is enormous and while it can be done it takes alot of time and money.

Now there is NO WAY the PCM can distinguish between 87 octane and 94 octane gasoline. Unless you have a custom hybrid fuel system that runs E85 and gasoline with an optical octane sensor, it just doesn't work that way. So if the engineers tuned the engine to make 300 HP (just an example) on 87 octane fuel and the PCM has working knock sensors, switching to 100 octane will not increase the power output to 310 HP. If you think more octane means more power, you are wrong. If your engine is running 87 octane and the knock sensor(s) are tripping then spark timing is being reduced. If enough spark is pulled the engine will feel less responsive, especially under load. Switching to 94 octane brings back the power. The power returned (key word) not from the octane itself, but from the spark timing being put back in. Since higher octane fuel is less volatile, it doesn't ignite as easily.

By using a higher octane fuel, the engine is less likely to ping or knock. Engineers can dial in more spark and gain more power. It also ensures the engine won't ping when loaded with a locked-up torque converter (5AT only), the air conditioning on and climbing a grade. So should you use 94 octane in your 2004-2005 Acura TL? No, you can use it, but you are wasting your money. Using more octane won't hurt anything (unless it's leaded fuel with 100+ octane), but using less octane can be bad. Especially if your engine has hypereutectic pistons. With any engine that has Knock Sensors, using less octane than what is required will almost always set them off and reduce performance. It also reduces efficiency of the engine since after all, what determines power output is how well it burns the fuel. Will fuel economy suffer, yes. How much? It's hard to say and there are many factors that contribute to the economy and spark timing at WOT is critical to making maximum power, not efficiency. So using 87 octane in the TL will almost always result in reduced performance due to the KS.

Also, gasolines are seasonally adjusted, meaning they have higher volatility (vaporize easier) in the winter and lower volatility in the summer. Government mandates to improve air quality have resulted in significant changes to gasolines, such as the mandatory use of oxygenates (ethanol, methyl tertiary butyl ether (MTBE), and others) in the winter or the reduction of Reid Vapor Pressure (RVP) in the summer. The addition of oxygenates (especially ethanol) increases volatility while the reduction of RVP reduces volatility.

Gasoline distribution practices often do not allow branded marketers to have much control over their gasoline's volatility other than RVP. Oxygenate (e.g., ethanol, MTBE) use is more dependent on local gasoline markets, rather than specific marketers practice. Therefore, it is difficult to recommend specific brands to avoid volatility related complaints.

I hope this clears things up,

A-Train

 

zzz..... im a mechanic, i know that stuff already

 

excellent write up... i agree whole heartedly too bad most people wont understand or wont care....

 

you may be a mechanic, most people are not.... im glad he took the time to post this

 

Excellent post. Thanks for taking the time to explain, in detail. For those of us that are not mechanics, engineers, or chemists, we appreciate the explanation.

 

This post is uncalled for. If you knew all this already, why have you not posted this information? Too lazy? Don't care enough to teach others? Or what? I am not trying to start an argument, I won't participate, but your post is not needed.

I am done, please continue.....

 

I'm sure your 20 years on this great earth make you a plethara of knowledge.

 

On quite a few forums I visit this guy haroman311 would be booed right off the boards and into the suspended account list.

If you've only come here to say how useless everything is compared to your knowledge, please do it elsewhere.

 

 

This is good in fo bro, keep the info rolling!

 

Great info. I learned quite a few things from it!

 

That was alot to read, but I read it all. Great info, and just for the record, I love the Discovery Channel, Science Channel, National Geographic Channel, and The Learning Channel.

 

Great write up! I learned quite a bit from reading all of it!

 

Great info

 

Nice write up! Good information. That other guy might be a mechanic, but I'm an English major.

It's "accept" not "except", except when you mean otherwise.

 

What about plethora?

 

Good info Atrain. Very well explained. Thanks.

 

I really appreciate brief articles such as this. Although some of the information being disclosed is still over my head, I do take a great deal away from it. Anyways, thanks for taking the time and effort to enlighten the more novice users.

 

Well, it would be a great post IF the facts were all straight (and the poster refrained from using sneering phrases like "if you think otherwise, you're wrong"). After all, who made him the expert at the ripe of age of 28?

There are a number of errors in the post, but two I want to clear up have to do with gasoline behavior in the combustion chamber and the definition of "detonation".

First and foremost, gasoline doesn't provide power in an engine by "exploding" as he says. It does so by burning in a very orderly fashion. If, in fact, it DOES "explode", then you have detonation, or knocking, which are the same thing. Detonation is actually a complex phenomenon, but can best be summed up by saying that it occurs when excessive heat and pressure in the combustion chamber cause the air/fuel mixture left in the cylinder to autoignite late in the combustion cycle (near top-dead-center of piston travel). That causes a pressure spike and a shock wave that reverberates throughout the engine, producing a noise we commonly call a knock or ping. It IS damaging, but it doesn't always destroy the spark plug as stated. Otherwise, the landscape would be littered with broken-down cars, since engine knocking is not an uncommon thing.

The poster also says that "heptane is gasoline". Actually, gasoline is a blend of paraffins (alkanes), naphthenes (cycloalkanes), aromatics and olefins (alkenes). Heptane is one of the alkanes, but only one, and nobody at a refinery would call heptane "gasoline". At least the poster went on to say that heptane makes up only a small percentage of pump gas. And that's a good thing, since heptane is a form of methane and isn't usable as a motor fuel because it tends to explode.

There are some good points in the post, but it doesn't clear up the confusion about the octane rating of gasoline to be used in the TL. The Owner's Manual does that ... use the fuel recommended by Acura, since the engine is designed for that fuel. While it can handle lower-octane gas, it will do so only at the risk of knocking, and knocking (detonation) can result in serious engine damage. Period. Nothing more needs to be said! (And if you think otherwise, you're wrong. LOL!)

 

 

At least give credit to the source. Almost word for word:
http://science.howstuffworks.com/gasoline3.htm

 

Some of you guys are entirely too critical.....

Can someone tell me how to make my ext mirrors tilt while in reverse.........?

 

This info has been posted countless times but people still think that the higher the octane the better the gas. I also get a chuckle when people think that a gas from one manufacuturer is better than another. Gas is Gas! My father worked in the oil industry for over 20 years and if you only knew how much money people waste on perceived "better fuel" is hilarious.

 

only thing i didn't get was hypereutectic, but after googling it, I understand what that type of piston is. The only case I could think of where higher octane comes with better gas is V-power, although they could also make 87 v-power. THe other chemicals don't have to do with the octane level.

 

Chile gives me gas , if its high octane or low it still stinks!

 

Is this a joke? I seem to have a hard time detecting others' synecism

If you are not kidding, it is off topic, but there are 3 position on the mirror switch (left, off, right) that set which mirror to adjust. This same switch triggers the mirror tilt (left - driver's side tilt, center - none, right - pass side tilt)

Cheers

 

Are you referring to where it tilts down so you can see the curb... so you wont curb rash your wheels...?

 

What about it? You mean in excess, or is it access..... *WARNING* lame joke.

 

Yes :-), Just thought I would throw in a little humor stemming from another recent thread involving the mirrors.

Thanks though for the nice reply (you to kensukikatayo). Figured those who didn't "get" my humor would go off on a "hijacking" tangent etc.

"Nothing better than the smell of 114 octane - at the exhaust that is..."

Cheers

 

Good Info ATrain!
With all this said ATrain, what octane do you feed your TL?
87, 89, 91, 93, 94??

 

Yeah, there's a lot of confusion there, too. Gas IS gas, but the things added to it can make one gasoline more desirable than another. Gasoline leaves certain deposits when it burns, and some of the additives actually do help clean them up or reduce them. So in that regard, one brand may actually BE a little better for your engine than another.

And higher octane gas is "better" only if your engine needs it. That is, high-octane gas is better for your engine than low-octane gas if it is designed to run on high-octane gas. In that respect, you could say higher-octane gas is "better" since it burns in a more controlled manner under high compression, high temperature conditions.

 

very good write up, although i already howstuffworked it, i actually still did learn more by reading. So, how do we know when to use higher octane? the TLs have have 11:1 compression I think its safe to say we should use higher octane for the highest performance. But lets say in a 2004 toyota corolla? It is of course not necessary, but would it help even the slightest bit??

 

so what would you guys like to know? ask away, and ill tell, feel free

 

what u guys wanna know? u can test out octane any way. wanna know something? shell V power gas is horrible, dont buy it, cuz they added up to i believe 40% alchohol, and guess what too alchohol is bad for injectors, basically your whole fuel system. u can use a RVP test to test out the octane/pressure of your fuel. cats can acutally speed up air flow , so keep your cats, unless you run leaded fuel, then dont, cuz your cats would be ruined. coil over plug systems create atleast 2 times better burn then a tradition distributer type system. if u really wanna F somebody up, what u do is, if they have a distributer, take off a spark plug, and use a pencil, and make a line from the post on the distributer, and run a pencil mark all the way down the cap. they will be missfiring if u guys wanna know anything, just send me a message or ask on here, ill help out in away i can

 

and that 14.7 to 1 and u said 14. 6 somethign to 1, thought u are correct, if u hook up any type of gas exhuast analyzer machine to a vehicle, or any type of scan tool, and your car is running perfectly efficiently, all the machines will show it as 14.7 air to 1 part fuel.