i was wondering if using high octane gas in older cars actually hurt the car.....i have a 91 and wondering if a high octane gas would hurt performance of the truck or would it be better for it

try searching this subject. if i remember correctly it isnt good to run high octane gas in your truck all the time. it is good to run it once in awhile though to clean things out. this is for a stock truck. if you have a chip and depending on the programing of it then high octane may be ok.

OK, OCTANE 101.....

Here's a couple tid-bits

Some people call 87 octane "CHEAP" gas. They're right in regards to the price verses the other grades. However, it's not "CHEAP" in regards to the job it has to do.

The higher the octane the higher the "FLASH" point meaning the harder it is for the fuel to ignite. The lower the octane, the more volitile it becomes. Most all vehicles are designed to run on 87 octane because they all have a low compression ratio which means you need a bigger faster flame front to occur in the cylinder. The higher the compression ration, or the more timing advance beyond factory setting, then the higher the octane one needs to go to eliminate the "PING" monster (pre-ignition).

If you run high octane in a non modified vehicle, the normal outcone is less power and less MPG due to the slower burn rate of the fuel. This is due to the occurance of "DELAYED BURN" causing a slow flame front to occur in the cylinder. Some people will claim that they get more HP and MPG running a higher than needed octane "NOT". If I just spend .20+ more per gallon, I would have to justify it somehow, thus I would tell myself that it's instant power and MPG. it just doesn't work that way.

If you have a stock engine and it is pinging all the time and goes away with the use of a higher octane, then you need to fix the problem that exists. Either a timing issue, lean mix, vacuum leak, carbon build up in the piston area affecting the "SQUISH" zone and so on. A light/smild pinging under a load such as climing a hill before a downshift is normal and just means that the engine is running at optimum efficiency.

It's not even needed to clean the fuel system out as all of the fuels today have detergents in them (mandated by the EPA seveal years ago) to keep the injectors clean from varnish build up.

And the winter time makes it even worse. I don't know how many times that I've helped people get their vehicles started because they were running "SUPER UNLEADED" when it wasn't required. The darn things just don't like to fire.

Hope this helps somewhat.:)

Wow, that explanation should be stickied!

wow thanks thats a great expectation i didn't think that it help i thought that it would hurt the car but people have been telling me that its better for performance

Made sticky so more people will see it..

This was a good/simple explanation of octane...

~Mark

http://www.sunocoinc.com/market/transportation_fuels.htm#GASOLINE

http://science.howstuffworks.com/gasoline.htm

Here is a couple of more of my own tidbits… I have always felt this way and did quite a bit of reading on the topic of fuels. Unfortunately I have not found any well designed tests with data proving anything.

The octane rating describes the fuels properties to resist detonation and pre-ignition. That is it. The other fuel properties are related to the entire blend of the fuel, not the octane rating solely. Higher octane fuels DO NOT necessarily contain less energy or burn slower. I assume it is easy to guess incorrectly because if one were to add dense aromatics to the fuel in order to raise the octane you “could” lower the energy per unit of the fuel. Fact is there are 87 octane fuels containing higher BTU’s per unit than 93 octane fuels and vice versa.

The Flash Point for gasoline is <-40 [F or C as they are the same at that temp]. If you go to this link which contains the MSDS sheets for certain fuels you will see that most fuels have the same flash point listed for their regular, mid-grade and premium fuels.

http://hazard.com/msds/gn.cgi?query=gasoline

Even if the flash point varied, a good spark plug being fired by a healthy ignition system is not going to have any problem igniting the a/f mixture regardless of it being 87 or 93 octane. Besides, gasoline is blended differently depending upon geographical location and season. The Reid Vapor Pressure of the fuel is the property that would have the consequences of hard starting or vapor lock if the temperature and RVP were not compatible. Seriously, think about it. If high octane fuel was blended in a way where it made cold weather starts difficult it would inconvenience all who own vehicles that require high octane fuel. I doubt that is the case.

Originally posted by SWLathrop
[B]The higher the octane the higher the "FLASH" point meaning the harder it is for the fuel to ignite. The lower the octane, the more volitile it becomes. Most all vehicles are designed to run on 87 octane because they all have a low compression ratio which means you need a bigger faster flame front to occur in the cylinder. The higher the compression ration, or the more timing advance beyond factory setting, then the higher the octane one needs to go to eliminate the "PING" monster (pre-ignition).

Harder for the fuel to ignite in what circumstance? I would agree if were discussing a welding crew in the vicinity of fuel. As far as your “healthy” ignition system goes there should be no noticeably differences igniting 87 or 93. The engines in question have low compression ratio’s because the are low horsepower engines with long term reliability in mind. Advanced timing at lower rpm’s requires higher octane fuel because there is more time for detonation to occur as the a/f mixture is ignited earlier. I will agree that different fuel will have different ignition timing points that are optimal but it is dependant on many variables, not just the octane of the fuel.

And the winter time makes it even worse. I don't know how many times that I've helped people get their vehicles started because they were running "SUPER UNLEADED" when it wasn't required. The darn things just don't like to fire.

I disagree with this statement the most. Seasonal blends of fuel are made by the manufactures. If someone is experiencing cold weather starting issues it is related to something other that the fuel octane ran.
In closing I run 87 in my ‘X’ but only purchase gas from companies such as Chveron, Shell, Exxon-Mobil, etc…. I do not buy gas from ‘Mr. Gas’ or ‘Gas City.’
You should all read the book High Performance Fuels and Fluids. It is very informative. Unfortunately, nothing will convince me 100% until I see data from a well set up test.

Has there been a poll in the "poll forum" about fuel octane?

This is a complicated subject.

Compression: higher the compression the higher the octane
In actuality as your veh gets older your compression lowers, due to wear etc.
So lower octane as your veh ages if anything.

I don't want to burst anybodys bubble, but 90% of the gasoline sold in America is supplied by common carrier pipelines. That means that gasoline is gasoline. The Exon, Shell and mom and pop stores get their gasoline from the same source.

it is but then the companies add there indivual additives to them

True! That was a question on some show that I saw a while back! The question was: How can it be that one ship delivers ALL the gasoline to Hawaii but there are different brands of gasoline sold there? The answer was that the companies add their own additives to make up their own brand of gasoline!

Yea sure they do. The additives leave the refinery with the gasoline.

Originally posted by NoLimit4E
i was wondering if using high octane gas in older cars actually hurt the car.....i have a 91 and wondering if a high octane gas would hurt performance of the truck or would it be better for it

I have run High Octane in a '91 and '96 all of the time with no ill affects. I believe Higher Octane does give more power. I've experienced this as well as been told this. The higher Octane burns slower and longer giving better kick to the pistons creating more power. Back when leaded fuel was still used the minium octane was about 103, or somewhere around there, much higher than todays fuel anyway. Also Higher octane will burn a little cooler which is better for the engine.

Ok, go ahead and clog your injectors, foul your plugs, cats, and O2 sensors, and carbon your intake tract.

Just run some injector cleaner through every once in a while like you should anyway and you'll be fine. Like I said I've been doing this for years, and don't run injector cleaner through that often with no problems.

Originally posted by briwayjones
I have run High Octane in a '91 and '96 all of the time with no ill affects. I believe Higher Octane does give more power. I've experienced this as well as been told this. The higher Octane burns slower and longer giving better kick to the pistons creating more power. Back when leaded fuel was still used the minium octane was about 103, or somewhere around there, much higher than todays fuel anyway. Also Higher octane will burn a little cooler which is better for the engine.

the flame speed of the fuel is not effected by octane.

you want peak cylinder pressure to occur ~ 15 after TDC. that being stated the only advantage of a premium fuel over regular would be if the optimum ignition timing for the regular fuel to create peak cylinder pressure resulted in "knock" or "detonation"

anyway, if you ass dyno can feel the power difference between 87 and 93 [which is not there unless you were experiencing knock] you should quite your job and and become a tuner... :rolleyes:

You have an automatic Explorer don't you? It takes a significant power increase to notice a difference in a vehicle with an automatic transmission due to the slipping in the transmission. I have a manual Explorer where minute power differences are much more noticable.

I disagree, I believe the flame speed is affected by Octane, that's what higher Octane fuel is, and the purpose of it, slower burning, that is one way it prevents knock.

I don't want to burst anybodys bubble, but 90% of the gasoline sold in America is supplied by common carrier pipelines. That means that gasoline is gasoline. The Exon, Shell and mom and pop stores get their gasoline from the same source.

This is DEAD wrong. Exxon sells nothing but Exxon Gas, Shell sells nothing but Shell Gas, Chevron sells nothing but Chevron Gas. Aka, Exxon Refinery - Baytown Texas. Shell Refinery - Deer Park, Texas and so on.

Where did you get your facts? I know the "true difference" in ALL gasolines. I have sit in the labs watching the lab techs run RVP's, distallations, etc. I have been surveying Gasolines now for 20+ years. Where does the gas go that Valero Refinery makes? I will tell you, that gas along with off spec gasoline goes to the Mom & Pops. That is why there gasoline is "Cheaper". End of discussion....

HotDogs, gasoline sniffer and tester!!!

One of my dad's patients works for the dept. of Agriculture, is that where you work?

Anyway, this guy said that half the time they test "Racetrac" brand gas it tests about the same as kerosene :rolleyes:

I use Exxon, Texaco, Shell, or Chevron. Fords tend to like Texaco and Chevron, while my VW likes Shell and Exxon.

Thanks Alec, I work for inspection companies that are hired as the "middle man" between buyers and sellers and also help protect the consumer against bad gas. We do all sorts of "testing" on gasolines, rather it is transferred by rail, barge, ship, pipeline, or by truck. Gasoline is only manufactured at Refineries period. It is NOT "all the same". It may or may not have the same analysis ran on it, but they pay big money for those tests to be ran. It is my job to make sure that those samples of gasoline to be tested are pulled and stored correctly according to the standards set up by the US Government, Aka, API Chapers. API = American Petroleum Institute. I can site these chapters by heart, and have had to do it many times arguing over valed points raised by the "sellers and buyers". If a multi million dollar deal falls, guess who has to answer the questions that are sure to follow. Where did you get your samples? What type of samples are those? Did you ice down those RVP samples BEFORE they were tested? And on and on. RVP = Reid Vapor Pressure, this insures that the gasoline will be sold in the "right" territory, Aka North, South, East, or West. Not forgetting the mids either. All regions have different specs for gasolines. These refineries MUST meet those specs before they can sell this gasoline to them. It is blended to meet those regions specs. The only things similar in gasoline all over is that it will burn and it stinks. LOL.

As a matter of fact, I beleive it was a company called Saybolt that went down for falsifing records on reformulated gasolines in the Northern region. The EPA standards are there for a reason, so Johnny comsumer who doesn't know the difference between 87 octane and 101 octane, except that the numbers are different and one cost allot more than the other is protected.

The US also sells allot of it's gasolines to other countries in exchange for Crude oil. We do allot of trading with PMI of Mexico for it's crude oil in exchange for finished gasoline. Notice that cars in Mexico run different than the cars in the US? LOL, I know why!!!

HotDogs

I don't know about where you live but here in CA we have refineries that don't have they're own stations. We also have Valero stations, and refineriies, and I believe they're a national chain. Just because you don't have them in you area doesn't mean they're a mom and pop operation. Also, the price of gas is more expensive at big names for a number of reasons. Not necessarily that their fuel has a better formulation. For one, they advertise nationally. Millions and millions of dollars spent making people think they're gas is better. And second they are feeding people the line that they're gas is better so to prove that they charge a little more. Giving the illusion that it's a premium product. Gas stations get a call (or they used to when I worked there 14 years ago) from the head office which sets the price at a station.
I guess the short answer for me is do what makes you feel best. And don't believe the hype. Unless you want too :D

BTW- how do cars in Mexico run different?

I don't know about where you live but here in CA we have refineries that don't have they're own stations. We also have Valero stations, and refineriies, and I believe they're a national chain. Just because you don't have them in you area doesn't mean they're a mom and pop operation. Also, the price of gas is more expensive at big names for a number of reasons. Not necessarily that their fuel has a better formulation. For one, they advertise nationally. Millions and millions of dollars spent making people think they're gas is better. And second they are feeding people the line that they're gas is better so to prove that they charge a little more. Giving the illusion that it's a premium product. Gas stations get a call (or they used to when I worked there 14 years ago) from the head office which sets the price at a station.

Prices are set by costs. I live in Tx. Any since you live in Ca, you should know about the higher standards of gasoline as apposed to people that do not live in a Smog town. Reformulated gasolines cost more. Period! Not everyone sells a Reformulated Gasoline nor do some refineries make reformulated gasolines. Reformulated Gasolines are the cream of the crop. They pass ALL tests with flying colors. (if that makes since) They are harder to get passed than, just plain old gas at Mom & Pops. The testing and retesting that these gasolines go through to ensure the public that they are getting what they pay for must be passed on. To run analysis on 1 tank of gasoline after it is manufactured, before it is sold, costs over 2k, a small price to know what is in that tank I might add, plus O/T for the tech, all of the analysis can not be ran in an 8 hour day. Plus the costs of me or someone like me to go bust off on that 60 foot tank. It use to be easier 15 years and 100 pounds ago, LOL. But knowledge costs you.

You are the public, don't you want to know that what you buy is what you are getting? Don't you want to know if additives have been put into gasoline to make it "on spec"? Don't you want to know that the major refineries can make mistakes and what happens when they do?

HotDogs

Originally posted by unclemeat
I don't want to burst anybodys bubble, but 90% of the gasoline sold in America is supplied by common carrier pipelines. That means that gasoline is gasoline. The Exon, Shell and mom and pop stores get their gasoline from the same source. I don't want to burst your bubble.... wait, yes I do.
Yes, most petroleum products are carried by common carrier pipeline at some point.
And no that doesn't mean gasoline is gasoline.
It's called batching.
Through scheduling and proper use of spacing mixtures the same oil lines carry regular gas, premium gas, diesel, kerosene, av gas, jet fuel, anhydrous ammonia and other liquids.

Just because all the trucks in an area go to one supply station, and there is only one pipe coming in, does not mean they all get the same base gas.


That being said, yes in some areas the name on the station isn't the name on the base gas.
Take Hawaii for example.
Remember that one boat mentioned before?
It doesn't even carry gasoline, it carries crude oil.
That oil is then sent to either the Teroso refinery or the Cheveron refinery.
Shell, Texaco and the others then buy gas from those two refineries that meet their own specs to be shipped to the stations and mixed with their own additives.

Well, they usually don't even buy it.
Instead they have worked out exchange programs.
Cheveron makes 100,000 gallons of gas for Shell in Hawaii and then Shell makes 100,000 gallons for Cheveron in an area that Cheveron needs it.
Either because the Cheveron refinery that supplies that area couldn't handle the current load, or they just don't have one.

Well, some very good information here. I used to study chemistry, and I remember this subject did come up briefly, about octane cracking and such...but I forget it all now. Anyway, just to add my own situation, what I have observed is that when I use octane 92, it is a very noticeable change. It's like I have a very fast engine...the acceleration seems very noticeable, and the increase is dramatic, giving me the impression that I have a different engine or vehicle even. When I use octane 87, I usually have pinging if I even make a very slight acceleration. I find that in colder weather it runs better, but in hot weather, I really have bad pinging some times. Whether hot or cold, the pinging is very much reduced with the higher octane fuel, and the engine purrs so smoothly & quietly; octane 87 seems to chug very sluggishly like I'm pulling a trailer up a hill. I have a 98 Explorer, 31" tires on it.

Compression: higher the compression the higher the octane.
Not true. It all depends on how the engine disipates heat and the shape/size of your combustion chamber. An innefficiant combustion chamber can cause minute hot spots in the compressed gas. That combined with hot valves, head, pistons ect. might be the breaking point, causing pre-detination. Eliminating either will drastically help performance, but todays engines are built for longevity, not performance.

For example, my bike has an 11.8:1 compression and 55º (stock) of advance. (Aluminum everything and a magnesium valve cover to boot). Owners manual calls for 87oct. I'm getting close to 3rwhp/CID

I find that in colder weather it runs better, but in hot weather, I really have bad pinging some times.
Can you get a 160º thermostat? Reducing the engines temp will help out
Whether hot or cold, the pinging is very much reduced with the higher octane fuel, and the engine purrs so smoothly & quietly; octane 87 seems to chug very sluggishly like I'm pulling a trailer up a hill. I have a 98 Explorer, 31" tires on it.
Your knock sensors are going off, retarding your timing. That is reducing your power.

I thought that a higher octane does have a (VERY VERY) slightly lower BTU content.

The only way running higher octane in a lower octane
setup motor is if you advance the ign timing to the edge
of spark knock under your heaviest motor load and then slightly back it off!
Just to the point that you aren't experiencing retard under
that load.
Improvement minimal.

Then the first time some hot day under load when you don't put that high priced fuel in its going to pull all that
timing out and run even worse. :(

later
jaykar

I used to work for a reiner and marketer of gas.

All gas is the same at the terminal where the delivery trucks are loaded up. Additives such as techron are added at the terminal. Usually into a tank that is earmarked for each company.

All the gas in Arizona comes from 2 pipelines. Several refieries pump gas into that pipeline. It is shipped to the terminal (tank farm) in the phoenix area. At the tank farm, additives are added (if needed).

Now, other than the additives, all gas is the same in every station in arizona.

Where you have to be careful, is the actual station. Certain companies keep their tanks and fueling equipment in better shape than others. A mom and pop station might not be able to keep up the same maintennance schedual as the major retailers. This can cause rust, water, or other contaminents to enter the fuel supply. These contaminants can cause damage to your engine.

I generally use Chevron, as they are up there as one of the best fuels available. Its that darn techron stuff. And no, the company I worked for was not Chevron.

I have run High Octane in a '91 and '96 all of the time with no ill affects. I believe Higher Octane does give more power. I've experienced this as well as been told this. The higher Octane burns slower and longer giving better kick to the pistons creating more power. Back when leaded fuel was still used the minium octane was about 103, or somewhere around there, much higher than todays fuel anyway. Also Higher octane will burn a little cooler which is better for the engine.

I have to disagree with this comment.
The minimum octane back in the day was the same as it is today. There was never a pump gas that was rated at 103 octane. Sunoco 260 was rated way below 100 octane.

umm Rayco, you can go to alot of gas stations in the nicer areas of charlotte, NC and they have unleaded 103 racing gas, if you live there look off the ballantyne exit on the beltway, first station on the right by the hotel. there is DEFINITELY 103 octane pump gas, was almost 3 bucks a gallon last year, now I never bought it, but I did only put 89 or 91 octane depending on when payday was in my '00 impala Ls. and it did run better on 91 than 87, couldn't tell you about perfo, but the idles were better and it didn't ping, and there was nothing wrong with the motor, but since new it always liked the better stuff. my explorer usually runs fine on 87 oct, when it doesn't, I top it off with 91 at about a third of a tank and it stops pinging.. I usually associate it to bad gas, it happens.

I don't know what the compression was, but I can tell you from experience there are times you can definitely tell when you have good gas, but I would associate it more with the facts that A. you let your tank run tooo dry. or B. you got crappy gas the last time, by buying it right after they filled the station tanks, or because the shop had water in the tanks, on purpose or not. or C. You need a tune-up...

there is currently a 103 pump gas, sold very recently at least, (who knows since gas prices shot up though) maybe not in NJ, but it does exist.

I thought that a higher octane does have a (VERY VERY) slightly lower BTU content.

Strictly speaking, this is both true and false. Sans additives that the particular station may add, gasoline is comprised primarily of hexane, heptane and octane. As the prefixes suggest, hexane is comprised of six carbon links, heptane of seven and octane has eight.

When you measure energy per volume, you'll find that:


Name Formula Boiling Density Energy Density
Point g/mL @ 15C MJ/kg MJ/L
Hexane C6H14 68.7 0.663 44.73 29.66
Heptane C7H16 98.4 0.688 44.57 30.66
Octane C8H18 126 0.706 44.43 31.37


So, as you can see, hexane and heptane are less dense than octane, so if you measure energy per mass, they contain more energy. Conversely, if you measure energy per volume (since volume is how you buy gasoline), you can see that Hexane and Heptane have approximately 5.5% and 2.3% less energy per volume than octane.

So per gallon, fuel with more octane would contain more energy, if gasoline were only comprised of these three molecules. That is not the case though. Different companies add different things to their mixes. All companies add detergents, etc.

Personally? I use the lowest octane fuel that I can in a vehicle that doesn't produce ping. In my jeep, that's 87 octane. Since I replaced the heads in the Explorer (decreasing cylinder volume, increasing compression) I have to use 91 octane in it.

(fyi, since I don't memorize chemical trivia, I looked those numbers up at http://www.chevron.com/prodserv/fuels/bulletin/aviationfuel/B_about_hydrocarbons.shtm which happened to be the first place I found them when I googled it :)