Definitive data on fuel brands anyone?..

Here in CT we have 93 octane as premium. Couple of questions. Does anyone have links to good reading on whether say Sunoco is better than Getty or a truck stop's brand x. Really wonder how much difference is out there on this stuff. Also, what benefits (or damage) can occur from running 100 octane vs 93. Thanks.

A research company here in Texas test fuels and I have spoke to one of the gentlemen who does the test and asked him what is the best company for fuels. I know you live in CT but for us guys in Texas, it is Texaco, second Chevron, and then Exxon. He told me what they test for mostly is how uniform the samples deliver the octane rating. The poorer brands fluctuate a lot. Sunoco has always been a brand that is respected and I believe as long as you dont run leaded fuel, it should be fine in our cars.

http://www.toptiergas.com/ Generally all the gas comes from the same place and the difference is in the additives that supplement the base stock. Depending on the prices in your area sometimes it's cheaper to buy top tier gas, other times it's cheaper to less expensive gas and buy additives seperately. In SC it was a break even so I went with Shell. In MA I go with Sunoco and add Techron additive on a regular basis since the Sunoco station is ~$0.15/gallon cheaper. In regards to octane, the minimum octane you should run is listed by the manufacturer 93 for the 996. Octane determines the knock threshold of the gasoline and higher octane offers better resistance to detonation. With high compression engines the higher octane is necessary to avoid detonation. Modern engine computers measure knock and reduce your ignition timing to avoid detonation. So if you use gas with lower octane your computer will notice and retard your timing to avoid damage at the expense of power. Depending on the software, so computers will allow you to take advantage of higher octane fuel by advancing the timing and producing slightly more power. I don't know enough about the P-car engine management to answer whether there is an advantage for us. S.

Sorry, Tippy, but don't buy the "fluctuating octane" rating BS. I almost blew tea out through my nose when I read that one. Pretty funny. The post above is absolutely correct. All fuel comes out of the same pipeline. The ONLY difference is the additive package.

Here in California we use 91 Octane for every fill up ... throughout the life of the car (mostly). Is there evidence that this is bad?

Check your owner's manual, but if I remember correctly, Porsche recommends 93 octane and sets a minimum of 90.

the harm of 100 octane is $8.00 a gallon.

Get mine for 5.59...still painful.

Not bad. Just that your car will "de-tune" itself to protect from the lower octane rating.

WOW, do they give you a "reach around" or at least a kiss every time you fill up (or get filled up)?

I'd be wanting more than that for that price! (You are too funny!) BTW, can I have a graphic of that image? Maybe not.

so how can I up the octane in CA??

...maybe additives like this. http://www.stp.com/fuel_oct_boost.html I've no clue if they work, but there are plenty of them around. Here's an article from cars.com http://www.cars.com/carsapp/national...odaysgas1.tmpl ...not glowingly endorsed. So what octane rating is premium in CA?

in Cali? It is crappy @ss 91. We got the same crappy Cali gas in Nevada.

Wow! I'm shocked. I guess I never noticed the difference between there and the east coast when we moved.

You ain't kidding! I was less than happy when I moved from DC out to Vegas for 4 years. Talk about crappy gas. That west coast Cali crap is for the birds. Thank God I am back in the south where we have the good stuff.

Typical. Should not be surprised though... Typical California. cost more, less filling.

Uh...I didnt make this up, the guy worked for a research company and he not into cars. I dont know why he would be making this up. Are you an expert and explain this better and tell me why I was misinformed?

Still looking for definitive research on fuel quality and what high octane does to our car. Enjoying the opinions so far though. thought guys would have links to this stuff. I will start online research.

I thought the posters did a good job of responding to your question, but here's more info that reenfoces some of the points already made: http://vettenet.org/octane.html

Those of you in CA could consider mixing in a small quantity of 100 octane with their 91 to bring the overall level up to 93. Personally I wouldn't be worried about it. As someone else said it's not going to cause any damage, you'll just be slightly down on power. CT03911, I'm not sure what you're looking for...100 octane won't hurt your car, and if the computer is capable of advancing the timing you make pick up a few hp. Alternatively, if you plan on always running higher octane you could have your computer flashed with a new timing map to take advantage of the higher octane.

I am glad I just moved to TX where I can feed my Pcar with 93 now compared to 91 max in CA... So far I have not seen any noticeable differences... at least on the streets. Cheers,

Fuel burns more slowly as the octane number increases. Our cars' DME systems adjust ignition timing to avoid pre-ignition - that pinging sound you sometimes hear under acceleration. The goal of proper ignition timing is to have the flame front in the combustion chamber fully burnt at or just after piston top dead center (TDC). If the fuel charge is completely burnt prior to TDC the result is termed detonation, imagine the top of the piston whacked with a hammer. This harms numerous internal engine components and, if taken to the extreme, will result in a hole in the piston crown, damaged crankshaft and rod bearings, cracked cylinder heads, slipped cylinder sleeves, etc. Retarded ignition timing results in lower power and wasted fuel - the charge is still burning after TDC. To sumarize - advancing ignition timing up to but not including the point of but not including pre-ignition equals more power, retarded ignition timing equals poor performance and poor fuel economy. Running higher octane fuel in our cars allows the DME, within its' compensation adjustment limits, to advance ignition timing and create more power.

I didn't mean to imply anything about you, please don't take my post that way, but as I said, what you were told is plain and simply wrong. I'm a research scientist. I know chemicals very very well, as it's all I do every day. Just because the guy worked for a "research company" does not necessarily make him a "researcher" in the scientific sense. In the loosest sense it means that he looks things up in books and writes a report on it. Here's a link to a DOE web page explaining the US gasoline network. http://www.eia.doe.gov/neic/brochure/gas04/gasoline.htm I'll draw your attention to the section that is titled "From Refinery to Consumer" This link http://www.aaanewsroom.net/Assets/Fi...stribution.pdf Shows the US gasoline pipeline network. I repeat - all gas in a region comes out of the same pipe and then has an additive package added to it. I am fortunate enough to work for a company that used to have an oil additives business (before we sold it) and know enoguh to be dangerous, even though this is not my specialty. I was not around when that business was part of the company - I was just lucky enough to work with some smart guys who know this stuff really well. Despite the creative marketing of gasoline companies they are loathed to admit that the only difference between their gas and the Costco down the street is the additive package that goes into the fuel in ppm levels - i.e. it does next to nothing. Whether you buy from Texaco or Costco makes no difference, as all fuel must conform to Federal standards on burn rate, emissions and detergency (i.e engine residues). In the end it's all smoke and mirrors. Save your money and buy from Costco, as you're getting the same product, but without paying for the marketing. You will also find links to this on the DOE website. I'd be happy to answer any other questions you might have.

I use Sunoco Ultra 93 octane. Runs fine - around $2.49/gal in PA currently. Phil

BTW, one more myth to bust. In a non-Porsche, when they say change your oil every 3000 miles, that's bogus too. You're good until 5000 to 7500 miles, depending on your use. Most oils have little contamination below that level, so changing your oil does little but enrich your dealer when you pay them to change it.

I totally agree with you on this one, my friends wife wont budge on the 3000 mile oil change and she runs Mobil 1 in her Lexus IS. Awesome, now that I know you are a research scientist, why does everytime I use a "Costco" brand of fuel, my car gets consistently less MPG per tank? This is a huge reason why I use the "better" brands. My '95 vette would get about 60 miles per tank less everytime I used a "lesser" brand. It was more cost effective to pay up front the extra 2-4 cents per gallon. By the way, the "research" company the person worked for, I am pretty sure you have to be an engineer to work for them from what my friend has told me (who is an engineer). The company is well known in our city.

Well, there are many reasons why you would get less miles per tank. The fuel (mostly) is not one of them. Chemically the fuel is pretty much identical. When I said ppm of additives, I meant it. That means that around >99.9% of your fuel is the same regardless of the source. This is not a great enough variation to change your gas milage. The additives package typically consists of surfactants to go beyond regulations and other minor stuff like that, but nothing that will dramatically change how your car runs. Reasons that come to mind (and there are probably more) are as follows: 1) Winter vs. Summer formulation. I consistently get lower milage in winter. 2) Weather/Temperature - similar to above, but you can get cold weather on a summer formulation 3) Driving style - this is huge! 4) Driving type - highway vs. non-highway - again, this is huge. I've had my cars vary by as much as 10mpg on the same source of fuel in the same car. Additionally, I've had fuel economy change in driving from one region to another. I'm not winding you up here, you can do a search on this and come to your own conclusions, but the source of your fuel has little impact on much other than your wallet. Octane rating is the only thing that you should care about, as the govenment takes care of the rest in terms of formulation requirements and ensuring that your engine stays clean. Oil companies have a huge amount invested in keeping you thinking that your brand of fuel matters, when in fact it does not. Brand loyalty is worth more to them than anything else.

Another thought here - how big is your tank? Assuming a 12 gallon tank that's a difference of 5 mpg, that could easily be caused by the factors I listed.

a good article on gasoline. What the writers found is basically buy a name brand gasoline from a busy station to avoid getting stale gasoline. The higher grades go off pretty quick. There were some differences not only between brands, but between different samples of the same brand. But most often, the difference was attributed to how fresh the gasoline was or was not. Discount brands sell the same gasoline, but with a reduced additive package. Using these lower additive package gasolines can result in engine deposits and reduced performance over time. Octane variations can occur though most problems are with quantity, not quality. One of the USA car mags just in the last couple of months did an article on gasoline checking in Mich. which I think it probably representative of the country at large, at least in the number of stations that will be or would be found wanting... The number was a hundred or so out of maybe 5000 stations checked. Gasoline is shipped via pipelines and these pipelines can carry a variety of other fluids. In the case of transporting gasoline, 87 octane gas is loaded into the pipeline first, followed by 91 octane gasoline, followed by another slug of 87 gas. Surprisingly, the gas does not mix much during transfer. At the destination, the 1st bit of gas is removed and used on site for power/heat. Then the portion of the 87 that is uncontaminated is removed. It may contain some mix of a portion of the 91 octane gas. Then the slug of 91 gas is removed and the removal is guaged to remove only the uncontaminated portion, uncontaminated with any 87 octane gasoline. The 2nd slug of 87 gas is removed. (Ethanol can't be shipped by pipeline because they contain water which the ethanol will pickup.) Anyhow, if the pipeline company is overly agressive with where it decides the portions begin/end it can pull some mildly contaminated 91 octane gasoline in with the uncontaminated 91 octane gasoline so there is some reduction in quality and octane rating. If the company errs the other way, the 87 octane gasoline ends up with some 91 octane in with it. (Mid-grades are "created" at the station by the mixing of 97 and 91 octane gasolines.) Overall, though, I think things tend to be handled well. I'm sure if there's some contamination beyond some reasonable amount, the pipeline company could be in for it... Still, your best protection is to buy from a busy name brand gasoline station. Sincerely, Macster.

Forgot to touch upon this. Running the proper grade of gasoline allows the engine controller to maintain sufficient ignition advance to extract the maximum amount of power from the burning of the gasoline. While the engine controller can sense incipient knock/detonation, and retard the ignition timing, thus saving the engine from destruction, it is not an ideal situation. In fact, it should be looked upon as simply the lesser of two evils. Performance and fuel mileage will suffer. Enough so that one finds what he saves on gasoline at fillup is eaten up by having to fill up more often. IOWs, you end up burning more of the cheaper gas for a net gain of nothing. Plus, or worse, because of the retarded igition timing, the fuel starts burning later in the power stroke and this results in exhaust gas temperatures being higher. Thus everything from the combustion chamber is subjected to a higher heat load. Many think that octane matters only under full throttle but full throttle is a piece of cake, cause the engine controller can and does go open loop, thus it can ignore emissions and enrichen the mixture to provide protection against detonation without having to retard ignition timing. It is those part throttle moderate loads to moderately hard loads that really cause problems. The engine controller must mind emissions so it can't go richer, so it retards ignition. Not good. Running a high performance engine on gasoline below its recommended grade of gasoline is false economy. In a pinch, not a problem. But for a steady diet.... Sincerely, Macster.

Stale gas, do you really believe that? Gas stations refill their tanks every couple of days - it does not go 'stale' on that sort of cycle. That claim is bogus. I also doubt the claim that higher grade fuel would go 'stale' faster - it's a hydrocarbon - it does not degrade that quickly, unless attacked chemically, or thermally cracked at high temperature. The additive package may change with time, but that would apply to all of the grades equally (assuming the same package used across all the grades of a particular brand). The timeframe for degradation is not days or hours, try several months - not something that can happen in a gas station that has customers, or a car that is getting used. Octane variation is also bogus. All gas within a formulation has to be tested to be within spec. when it is transfered from the pipeline to bulk storage. You can't vary outside an octane range once it becomes a formulated fuel grade, it is what it is sold as... not unless the UK is less stringent on fuel formulations than the US and I doubt that. As I said in my post, the additive package is not relevent in the US. Regulations ensure that the additive package prevents engine fouling and carbon build up. Sure you can go beyond the regulated minimum, but it has little effect, other than a marketing boost. Your comments on octane are otherwise correct. The fact that people buy into the comments in the article just goes to show how effective marketing can be.

Now, one issue we have not gotten into yet is the subject of fuel fraud, i.e. gas stations selling fuel that is not what it is claimed to be - not the franchise brand, or adulterated in some way. This has been an issue in recent years and fuel companies go to great lengths to detect counterfeit fuel and will test for it on each delivery and during random inspections.

You certainly are kidding about this point. Variation exists in everything. Just because the government "certifies" it does not mean much. The measurement systems alone can vary greatly. I have not specifically studied these measurement systems, but have studied FAA and FDA certfied measurment systems for 2 decades and found many to be are entirely incapable (so much for government certifications). Do you know the spec, BTW? All in all though a good discussion.

Sure there's varation, but the question is whether it's significant variation and I would argue not, otherwise it's pointless having a spec. and measuring towards it. I don't know the spec., but I'm sure we cold find out easily enough.

20 Gallon

So, that's basically a 3 mpg difference and within error. I know when I fill up my SUV (a 21 gallon tank) that my milage varies by as much as 4 mph on a regular basis.

It is incorrect to state that: " engine controller can and does go open loop, thus it can ignore emissions and enrichen the mixture to provide protection against detonation without having to retard ignition timing as this is independent for what octane you are running". The ONLY control related to octane at WOT besides the pre determined program are the knock sensors. If you knock, you lose timing and power. There is no change in fuel enrichment regardless of whether you are running 100 octane or 87 at WOT.

Good catch - I'd missed that. With regard to octane specs. A quick Google search reveals that octane ratings are mandated minimums, therefore, you only gain by variation - if it's 91 octane, then it really means that it's 91+ octane. i don't think we can really complain about that kind of variation.

The summary of this thread so far is that there are lot of myths and untruths out there.

Just me being a smart*ss, but we've also learned you are not capable of editing one of your previous posts and so you just keep adding posts? Sorry, just a statisticians sick form of humor (ignore the man behind the curtain).

but simply the engine controller's attempt to meet the required torque demands by the driver. At most other times, the driver's demands are tempered with emissions compliance among other things. (In some cars, torque output is limited to prevent drive train damage.) But at WOT the assumption is -- for now anyhow -- that meeting the driver's demands is paramount, albeit not at the risk of letting the engine detonate itself to pieces. At WOT (or at some point a bit below that) the engine controller can and does go open loop and enrichens the mixture some (not gobs but enough) to provide maximum power. I see this while driving my car while monitoring various engine controller parameters, outputs during various engine operating scenarios. Sure, if knock or incipient detonation is detected the engine controller will still attempt to counter it by retarding ignition, but under wide open throttle ignition advance is not as advanced as it will be at other times, under less severe throttle openings. The engine controller also goes open loop under closed throttle coast downs.... Sincerely, Macster.

The computer does exactly what the program was written to do based on various sensor inputs. It has no idea nor does it care what the driver wants. It is a calculation and will ALWAYS do the same thing if input is equal. If your timing is programmed to be at 26 advanced at WOT under specific temps, air flow, etc, then (everything remaining the same) it will be at that setting whether you run 89 or 93 octane fuel UNLESS the computer receives a signal from a knock sesnor telling it shut down the timing.

Ouch. Justified, but ouch.

I have learned a lot from your posts guys. Excellent links. Sounds to me like there is definately different gases out there sold by different companies but that you cannot be assured that the say exxon gas you are buying is not shells because of economies of shipping vs swapping from competitors. Furthermore most of the base fuel is the same it is the additives we are interested in. Very interesting stuff indeed. I still kind of wonder if one manufacterer has a prefered additive package, especially since all these articles seem to say the additives are expensive. So one would think a cheap brand may not add much compared to a "high end" brand. Wish there was more info on this.

Thanks for all the links guys. Great info. Shell, Chevron and Texaco apparently have the best additive packages for us here in the U.S. It seems I should assume all the base fuels are pretty equal and sometimes your fuel from one retailer may even have originated at anothers pipeline for economic reasons. Wouldn't want the big oil companies to dip into their profits. Thanks for the feedback to all.

I used to think all gas was the same, so I put Safeway gas in my 996. Then it started to sputter between 4k and 5k at WOT in 2nd and 3rd, on that fave piece of new pavement out in the new subdivision... So I started putting Chevron into it and 2 tanks later, the problem was gone. I didn't get too worked up about the Safeway gas, until my wife started complaining about stuttering response in her SUV ('04 Lexus RX330). She is not Rick Mears by a long shot, so for her to notice this was interesting. I drove it a bit, and noticed it as well. I asked her where she got gas. Safeway, 7-Eleven, Costco. Whatever was cheapest. I told her to put Chevron in for a while and report back. By the end of the first tank, she said the problem was solved. I told her to stop buying cheap gas, and now both cars are happier. On a different note, I used to go to a Chevron and fill up my old Tercel. Then it started dying at idle in traffic all the time. Clogged fuel filter. Cheap item. Replaced, problem solved. 3 months later, same thing. New filter, problem solved. The third time though, I was getting irritated. Asked buddy mechanic, he said, go buy gas from a NEW gas station, not that old thing with 20 year old tanks. He said OLD tanks have sludge in them that can foul the filter. After swtiching to the new Shell across the street, we no longer replaced fuel filters 2 and three times a year. It is hard to say what the story is, but in my experienced, gas quality does vary, quite a bit, based on the addititves and the storage tanks. Your mileage may vary...