I recently moved from NJ to Indiana. I always used Mobil gas, but they dont have Mobil gas stations in the Indy area and i had to settle down for BP Amoco. But when i visited Illinois last weekend, i found Mobil Gas stations and the car definitely felt more responsive (noticeable difference in throttle response). This is not the first time i am feeling this. The car just feels peppier everytime i switch back to Mobil and a little sluggish when i drive on other gases. I have even tried Sunoco 94 Octane, but it did not feel like Mobil 93. Can the brand of gas make such a difference or is it just me?. I am so much into this now that i am watching my miles on the G until i can find a reason to go to Illinois!!!

 

Down here in Miami, I've used Mobil 87 in my SR20 for the last 2-3 yrs... I even used a tank or 2 of 93 in my G35 Sedan..that said.. I have switched to Citgo for the last 2 93 fillups... do I notice a difference in gas mileage? The mobil MIGHT be about .5-1MPG more.. but here's the kicker: 93 Mobil costs $2.05 a gallon, Citgo 93 runs $1.90.. so for $.15 cents per gallon saved.. I can justify losing that minimal loss.

2004 G35s 5AT DG/Graphite/Premium/Huper Optik Tint

 

Gas quality in every region and every season varies such a great deal I don't think you ever get the same tank twice. Last I heard from an aviation fuel distribution guy (take that credential whatever it's worth to you) is that Texaco and Shell were the only two that really put any of their own gasoline standards for auto fuel.

In the midwest, there is a greater use of corn in their fuel, and in the summer you've got different contents than you do winter. What you might be feeling are regional or seasonal differences in the fuel, not retail brand name.

2004.5 Coupe/5AT/Ivory/Everything but chin spoiler/Z Tube-Popcharger/Crawford V5 Plenum on the way

 

welcome to Indiana. I'm from Zionsville on the NW side of Indianapolis. I always use Shell Gas and i drive my car pretty hard. But yet i consistently get 400 miles a tank. I do notice a difference in performance from gas to gas. But i just buy a bottle of octane booster to boost my 93 octane to 103!. And the car runs like a bat out of hell.


04 6MT Black on Black
Premium
Aero
Winter
Injen CAI
Unorthodox Pulleys

 

prabhacar... i made the same move! northeast jersey to indianapolis. i use mainly 93 from bp (or shell) and stay away from speedway or bigfoot. indy gas prices are higher than what we're used to, but more reasonable than what some of my chicago friends have been complaining about. welcome to the midwest.

<font color=purple>.g35girl.</font color=purple>

 

Every time I read any sort of technical subject on most car forums, it amazes me how many people make absolute statements, that are wrong, on subjects they know nothing about. There are basically two types of standards for gasolines; the national one, that established the testing method for determining octane ratings and the environmental based standards, that are more regional and effect emission levels vs. things like ambient temperatures. For the most part "gas is gas" except for differences in octane. In many areas of the country, one or two refineries (often owned by companies you've never heard of) supply gas to all of the various branded gas stations as well as the unbranded stations. In a couple of cases (e.g., Shell) the particular brand supplies the additve package that the refinery adds to the gas going to their stations. However, there is little or no difference in company to company additive packages, because only a few companies make the additives. Typically, "super" has the fullest additive package and 87 octane the least. These additives do things like prevent long-term gum build up in the engine and don't effect near-term performance. Now, will the car be faster or run better, the higher the octane? Each car comes from the factory, set up (i.e., the combination of things like compression ratio, spark timing, etc.) for a specific minimum and max. octance. For most engines, which have low compression, they run well on 87 octane, by design. Increasing the octane used will not improve performance or gas mileage and do nothing but waste money. I won't get into the details of what the octane rating means, other than to say that the specific molecular make-up (i.e., straight chain vs. ring molecules) of the gas effects the temperature and pressure at which the air-gas mixture explodes. If you have a relatively high compression, high performance engine, using too low an octance causes the explosion to occur too early in the compression cycle, while the intake valve is still partially open. This means that the edges of the valve overheat and potentially "burn." The pinging or tinkling sound you'd hear is made by the heating and cooling of the valve. For the G sedan and a few other cars, a range of octanes can be used effectively, because the car has a sensor that detects pre-ignition and adjusts the timing of the spark (i.e., plug firing) to prevent pre-ignition. This prevents any damage to the engine, but reduces the engines performance slightly. On the other end of the spectrum, unless you have changed your engine chip, have a programable computer, or changed pistons, etc., going to higher than 91 octane does absolutely nothing for you. There are heavily modified cars out there (e.g., 15 psi turbos with programable computers) that can actually benefit from 101 or higher octane gas. Back in the sixties, I had a '66 427 Vette with 11:1 compression that required103 octane. When I took the car to Texas, where the highest available octane was 101, I had to retard the spark to prevent pre-ignition. BTW, I'm a chemical engineer by education and worked for Exxon in making oil and gasoline additives.

 

Marty,
I love when an actual engineer comes around, and if you have knowledge of what happens after the fuel leaves the engineers I'd love to learn about that as well.

In the aviation world we debate frequently about the diffs between aviation grade fuel and auto fuel, AKA "mogas" and the FAA, local FSDOs, fuel distribution companies etc. have provided information to one or more of us that tell us things that you seem to be disagreeing with. Someone's wrong and I'd love to get to the bottom of it, at least in my mind.

Are you saying there are no "regional differences" in fuel delivered to any different states? Doesn't California have different fuel standards (or content, please don't word-smith me, you get the idea)? Don't certain regions utilize -ohol fuels more than others (gasohol, or whatever it's called)? Aren't there winter and summer differences between fuels? What's an MTMB and tetryahydra blah blah or whatever it is that the California people complian about...or the stuff that some of the Metro areas require be done to their fuel? I hear Denver has different fuel?

Please, enlighten!

2004.5 Coupe/5AT/Ivory/Everything but chin spoiler/Z Tube-Popcharger/Crawford V5 Plenum on the way

 

So are you tell me that using Super is a waste of money for the G other than the potiental long term benefits? Anyone here consistantly using Regular? I don't mind paying extra for the Super if it does good, but if it has no real benefit, it sounds like everyone is getting dooped.

 

<blockquote><font class="small">In reply to:</font><hr>

What's an MTMB and tetryahydra blah blah or whatever it is that the California people complian about...

<hr></blockquote>
MTBE (methyl tertiary butyl ether)
It oxygenates the gas, providing cleaner emissions. It makes the gas more expensive, and reduces fuel economy.

As a side benefit, it can contaminate ground water, and possibly cause cancer.

http://www.epa.gov/mtbe/

<P ID="edit"><FONT class="small"><EM>Edited by Ryoken on 04/29/04 01:46 PM.</EM></FONT></P>

 

Marvinclt - You misunderstood what I was trying to explain. The G35 sedan is capable of using a range of octanes. Inorder to get maximum performance, you should use 91 octance. However, if you don't routinely make "jack rabbit" starts or drive with the car fully loaded, you can get more than sufficient power with either 87 or 89 octane and not harm the engine. You can change octanes from tank to tank, depending on your expected use. If you traveling on a trip throught mid-west i.e.,(flat, constant speeds, etc.) use 87.

 

Catatafish -
Sorry, I can't help with your aviation fuel questions. I did speak about national stds. (octane) vs. local/regional stds. For the most part local/state stds. are environmentally based. California has the worst potential air pollution problems and has therefore has requirements for emission reductions that are the toughest in the country. For performance purposes, the octane std. is the biggest factor and a specific octane will the same performance. Getting into what's done to meet the different emissions (e.g., reformulation, additives, etc.) is much to complex to explain here. The addition of alcohol in somes states is a political/economic issue. The addition of alcohol, for and against, has been argued for years. Winter/summer differences are made for two purposes; mostly to lower emission, but in cold areas some companies add butane for easier winter starting, as an example. Denver's fuel is modified to help account for the lighter air (i.e., less oxygen per volume entering the engine).

 

Last year I took our 2K Maxima to the dealer for it's 60K
service. I asked about having the plugs changed. The service
advisor of course told me the plugs didn't need changing
until 100K miles. I then told him that the guys on Maxima.org
have been changing theirs well before and noticed fouled
plugs. He then told me that "those guys have not been using
premium fuel. If you use the recommend premium, your
plugs will last to 100K." Reason to use premium?

2003 TwBlue 5AT Sedan, sunroof,
Graphite Leather, splashguards, HKS exhaust,
14 wire Grounding kit, 350Z duct, Stillen CAI
Underbody rear diffusers, Drilled alum pedals

 

Marty,
Thanks for the response. Interesting about Denver, I never knew that. So regarding these regional, seasonal differences, are you saying that they would have no affect on the energy available (sorry if I'm not saying it right) in the fuel? In other words, I knew the Brand Name would have no effect on performance, and I knew what octane did or didn't do, but could seasonal or regional fuel differences effect performance?

Thanks for your comments, very helpful.

2004.5 Coupe/5AT/Ivory/Everything but chin spoiler/Z Tube-Popcharger/Crawford V5 Plenum on the way

 

cato,
There are a half a dozen different types of fouling. Which did they find? Most common I've run across is running too rich, but other fouling can happen. Oil fouling for instance, or lean conditions. Even though the recommended change isn't for 100K, I still plan on inspecting mine every 20k or so.



2004.5 Coupe/5AT/Ivory/Everything but chin spoiler/Z Tube-Popcharger/Crawford V5 Plenum on the way

 

The cost of a set of plugs every 100,000 miles hardly justifies spending $.20 per gallon more for that 100,000 miles. Much simpler choices: take the plugs out at 50,000 miles and clean them; or,since premium usually just has a little more solvent/detergent than regular, put in premium every forth tank; or every forth or fifth tank, add a can of gasoline detergent/injector cleaner.