Use the lowest octane that works without pre-ignition.
Use the cheapest brand of that octane you can find.
Spending more will guarantee nothing.

Quality gasoline? All are made from the same crude and to the same standards. The only big difference is the color of the delivery truck.



Post Edited (Jan 27, 11:15am)

 

The octane rating for a fuel is related to the burn rate and the tendancy to predetonate or 'ping.' Typically, an engine is designed to have a particular compression ratio, and this ratio determines what octane fuel is required for the engine. Running too low an octane rating will cause the engine to detonate, resulting in damage. Running the correct octane will correct the problem. Running too high of an octane is basically a waste as the increase in octane does nothing to improve the efficiency or power of the vehicle, and may even reduce the power output.

In some cases, buildup on the internal surfaces of an engine over time will effectively increase the compression ratio. One solution to this is to use a higher octane fuel than the engine was designed to use. However, a lot of the time if an engine is detonating, it is due to some irregular surface in the cylinder (burr), and so increasing the octane of the fuel again has no effect, and is basically a waste.

There is no harm in running a higher octane fuel than is required, however you are not really buying 'better' fuel. Many people feel that there car runs better on premium, although I tend to think most people are fooling themselves. There are many vehicles that require premium, but typically NA z's are not one of them.

Turbo cars are a different story. I don't know enough about the turbo models to tell you if they 'really' need higher octane, but I would imagine that any time you increase the boost beyond the factory setting, you are basically increasing the compression ratio, and so higher octane fuel may be required. Turbo also increases the temperature of the intake air, which also increases the tendancy to detonate. When dealling with turbo, it is probably better to err on the side of caution and use a premium fuel.

 

your car will run fine on cheap gas. thats what the previouse owner of my car put in. I use medium, because my parents think I should in my car, and they pay for my gas..hehe

 

Just a note you can get good gas anywhere and you can get bad gas anywhere......but I'd be wary of anywhere where it is alot cheaper than other places.

 

Always buy from the busy stations. Less chance to get watered down (condensation) fuel.

 

If there is a row of gas stations, I tend to go with Chevron, but that's just a personal preference.

In my area, all the gasoline to supply the region comes thru one pipeline, whereupon it is distributed to the tanks of the various oil companies, so I know that the basic stock of gasoline is the same. What I don't know, and what very few other people know, is what happens to the basic gasoline after it is routed to different tanks.

I will state that, while diagnosing Z cars with various ailments, I have pulled fuel samples out of the tanks and have gone to the gas stations to purchase gas for those dweebs that bring the car to me completely empty and want it road tested, and have seen gas that is sparkling clear all the way to stuff that is hard to distinguish from milky pond water. I believe, as a general rule, that name brand fuels tend to be filtered better, and
receive the additives and octane modifiers supplied on a proprietary basis by the parent petroleum company. This is what the oil companies want us to believe. However, this does not prevent an individual station owner from cheating with octane (selling low octane as high octane) or adulterating the fuel that he/she sells. (Station owners have been caught disposing of waste oil by mixing it into their underground gasoline tanks)

My personal Z has high compression, and is very sensitive to octane. With high quality 93 octane gas, it runs OK with an occassional ping here and there. This makes the car a good BS detector. I have purchased both name brand and off brand fuels for this car, and more times than not, my car runs OK on name brand fuel most of the time and rarely runs OK on off brand gas, but I cannot state with unerring authority that name brand gas is consistently superior, so I tend to gravitate to Chevron with the Z, but not exclusively.

So my recommendations are: purchase the lowest octane your car will run on acceptably without pinging at High Volume gas stations. Avoid "gasohol" if you drive a fuel injected car. If you find decent gas in your local area, return regularly to that station. Avoid fuel from places that aren't in the primary business of selling gas.

 

Also go for the newer stations with fresh concrete work. This means that the tanks have recently been replaced and won't have as much crud in the bottom.

Completely off topic and unrelated, but yet related question. I have always run premium gas in my 2-stroke dirt bike and have always had a very wet, oily exhaust when I trail ride. I was thinking the other day that this might be due to the cooler burn of the higher octane gas resulting in more raw oil emissions. I have tried different plug heat ranges with no change to the exhaust grime. Buddies that run the same oil brand have much less oil buildup in the silencer than mine, but their bikes run no better, nor foul any fewer plugs than I do. The carb is tuned such that I rarely foul a plug and get a perfect tan spark plug color. I think I will try regular or mid grade next time and see if it helps.

 

I was just going to mention that. Try to get gas from the new stations, or the ones that have had their tanks replaced recently.

 

here we go on the octane thing again

 

what exactly is an "off brand" or a "name brand"??------i cant imagine any one at the refinery or a truck driver doing anything different to the additives/octane rating.....if that happened it would be a BIG deal...now what an individual does at his store could be anyones guess...even that is unlikely.if you constantly have problems with a certain place it may be getting water into the tanks or ??? i would avoid that one particular place.at the refinererys you will see various different fuel trucks being filled up..one right behind the other.i cant imagine them doing anything different to one truck and not the other.

 

You do not see trucks being filled at "refineries". You see trucks being filled at "distribution terminals". Each petrol company has its own distribution point within that terminal generally. The great big storage tanks say "SHELL", "CHEVRON", "EXXON" , "BP", "AMOCO", "CITGO" and so on ("Name Brands"). the "Shell" tank truck goes to the big "SHELL" tank and fills up at their spigot. The tanker trucks that say "Billy Bobs Oil Transport" go over to the big storage tank that says "GOLLY GEE OIL COMPANY" and fill up at their spigot and deliver gas to "Getty Marts", "Billie Sue's Deli and Fill'er Up", "Dave's Independent Service Station" , and "7 Eleven".

Now, class, what is "name brand" gas?

 

I am with the Z doctor. AND if any of you care to look most gas stations, at least in my area (I think it may be required), tell you the amount of certain "detergents" in each octane. I believe chevron puts the same detergent in all of octains but I don't remember. One method to increase octane is to add methanol which will reduce your power output so watch that one. I havn't ever noticed a difference in my Z (stock and un-tuned).

 

this might clear things up

Two benefits to higher octane gas:
1) You can run a higher compression without pinging - higher compression netting you more power.
2) You can advance your timing further without pinging - advanced timing netting you more power.
In short, running higher octane gas in and of itself doesn't net you anything (negligible at best), but it may allow you to tune your car to the point that you do see gains from the higher octane gas. Older Z's (correct me if I'm wrong) don't have knock sensors and don't adjust your timing on the fly to the quality of gas you and therefore wouldn't be as affected by the quality of gas, provided they were tuned to not knock with lower octane gas. Some newer cars that require premium will actually retard their timing if they sense knock in the engine, thereby reducing power. Newer cars that aren't designed to run premium will not usually advance their timing beyond what works for lower octane fuels and therefore don't really gain anything by filling them with premium.

 

With all honesty, I tend to go with Shell because I am an avid F1 fan.
The big brand names tend to have better facilities and processes that refine the gasoline. Their higher price also justifies the additives and cleaners that are in their gasolines. Also, the big brands also have more resources for R&D of new "better" mixtures of fuel. Finally, those brand name stations generally tend to be cleaner and new looking. Therefore, I tend to trust names like Shell to fuel my car.
There is a lot of sulphur contaminants in crude oil. I heard from a chemistry professor that the unknown sulphur gas smell from cars come from poorly refined gasoline.

I rarely go to a generic gas station to fill up my entire tank. In my short 5 year history of driving, I have noticed no difference in performance between any brand name gasoline.

 

High octane is definately required with turbos. With 87 octane, my zxt will ping above 4000rpm. The gas I buy is whatever is cheapest, usually at the Loveland 7-11. The gas you buy is all the same. Additives are mixed in at the distribution points.

 

Shell and Texaco are the same. Exxon and Mobil are the same. That's the only places I get gas. Used to try the cheap places. Had loads of watery-gas problems with racetrac. Wal-mart gas seems to be fine. Not every place gets their gas from "mr. trucker." Wal-Mart's petrol comes from Arkansas. Different companies get from different places. Amoco (does BP own them now?)'s doesn't run as good as my four picks, it is crap (or so it seems). I'm using the SU carbs, and i'll backfire if i run anything less than 91 at one of those four places. I can run 93 outta a racetrac and STILL backfire. I'm not worried about pinging, the backfiring's what warns me. And obviously there IS a difference because the ONLY places i haven't backfired the gas are those four: Shell/Texaco, Exxon/Mobil. I'd like THAT to be explained by the "everybody's gas is the same" type people. ESPECIALLY living/working in a populous area where ALL the gas stations i've used are new.

mnelson_260z

 

As to the newer in ground tanks always being better, that is not true. I used to be a minit market manager and our tanks had a warning system for when there was over 3% water in the tanks, when its over that limit, we had to get the water pumped out. Under that and everything was fine. the gas that we got was inexpensive but still rated as the name brand(amoco in this case). We managers were taken on a tour of the refineries in Reading, PA and were shown how this is done for additives and stuff. First, you place your order for 10k gallons of gas. A tanker then goes to the refinery and gets a basic load of gas, without additives. Then the tanker goes to a separate station, which shoots that particular brand's additives into the tanker's tanks. Then you have your particular brand of gas. The only brand that I know of that still does NOT do this is Sunoco brand gas which put the additives directly into the refined gas immediately after basic gas manufacture. My brother in law has worked for them for 35 years, and took me on a plant tour in Philadelphia Pa, so I saw that for myself, as well.

 

Until you make mods that require you to raise your fuel level most Z will run on plain jane. Just wait until you build something that needs some C12 at $4.50 / gal and you can't even pull up to the pump! You carry it home 6 gals at a time in your own fuel can. NOTE: while doing this it is not wise to light a Cigaratte when using your normal Z to bring you Baby Z a drink... LOL

Sorry it is long but this comes from the Federal Trade Commission

The Low-Down on High Octane Gasoline

Are you tempted to buy a high octane gasoline for your car because you want to improve its performance? If so, take note: the recommended gasoline for most cars is regular octane. In fact, in most cases, using a higher octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner. Your best bet: listen to your owner's manual.

The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel. This happens to a small percentage of cars.

Unless your engine is knocking, buying higher octane gasoline is a waste of money, too. Premium gas costs 15 to 20 cents per gallon more than regular. That can add up to $100 or more a year in extra costs. Studies indicate that altogether, drivers may be spending hundreds of millions of dollars each year for higher octane gas than they need.


What are octane ratings?

Octane ratings measure a gasoline's ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders. Most gas stations offer three octane grades: regular (usually 87 octane), mid-grade (usually 89 octane) and premium (usually 92 or 93). The ratings must be posted on bright yellow stickers on each gasoline pump.


What's the right octane level for your car?

Check your owner's manual to determine the right octane level for your car. Regular octane is recommended for most cars. However, some cars with high compression engines, like sports cars and certain luxury cars, need mid-grade or premium gasoline to prevent knock.

How can you tell if you're using the right octane level? Listen to your car's engine. If it doesn't knock when you use the recommended octane, you're using the right grade of gasoline.


Will higher octane gasoline clean your engine better?

As a rule, high octane gasoline does not outperform regular octane in preventing engine deposits from forming, in removing them, or in cleaning your car's engine. In fact, the U.S. Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.


Should you ever switch to a higher octane gasoline?

A few car engines may knock or ping - even if you use the recommended octane. If this happens, try switching to the next highest octane grade. In many cases, switching to the mid-grade or premium-grade gasoline will eliminate the knock. If the knocking or pinging continues after one or two fill-ups, you may need a tune-up or some other repair. After that work is done, go back to the lowest octane grade at which your engine runs without knocking.


Is knocking harmful?

Occasional light knocking or pinging won't harm your engine, and doesn't indicate a need for higher octane. But don't ignore severe knocking. A heavy or persistent knock can lead to engine damage.


Is all "premium" or "regular" gasoline the same?

The octane rating of gasoline marked "premium" or "regular" is not consistent across the country. One state may require a minimum octane rating of 92 for all premium gasoline, while another may allow 90 octane to be called premium. To make sure you know what you're buying, check the octane rating on the yellow sticker on the gas pump instead of relying on the name "premium" or "regular."

 

Thanks for the info.....CYIND

 

FWIW.

81 ZXT. Daily driver. Engine is bone stock with 154,000 miles, running stock boost.

I use 87 octane (regular). Runs fine all the way to about 5000 RPM at which time it starts to knock like a diesel. Since I don't normally spool up the that RPM, I seldom ever have a problem. Even at full boost, going uphill on a hot day, car runs fine with no knocking.

Sam