What octane gas do you run?, Is higher always better ? Or just a waste of $$$ Options

[Jake Raby]

Octane does not equate to a measure of how clean the fuel is.

Nope, BUT having talked to a rep from Chevron when I got a tank of bad 93 octane that melted a 20,000 buck engine on my dyno when it was really 87 octane I'd have to say that the lesser octanes have greater risks of impurities..

He told me that in my area they sell double the amount of 87 octane than that of 93, especially due to the current and recent gas prices. The more often the tanks are filled the greater the opportunity for impurities to be transferred from the tanker trucks into the tanks at the station..

That one instance is the only bad experience I have ever had with 93 octane fuel, I generally use 2500-3000 gallons per year on the dyno alone (as much as 3700 gallons in 2003 when I did a ton of cooling system testing)

Chevron paid for the engine in question because they had filled a 93 octane tank with 87 Octane-

[groot]

What about the newer cars?

My wifes '01 Infiniti says 91 octane. Is it necessary?

Typically, yes, especially on newer cars. Today's calibrations are very complex and if the calibrators used premium, that's what your fuel/ignition maps are based on, not regular.

Ford uses the Jag V8 in the Lincoln LS and the calibration is for premium fuel. But, they were having a problem fouling plugs by the time the vehicles arrived at the dealers. So, they used regular for the 7 gallon plant fill just the keep the plugs from fouling. But then you had customers driving the cars when they arrived at a dealer and they would ping. No wonder Ford's losing money.

[Thorshammer]

Many of you know I work in the motorcycle industry, and fuel is a major problem for several reasons.

At transport: fuel being removed from a sea going tanker, the fuel is not always segregated as previously suggested. but what is normally being shipped by a sea going vessel is the "base stock" of gasoline. This is what is delivered to distribution points and then different companies add their own additive packages. The important lesson here is when the gasoline is removed from the vessel, the removal of weight (fuel) has to be countered or else the ship can become improperly weighted, and that cg needs to be maintained. They do this by pumping sea water into the fuel tanks. Knowing that gasoline is heavier than water, the water stays down and the gasoline goes to the top, allowing for removal. Some one who must be a Mensa member thought this wasn't the very best idea, since that fuel contaminated sea water had to be pumped back out to refill the tank ata later date. In some of the newer tankers this method has been eliminated, by having a ballasting system that counteracts the "pumping off". One major drawback to the first system is the microbiological growth that can form (AND LIVE) in gasoline. It has a much higher chance of surviving in diesel fuel, as Jake and I (and others) know about from our background in aviation. Even though JP4 is good fuel, it can have microbiological growth that can lead to fuel tank sealant degradation, but thats another story, back to the question.

Once the base stock fuel is "refined", meaning the company has blended their additive package into the fuel, then it is normally trucked to a gas station or holding tank for consumers. The other way fuel storage tanks become saturated with water is condensation. This year in New England, we have had tremendous rainfall, and very high humidity. This increases the ground water levels, and provides for more condensation (water) to be distributed to the in ground tank. This can also lead to a ton of problems. Here's what is very interesting about blending, different chemicals that one company claims to "drive your engine clean" can raise the cost of the fuel by 10-20 %. If we know that the base fuel is the same, then we can easily conclude that the different price from regular (87)- super unleaded (93) is the cost of the additive packages. These addditive packages are what raise or lower the octane of the fuel. Some of the additives are detergents, some are octane additives.

The poster that earlier discussed the AKI standard, vs ron or research octane number. PLEASE UNDERSTAND WHAT OCTANE RATING YOUR BEING ASKED TO PUT INTO YOUR CAR. You may be camparing apples to oranges. Also remember that the profit margin on super unleaded will be higher than regular fuel. So it is in the gas companies best interest to market their higher octane fuel to you the consumer. I agree with Jake, listen to the engine, take notes on gas mileage, the engine will tell you.

Another thing in this post that I need to cover is ETHANOL. Most cars (not the 914) have closed loop O2 feedback that will monitor fuel mixture and compensate.
However the 914 is not one of them. Also many early FI systems do not rely on the O2 feedback when at WOT (wide open throttle). What we really need to know about ethanol is that the release of British Thermal Units (BTU's) is less than that of gasoline for the same volume. Meaning: to get the same amount of work from ethanol based fuel you will need more volume of ethanol based fuel to extract the same amount of work or horsepower. My testing on motorcycle engines using a four gas analyzer has shown a .75-1.0 % CO drop when using ethanol based fuel that has an ethanol content of 12%. When this happens, there is actually a RISE in hydrocarbon emissions due to lean misfires. So the EPA mandates this crap, presumably for clean burning, and it actually makes SOME vehicles run worse and produce more hydrocarbons.

On a political note, if ADM (Archer Daniels Midland) got their hands out of the pockets of the Senate and House of Reps, we would'nt have to deal with this shit.
Anyone thinking E85 (85% ethanol) is a good thing, needs to get a clue. Imagine how much more E85 you will need to burn to get the same power out of your car when using E85. This is not a smart plan. Forget about gas mileage or cost per mile of E85. The byproduct of straight ethanol can be very corrosive, you can plan on less engine life, and far more frequent maintenance visits for your car if you run E85. What a farce!

But anyway, what gas should you use in your car. The minimum octane so it doesn't ping, and does'nt run lean. I have always run my stock 914's on 87 octane fuel. Also remember that with carbon build up, your compression ratio could go up a little, and this may force you to run a higher octane. Again, only use the octane needed so it does not detonate. Anything else is an absolute waste of time......and money.


Erik Madsen

[rjames]

He told me that in my area they sell double the amount of 87 octane than that of 93, especially due to the current and recent gas prices. The more often the tanks are filled the greater the opportunity for impurities to be transferred from the tanker trucks into the tanks at the station..

Couldn't the opposite be just as true? (Assuming that they don't clean out the holding tanks at the station.)

If a holding tank for 91 octane does get filled with gas that has impurities, then that gas sits in there longer (as people don't buy it as much). Therefore it's possible that it could actually increase the chances that your buying a tank full of gas with impurities as apposed to the low octaing holding tank that is being refilled more often. I guess you'd have to factor in how often you by gas vs how often a holding tank is being refilled.

[Jake Raby]

Eric, That was an excellent post!

[Michael N]

Thanks for all the input.

I have been running 91 octane in my car and it seems to be running well. I am going to drive the hell out of my car this weekend and wanted just a little more. The local 76 station sells 100 octane at the pump so I was thinking of running it hoping for just a bit more power. At @ $4.50 a gallon I was trying to decide if the extra octane may be worth some extra power. From what I can take from the answers I feel that I may just stay with the 91 octane.

I am running a 2.4 litre 6 from a 1973 911S with MFI and the compression is 8.5:1 . It runs like a raped ape with the 91 octane but I just wanted a little more kick for the weekend. For a extra $2.00 per gallon, I thought it might be worth a try.

[Jake Raby]

If its been running fine on 91, leave it as is. Higher octane fuel, as stated above requires more CR to burn or advanced timing. If you have carbs don't be suprised if you need larger jets because the fuel viscosity is actually higher.. MFI can act similarly due to its characteristics.

So many times I see guys go to the track, dump in higher octane and then the car GOES SLOWER!!!!!!

If you don't want to retune a street engine won't make any more power on higher octane fuel if it lives well on pump gas normally.... BUT the engine will run a tad cooler..

If it runs fine keep your normal fuel in the tank...

[Michael N]

Thanks (IMG:style_emoticons/default/biggrin.gif)

Now off to do some (IMG:style_emoticons/default/driving.gif) (IMG:style_emoticons/default/driving.gif) (IMG:style_emoticons/default/driving.gif)

[Crazyhippy]

If you put higher octane in.. turn up the boost too (IMG:style_emoticons/default/biggrin.gif)

I can safely run 18PSI on pump 91, but 22PSI on 108 VP. The 108 gets a bit more timing too

BJH

[Leo Imperial]

Erik,
What you posted is interesting. I do not wish to dispute any information other than that which is related to tankers. That is false information. CG is not maintained by displacing the cargo with sea water. The only displacement taking place is inert gas. I don't work in the motorcycle industry, so I will not comment on that. I will stick to the Maritime Industry which is my profession. I am curious to know what the classification of "base stock" is and what percentage of this stuff is transported in this form on clean product tankers? You seem to think that what I said was false, as it pertains to segregation. It is not. I wont even start to explain why even referring to CG as you did shows that you don't know.

[gfulcher]

Finding a sunoco with 94 octane ULTRA is like finding extra power with my Dellorto carbed, slightly modified 2.0 4-banger. Actually akin to pulling the bunched up floor mat out from behind the gas pedal in a typical car.... whatever those are..

-greg-

[shelby/914]

No test results, or reems of data, just that my life long Porsche mechanic & origional 6 racer said that 91 was not necessary. He said that I could use regular, which at altitude is only 85 octane. No problems yet although I do sometimes put in some 87. (IMG:style_emoticons/default/confused24.gif)

[mikerose]

As high as available otherwise it runs like dodo.

(IMG:style_emoticons/default/agree.gif)

When I use 87 my 914 will miss everytime . But when I use 92 or better there is never a miss (IMG:style_emoticons/default/biggrin.gif) This for me was a hard lesson to learn.

[effutuo101]

How often do the tanks get tested? once a year? I use 91 octane, but have noticed a variance in performance and milage from one tank to the next. Does anybody make a small test kit? I would love to be able to walk into the attendant and say, Why am I paying for 91 when the test here shows 87?

[Air_Cooled_Nut]

My $0.02...
Gas is LIGHTER than water. Erik, I know you know that by your description, just that you wrote "heavier" by mistake.

I don't know about gas tankers, but on my ship, a Spruance-class Destroyer, our engines were gas turbine units (4 @ ~20,000hp each (IMG:style_emoticons/default/piratenanner.gif) ) and they used JP5 (jet fuel, which cars don't use). To balance the ship when fuel was transfered 'tween tanks sea water was used to "fill the gap". Since Combat Systems berthing -- where my rack (bed) was -- was directly on top of the fuel tanks we got to hear the loud transfers every time it happened. Point is, some ships use this method and some don't. For transporting gas I would think they would use methods to reduce polluting the product and filter/clean it as well before land transporting.

I run low grade in my 914 since she's stock. My other air-cooled (bigger engine) gets high octane due to higher compression and is jetted accordingly. Because I don't drive her as often the extra cleaning package that comes with the higher octanes give me the warm-n-fuzzies as well. My Jetta -- a daily driver and weekend SCCA'er -- gets high octane as well due to higher compression and as recommended by the after-market chip manufacturer (Techtonics Tuning here in Orey-gun).

I don't see the higher octane fuels as a complete waste of money since they contain their cleaning pacakages. And what swood wrote is the chief reason for high octane.

[swood]

finally....some much needed validation in my life. (IMG:style_emoticons/default/smile.gif)

[RickS]

The owners manual recommends 92. I figured the engineers did it for a reason, other than owning gas stock.

[TravisNeff]

In my stock injected 2.0 I ran regular (87 in AZ), sometimes midgrade (89 in AZ). For my stock injected 1.7 I ran super (91 here in az). So the extra MPG on the 1.7 was negated by the use of regular on my 2.0 - tank for tank.

[fitsbain]

Lower octain gas burns hotter and makes more power when compaired to the same motor running high octain gas. It also detonates easier.
But higher octain gas can be squeezed more, thus making more power as the lower octain would detonate too soon.

[D1A3]

I run 87 on my stock 2.0 engine as recoemnded by Porsche on the sticker under the hood of my '76. I have never really seen much if any diference between the 87 and 93 octane fules. te only time I use 93 now is if I am also putting in a bottle of injector cleaner. Not sure why, but I feel like it is better to do it that way, although I have no evidence.

I was thinking about the octane ratings between the US and Europe a few weeks ago and when I was on my way to Stuttgart I popped off this picture of a pump there that clearly shows 91 ROZ is the equivalent of regular here in the states.



--Jason