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

[Michael N]

I was wondering what most drivers are using in their 914's. 87, 92, 100?

I have heard that in fuel injected cars running with a higher octane gas than they were designed to run at can be a waste of money since they are set up to run on a specific octane and any more is lost. I have a Passat and the manufacture states 92 octane. My truck uses 87 and the dealer said I can do damage by running 92 ( although I have no idea why).

Please set me straight on my ignorance. (IMG:style_emoticons/default/sad.gif)

[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