Villian

I believe the 955 Cayenne S calls for any unleaded fuel with a min. octane rating of 91..is this correct? I assume this rating is for sea level?

Has anyone used anything else? What is everyone in the high altitude group running? I've always run premium or the highest that I can get where I'm at..87-91, but I'm wondering with the knock control feature if I could use something lower and get away with it? 85-87. Reason being that where I'm at the price difference between low/mid grade (Usually the same here..only 2 choices..mid/low and premium) and premium is like 25%. That translates to some real money over the course of a year. If the difference between grades was a measly 10 cents then I wouldn't be posing this question..but therein lies the problem..

5thlilpiggy

Im pretty sure that using lower-than-recommended octane results in worse MPGs.

It isnt a 25% loss, but the cost does even out a bit due to this.

dryadsdad

Lower octane means less power down to the standard first tier regular. Below then and you are endangering your engine. I use 91 unless I can find 93.

Shawn Stanford

I always use 93.

HOiYA

I wish we got 93 in CA, instead of just 91.

Borntovin

Always use 93 here in Texas.

hahnmgh63

92 here in Washington, and yes at Sea level. They sell "Up to 10% Ethanol" here but occasionally I get 100% gasoline www.pure-gas.org when I can. It costs more but it actually does make a noticeable increase in mileage and driveability.

PCA1983

Octane does not affect fuel economy. It does adversely affect power, especial at low altitudes and at high operating temperatures (and at high boost for turbos). Here in Central FL near sea level, I use strictly 93 octane which is under $2.60/gallon now at the low price stations. Sam's/BJ's/Costco only offer 87 and 93 but their 93 is at such a small premium that is crazy not to buy it. With the Sam's Club MasterCard, you get 5% cash rebate on gasoline purchases (and at Wal-Mart too), so there is nothing to resist there.

CDMC

I would be more concerned about the additive package than the octane, as a poor package can result in carbon build up over time where a top tier gas would not. As far as the octane, you may see a very minor difference in power, but it will not hurt the engine. Some informative reading:

http://www.nytimes.com/2008/08/03/au...TANE.html?_r=0

http://www.caranddriver.com/features/regular-or-premium

For those who don't want to read the links, from the NY Times article:

Porsche, for example, acknowledges that any of its modern production cars can be run on regular fuel without the risk of damage.

A spokesman for Porsche North America, Tony Fouladpour, added a caveat. “If you want the car to perform at its maximum capability, the best choice would not be 87,” he said. “But we do not forbid it.”

Specifying premium fuel lets a car manufacturer squeeze out more horsepower. BMW, for example, recommends that all the cars it sells in the United States use premium fuel, but they will run on regular.

“There generally isn’t any harm done to the engine by using lower-octane fuel,” said a BMW spokesman, Thomas Plucinsky. “Because our engines do have very good forms of knock sensing and are able to deal with lower-octane fuels, you will not have any drivability issues. You will, however, lose some of the performance.”

mcbit

As usual Porsche has something to say about this in the manual:



I would consider the 6.6% - 9.8% loss of power experience by the two european cars in the 'car and driver' test to be significant.

Personally I use 98 RON exclusively unless I'm low on fuel and it isn't available. There is a noticeable difference in power and despite comments to the contrary a measurable difference in fuel consumption when using 95 RON.

hahnmgh63

Octane will affect your gas mileage and power if the engines tuning (Boost, compression, timing curve) were designed for the higher octane. In that instance the ECU will detect impending knock from the Knock sensors and retard the timing (which will decrease power/mileage) in order to keep the engine from getting damaged. Now if you tried to pump 80~85 octane from Mexico the octane may be too low for the engines ECU Maps to pull timing but our regular would probably be ok but then yes, you will be sacrificing some power and mileage.
P.S. There you go as mcbit posted. Porsche engineers know what they designed into the ECU maps. Now they probably designed in some margin for error but your on your own if you want to push it. And yes, in a normally aspirated engine the Octane requirements decrease with altitude (density altitude). Maybe someone here knows the magic answer but years ago Porsche claimed that there Turbo engines made factory power up to 5000', anyone know? If so they would need the proper octane up to that altitude to develop maximum power.

CDMC

Keep in mind that was on the 6 cylinder M3, which has extremely high output for its size (about 110 hp/liter) and a turbo engine in the Saab. For the V6 and S, which are not nearly as highly tuned, the power loss would would likely be in the less than 2% range. On the turbo, I could well see it losing 10%, especially on a hot day.

TomF

If you are in Seattle, my buddy just bought one of the only stations that sells pure gas. It's on 35th and about 85th...

I have yet to use the pure gas in my CTT. I am anxious to try it!

Aloha,
TomF

wrinkledpants

If you run less than 91, the ECU will pull timing if it needs to. Because the entire ignition process is predicated on the air/fuel mixture igniting at precisely the right time with a burn speed and energy that's established before hand, you'll run less efficiently with anything less than 91 octane. It's one thing to say "you can burn something" it's something entirely different to say "you'll optimize something." The engineers would have had to create fuel tables for each of the various octanes for you to be able to use 89 or 87 octane with no ill effects. Instead, they built in knock detection to prevent you from burning the motor down. This is also why a single tuner might offer two different tunes - one for 91 and one for 93. You'd think that just buying the 91 octane file and putting in 93 octane fuel would net the same results, but that's now how it works. Gotta remember that WOT is open loop, meaning that it's basically a crap load of "if this, then that" statements. "If this MAF reading, and this temperature, then this much fuel for ideal AFR." There isn't a feedback mechanism for adjusting the AFR in open loop as the oxygen sensors are ignored. It's not reading something and making adjustments the same way it does in closed loop when you're cruising on the highway. If the car runs out of timing retard, then it'll override your right foot and close the throttle plate as a way to reduce power. You do that enough, and it'll throw a code as it figures there must be something wrong if you're maxing out the timing retard.

If all you do is gentle driving and never go WOT, you'll be totally fine with 89 octane, sans a slight reduction in mpg. You'll see a small difference here because the ECU is under the impression you've put in fuel that is at least 91 octane, and will burn in a certain way. When you put in something else, it ends up burning differently, and has to adjust to account for this. This is why you typically see a slight degrade in fuel consumption when running less than 91 - maybe 1 mpg or so. This isn't a flexible fuel vehicle that can *efficiently* run a variety of octanes and fuel sources.

People get the idea that 91 octane is the maximum you need to attain perfect performance at sea level, and once you leave sea level, that requirement changes in octane as you increase in altitude. This is true if you're thinking about detonation, but you also have to remember that "resistance to detonate" also means it has a slightly different burn characteristic in the combustion cycle, and that doesn't change with elevation. Porsche isn't spec'ing premium fuel because they get some kind of kickback in fuel sales. It's a minimum requirement because the entire fueling system is predicated on the burn characteristics of 91 octane. It's a bonus if you get 93 octane, and while the ECU can capitalize on it a bit, it's not the same as if you were to actually get a tune where the open loop maps are adjusted for 93. Look at how much detail Porsche goes into in the manual for tire pressures and how it relates to loads and temperature Detonation is only part of the reason, the other reason is how 91 burns compared to 87, or 85 if you're in the mountains.

Will you hurt the motor? No. The ECU has the ability to save itself from the driver. Will you notice a difference? Yes. A reduction in mpg on normal driving, and power reduction at WOT. My math if you drive 15K miles a year at 15 mpg supports a monthly cost savings that's the equivalent of 1.5 subway sandwiches a month. Hardly seems worth it.

mcbit

Keep in mind that I was merely commenting on the test results as presented.

...however the e46 M3 gets it high power from running a high rev limit whilst the torque output of the 3.6 Cayenne is a little higher than that of the M3, it is a highly tuned engine. The main difference between the M3 and the Ram, Mustang and Accord is the compression ratio which is 11.5:1 in the M3 and less than 10 in all of the others. The Cayenne V6 and V8 also run CRs of +11.5:1 which demand the use of premium fuels for efficient operation and are likely to suffer far more in terms of power loss than the lower CR examples quoted in the test.