91 vs 93 octane
The manual asks for 93 octane, but in my area I can't seem to find higher than 91. Will the ECU automatically compensate for this, and what is the implication? I've seen in some other posts that the ECU is programmed for a specific octane...
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RE: 91 vs 93 octane
What year car are we talking about?
Lee |
RE: 91 vs 93 octane
It's a 2001...
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RE: 91 vs 93 octane
I would ask the dealer, but all modern cars now can take a little lower octane. The newer cars like yours have anti knock sensors and they will adjust timing along withother alogorithems so the car does nor knock or ping.
Ask or call a dealer but for me i would use 91 if it does not ping or knock you are good to go. If you prefer you can go to a autostore and buy octane enhancers. I have never used them by my drag freinds say they work well on cars with high compression. Alot of people use high test fuels in cars that cannot use it. High compression engine use it for antiknock protection and better performance. new vehilces that the maunfacturer suggests 87 octane will actually give less gas milage and no better perforamnce if 93 is used. This is different from olden days caused by modern electronics. Lee |
RE: 91 vs 93 octane
Cool, thanks Lee!
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RE: 91 vs 93 octane
91 is fine in your car. We can't get anything above 92 in Kansas either. The ecu will adapt, especially with the anti-knock.
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RE: 91 vs 93 octane
I'll bet the original poster is located at a high altitude. I could be wrong, but I thought the Octane rating was affected by the altitude, such that 91 rated gasoline out here in Colorado (5000 feet and higher) was actually physically and chemically identical to 93 rated gasoline at sea level.. It would make sense that it's 92 in Kansas - half way
between the two extremes. So the original poster is running the recommended gas for his vehicle, it's just rated different at altitude.. - RA |
RE: 91 vs 93 octane
RA,
You are right in the impact of altitude on engines and detonation. Airplanes use 100 oct fuel because they need the extra protection against premature detonation that can cause engine damage over time and a landing where you had not planned. Airplanes have to "lean" out the mixture as they go higher to maintain the proper stoichiometric mixture to obtain maxium engine output. For the atlitudes cars go incluidng Leadville at 9200 feet the cars electronics can handle this.On old cars or carburated Harley Davidsons the driver can tell the difference. Cars today take this into account with the design electronics in the car.Thus is especially truefor fuel injected cars. Lee |
RE: 91 vs 93 octane
Actually I'm in San Jose, CA. Pretty close to sea level. I guess CA mandates the lower octane premium gasfor better emissions. But I'm not sure...
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RE: 91 vs 93 octane
ORIGINAL: ladams1 For the atlitudes cars go incluidng Leadville at 9200 feet the cars electronics can handle this. to the ski places in CO, is just over 11k), and sometimes close to 12k (Loveland Pass, if you don't want to go through the tunnel) On old cars or carburated Harley Davidsons the driver can tell the difference. you still gotta downshift and keep the revs up a bit higher. And we pass a *lot* of cars chugging along at 40 mph or so... High altitude is where a turbo makes a *huge* difference - my wife's previous car was a turbo Saab, and that sucker would pull hard all the way up to the top of the pass. Ramming all that air into the pistons helps a lot when the air itself is thinner... Can't afford a turbo Porsche ;( I'm in the process of buying a normally aspirated 911 c4.. it'll be interesting to see how well it handle's the altitude. I suspect it'll be like my wifes BMW - fine as long as you keep the revs up a bit. - RA |
RE: 91 vs 93 octane
ORIGINAL: 911fiend Actually I'm in San Jose, CA. Pretty close to sea level. I guess CA mandates the lower octane premium gas for better emissions. But I'm not sure... certainly can't get anything higher than 91 statewide, and as far as a I know, the dealer's don't do anything different with the cars around here than anyplace else.. and there's all kinds of Porsche's running around places like Vail and Aspen, so they must be able to deal with it ;) - RA |
RE: 91 vs 93 octane
ORIGINAL: rarctor ORIGINAL: ladams1 For the atlitudes cars go incluidng Leadville at 9200 feet the cars electronics can handle this. to the ski places in CO, is just over 11k), and sometimes close to 12k (Loveland Pass, if you don't want to go through the tunnel) On old cars or carburated Harley Davidsons the driver can tell the difference. you still gotta downshift and keep the revs up a bit higher. And we pass a *lot* of cars chugging along at 40 mph or so... High altitude is where a turbo makes a *huge* difference - my wife's previous car was a turbo Saab, and that sucker would pull hard all the way up to the top of the pass. Ramming all that air into the pistons helps a lot when the air itself is thinner... Can't afford a turbo Porsche ;( I'm in the process of buying a normally aspirated 911 c4.. it'll be interesting to see how well it handle's the altitude. I suspect it'll be like my wifes BMW - fine as long as you keep the revs up a bit. - RA Agreed, cars losepower at altitude, less oxygen. The modern cars adjust the fuel flow, timing etc so the car does not runrichor foul. I am sorry I did not make my point clear. My CARB Harley at 7700 ft was much harder to start, ran rough and was a very rich mixture. My freind on the fuel injected harley had no problem and it was 3 years older. I bought a fuel injected model within a month. Good luck on your future Porsche purchase.I suspect you are right on how it will act. Is your Saab turbo or supercharged? I was trying to work out in my mind if a turbo or supercharged would be better at high altitudes. Thanks, Lee Lee. |
RE: 91 vs 93 octane
ORIGINAL: ladams1 Agreed, cars lose power at altitude, less oxygen. The modern cars adjust the fuel flow, timing etc so the car does not run rich or foul. I am sorry I did not make my point clear. My CARB Harley at 7700 ft was much harder to start, ran rough and was a very rich mixture. My freind on the fuel injected harley had no problem and it was 3 years older. I bought a fuel injected model within a month. Good luck on your future Porsche purchase. I suspect you are right on how it will act. Is your Saab turbo or supercharged? I was trying to work out in my mind if a turbo or supercharged would be better at high altitudes. - RA |
RE: 91 vs 93 octane
Ra,
Congrats on your new Porsche. They are womderful cars. Enjoy, Lee |
RE: 91 vs 93 octane
FYI, I remembered reading this discussion a while back when I came across this in my owners manual (pg 177):
"Your engine is designed to provide optimum performance and fuel economy using unleaded premium fuel with an octane rating of 98 RON (93 CLC o AKI). Porsche therefore recommends the use of these fuels in your vehicle. Porsche also recognizes that these fuels may not always be available. Be assured that your vehicle will operate properly on unleaded premium fuels with octane numbers of at least 95 RON (90 CLC or AKI). since the engine's "Electronic OktaneTM knock control" will adapt the ignition timing, if necessary." So there you have it. 91's OK although 93 is preferred. |
RE: 91 vs 93 octane
" So there you have it. 91's OK although 93 is preferred."
Don't totally agree. If switched to 91 octane and the car doesn't ping at first, then it never needed the 93 in the first place. Octane requirement is a function of maximum cylinder pressure. Max. cylinder pressure is established by many things, including compression ratio, ignition timing, intake valve closing point, engine load, RPM, throttle opening, fuel burn rate (including octane and combustion chamber design), driving style, and others. If the computer has to retard timing to accomodate lower octane fuel, then you are losing power and the octane is substandard. But if the timing is not retarded from knock sensor feedback, then any increase in octane is useless. Many think that cars are faster with higher octane. The truth is that octane is like money...... any more than you need is a waste. OK so that's a bad example but you get the point. |
RE: 91 vs 93 octane
Hey, I'm just telling you what's in the FM (that's "fine manual," as in RTFM), you can argue with Porsche if you want but the manual says what is says.. "optimum performance and fuel economy" "with an octane rating of 98 RON (93 CLC o AKI)."
The ECU can most likely detect and adjust for lower octane fuel well before you'd actually notice a ping. So you could go ahead and put lower octane fuel in there, and never here a thing - but your car might not performing to it's best. Of course, some of us have no choice, because 91 is all that's available.. and apparently, you can put 90 or 91 in the tank without harming anything (although you may not run as well) - which is what this thread was all about anyway. - Nick |
RE: 91 vs 93 octane
Again I'm sorry. I've seen the results of ESC (electronic spark control) based spark retard. Admittedly it was on a number of non-Porsche engines. The systems all worked basically the same. The knock sensor (essentially a frequency-tuned piezo electric microphone) is excited by engine knock sound waves travelling through the engine block. The computer has an algorithm to react after a preset amount of knock signals arrive at the sensor. This is presumably done to eliminate false triggers that would inevitably occur. The computer pulls out spark and remembers the occurance. If the situation happens again, it pulls out more spark and remembers. The net result is that the driver feels, after switching to sub-octane fuel, there is noticable ping immediately on high load. This is only for a second or so. Next time the engine is loaded even more severely, it may happen again. Usually, there are three or four instances of ping before the timing is retarded enough to eliminate knock. This can be verified by connecting an OBD scanner and reading the spark retard numbers.
Undoubtedly, Porsche has taken a substantially conservative approach to the recommendation they publish. In some cases, the extra 2 points is necessary. In some cases, it's not. In my opinion, the combustion chamber is too efficient, the compression ratio too low, and the operating RPM range too high to warrant octane above 91 being necessary in most conditions. There are situations that would warrant higher octane. One example would be a driver that uses too much throttle at too low an RPM in too high a gear. Another possible explanation for the recommendation is that Porsche would have us believe that their cars defy the natural laws of physics and engineering, subscribing to an elite set of scientific principles exclusively. Sadly, they are simply machines and must dwell in the same kingdom as other more lowly but equally obedient machines. BTW I must humbly apologize for hijacking this thread from the harmfulness of 91 octane to "Will the ECU automatically compensate for this, and what is the implication?" I mistakenly thought I read this in the original post. |
RE: 91 vs 93 octane
ORIGINAL: wdonovan Again I'm sorry. I've seen the results of ESC (electronic spark control) based spark retard. Admittedly it was on a number of non-Porsche engines. The systems all worked basically the same. The knock sensor (essentially a frequency-tuned piezo electric microphone) is excited by engine knock sound waves travelling through the engine block. The computer has an algorithm to react after a preset amount of knock signals arrive at the sensor. This is presumably done to eliminate false triggers that would inevitably occur. The computer pulls out spark and remembers the occurance. If the situation happens again, it pulls out more spark and remembers. The net result is that the driver feels, after switching to sub-octane fuel, there is noticable ping immediately on high load. This is only for a second or so. Next time the engine is loaded even more severely, it may happen again. Usually, there are three or four instances of ping before the timing is retarded enough to eliminate knock. This can be verified by connecting an OBD scanner and reading the spark retard numbers. Undoubtedly, Porsche has taken a substantially conservative approach to the recommendation they publish. In some cases, the extra 2 points is necessary. In some cases, it's not. In my opinion, the combustion chamber is too efficient, the compression ratio too low, and the operating RPM range too high to warrant octane above 91 being necessary in most conditions. There are situations that would warrant higher octane. One example would be a driver that uses too much throttle at too low an RPM in too high a gear. Another possible explanation for the recommendation is that Porsche would have us believe that their cars defy the natural laws of physics and engineering, subscribing to an elite set of scientific principles exclusively. Sadly, they are simply machines and must dwell in the same kingdom as other more lowly but equally obedient machines. BTW I must humbly apologize for hijacking this thread from the harmfulness of 91 octane to "Will the ECU automatically compensate for this, and what is the implication?" I mistakenly thought I read this in the original post. Lee |
RE: 91 vs 93 octane
Hi Folks,
I run a BMW M3 and 996TT on 98 octane in Sydney and they work a treat and I also notice overall better economy and consistent performance. We have Shell, BP selling 98 octane unleaded, although recently Shell have put ethenol in their Optimax, hence I have moved to BP 98 unleaded. At the moment we pay $1.35 AUS per litre of 98 unleaded, lower octane full is available 91/95 but the overall cost of the 98 is worth it. Scott |
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