91 vs 93 octane
#11
02-17-2007, 02:29 AM
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...
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
#12
02-17-2007, 07:51 PM
RE: 91 vs 93 octane
ORIGINAL: rarctor
9200? Nah, try closer to 10,400. Our place in Breckenridge is at 9600, and we routinley go over 11 k (Eisenhower Tunnel, on I70
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)
Even new cars lose a lot of power at that altitude. My wife's '06 Bimmer does OK on the approach to the tunnel, but
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
ORIGINAL: ladams1
For the atlitudes cars go incluidng Leadville at 9200 feet the cars electronics can handle this.
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.
#13
03-05-2007, 01:28 AM
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.
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.
Wee!! Haven't had a chance to try it up in the mountains though - the weather's been kind of messy up there. I probably won't take it up there until after Memorial Day, anyway - they sand the snot out of the roads up in the high country, and the sand they use seems to be 1 part sand, one part pea gravel. Clear bras are an absolute necessity. My wife's 10 month old Bimmer already has a big crack in the windshield.. we decided not to replace it until May, since it's still perfectly fine to drive, and if we replace it now we could just as easily need to replace it again in May.
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
#15
04-03-2007, 04:00 PM
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.
"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.
#16
04-04-2007, 10:20 AM
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.
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.
#17
04-04-2007, 06:35 PM
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
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
#18
04-05-2007, 10:33 AM
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.
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.
#19
04-13-2007, 09:10 PM
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.
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
#20
04-19-2007, 11:17 AM
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
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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