What fuel octane do you use?
12-25-2014, 03:25 PM
#16
Advanced
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.
...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.
12-26-2014, 03:08 PM
#18
Three Wheelin'
You could run 89 or less with an S or V6 (or any non-turbo application) with some side effects, but non overly harmful. You would not want to run anything less than 91 with a Turbo or FI car. You would lose a lot of power, have pretty bad fuel economy, and would likely put the car into limp mode. If you have no choice but to run less than 91 because of availability, or something, then keep a light foot on the gas and don't go WOT until you get a higher octane back into the tank.
12-26-2014, 03:22 PM
#19
Three Wheelin'
Same for a CTT. Having a Turbocharger is almost like having a variable Compression ratio. Drive easy and more like a relatively lower compression ratio (9.5:1) and as the Boost goes up so does the relative compression ratio, and the need for higher Octane.
12-26-2014, 10:42 PM
#20
Rennlist Member
Your engine's Motronics system with knock sensing will protect your engine from low octane fuel, but will cost you HP, especially at high air and operating temperatures.
Ethanol content, increasing from 0% to the 10% legal limit, does degrade mpg, although it tends to raise octane rating. Ethanol has substantially lower BTU/gal, and it is a lower density fuel, than pure gasoline. So you will get higher mpg with 100% gasoline rated 87 than you will with a 10% ethanol blend rated 93 octane. Plus, ethanol is much more perishable at normal temperatures than gasoline, but that is a separate issue.
So yes, if you are just cruising on a trip, using regular gas won't hurt your mpg, but you won't have rated HP if you hit it hard for a short burst. For daily driving around town and commuting where you like to frequently hit it hard, Premium ethanol blend is probably fine. If you don't care about all that power, but the lower octane. If on the other hand, you are doing some kind of speed event and maximum power is most important, buy the expensive premium gasoline with no ethanol but more aromatic content, which are higher density and higher higher BTU/gal and also have higher octane.
Got it?
12-27-2014, 01:45 PM
#21
Advanced
You could run 89 or less with an S or V6 (or any non-turbo application) with some side effects, but non overly harmful. You would not want to run anything less than 91 with a Turbo or FI car. You would lose a lot of power, have pretty bad fuel economy, and would likely put the car into limp mode. If you have no choice but to run less than 91 because of availability, or something, then keep a light foot on the gas and don't go WOT until you get a higher octane back into the tank.
A turbocharged car may be affected more by low octane gas, but as Mcbit points out, without doing dyno testing on the specific vehicle, we can only speculate how much. One big factor on octane requirements for a turborcharged vehicle is heat. The same vehicle that has to dial back boost and timing on a 100f day while running 91 octane could run full boost and timing advance on 87 octane when it is 30f.
12-27-2014, 09:26 PM
#22
Three Wheelin'
I'm not speculating. I've seen it a lot of times in logging various FI cars with ME7 code, including CTT's. But, you read somewhere online that it's OK, so not much info I can throw at you to change your mind.
01-02-2019, 06:16 PM
#24
85-87 is fine and I think if you did some testing and the math you will find that the trade-off in performance and mpg's really isn't worth it. As far as additive pack go's if you trust what the man tells you your a fool.
LOL
01-04-2019, 03:54 PM
#27
All gasoline fuels (ethanol blend or pure gas) produce PRECISELY THE SAME amount of energy per volume. The ONLY thing that changes is that lower octane fuels burn faster, higher octane fuels burn slower and that property is responsible for the resistance to pre-ignition (knock/ping). A gallon of regular has the same energy as a gallon of premium. A vehicle optimized to operate efficiently on regular fuel will NOT produce more power when running premium fuel.
At high altitude, everything operates at lower pressures even in turbos... turbos reduce power loss at high altitude, but as altitude increases, even turbo motors, lose the ability to maintain the same combustion chamber pressures -- and the pressure inside the combustion chamber is what dictates the need for premium fuels with higher octane. The higher the combustion chamber pressure, the higher the octane needs to be to resist pre-ignition. Note that knock/ping doesn't typically happen at minimum combustion chamber volumes, it happens when the piston approaches bottom dead center... the remaining fuel in the cylnder that had been burning at a controlled rate suddenly reaches a combination of temperature and pressure inside the cylinder that the remaining fuel near bottom dead center explodes spontaneously, driving the connecting rod hard into the crank bearing surface and that force is transferred along the length of the crankshaft. The pressure in the cylinder is actually higher as the piston approaches bottom dead center than it is inside the combustion chamber before spark.
You WANT lower octane at higher altitudes. Higher octane fuels at high altitudes can result in the fuel burning so slowly (from lower internal pressures) that you don't burn all the fuel in each power stroke. (assuming the engines are typical "factory" engines, tuned for 0-2500 feet operation where most people live in the US).
Then there is the issue of the "additive package"... they are NOT particularly different for regular vs. premium. All cars today have electronic fuel injection so there is a need to have specific additives that resist clogging injectors (primarily). I am guessing with so many direct injection engines on the market, that some new additive will be required to combat carbon buildup on the "back sides" of valves. But there are ways to remove the carbon that are fairly easy. Now Chevron's additive package may be different than Exxon/Mobil's additive package, but you are talking about differences of fractions of a percent by volume. There might be 0.03 % of Additive 1 in Chevron fuel, 0.035 in Exxon/Mobil fuel and 0.025% in "generic fuel" dispensed at off-brand and discount stations. These differences are TINY TINY TINY and those tiny differences LEGALLY allow oil companies to tout the additives as being "better" than the additives in other fuels. The "additive package" is a big game with differences from the federal standards (all fuels must have federally mandated additives... the fuels can have MORE additives, but not less) being so small that there's no practical difference when used in any given vehicle. Besides, you can put a little Chevron Techron in premium fuel purchased at a discount gas station and you end up with fuel just as good as Chevron fuel for the cost of an ounce or two of Techron per fillup.
At high altitude, everything operates at lower pressures even in turbos... turbos reduce power loss at high altitude, but as altitude increases, even turbo motors, lose the ability to maintain the same combustion chamber pressures -- and the pressure inside the combustion chamber is what dictates the need for premium fuels with higher octane. The higher the combustion chamber pressure, the higher the octane needs to be to resist pre-ignition. Note that knock/ping doesn't typically happen at minimum combustion chamber volumes, it happens when the piston approaches bottom dead center... the remaining fuel in the cylnder that had been burning at a controlled rate suddenly reaches a combination of temperature and pressure inside the cylinder that the remaining fuel near bottom dead center explodes spontaneously, driving the connecting rod hard into the crank bearing surface and that force is transferred along the length of the crankshaft. The pressure in the cylinder is actually higher as the piston approaches bottom dead center than it is inside the combustion chamber before spark.
You WANT lower octane at higher altitudes. Higher octane fuels at high altitudes can result in the fuel burning so slowly (from lower internal pressures) that you don't burn all the fuel in each power stroke. (assuming the engines are typical "factory" engines, tuned for 0-2500 feet operation where most people live in the US).
Then there is the issue of the "additive package"... they are NOT particularly different for regular vs. premium. All cars today have electronic fuel injection so there is a need to have specific additives that resist clogging injectors (primarily). I am guessing with so many direct injection engines on the market, that some new additive will be required to combat carbon buildup on the "back sides" of valves. But there are ways to remove the carbon that are fairly easy. Now Chevron's additive package may be different than Exxon/Mobil's additive package, but you are talking about differences of fractions of a percent by volume. There might be 0.03 % of Additive 1 in Chevron fuel, 0.035 in Exxon/Mobil fuel and 0.025% in "generic fuel" dispensed at off-brand and discount stations. These differences are TINY TINY TINY and those tiny differences LEGALLY allow oil companies to tout the additives as being "better" than the additives in other fuels. The "additive package" is a big game with differences from the federal standards (all fuels must have federally mandated additives... the fuels can have MORE additives, but not less) being so small that there's no practical difference when used in any given vehicle. Besides, you can put a little Chevron Techron in premium fuel purchased at a discount gas station and you end up with fuel just as good as Chevron fuel for the cost of an ounce or two of Techron per fillup.
01-04-2019, 08:38 PM
#30
Burning Brakes
NIST has a standard for stuff like this, as summarized on this Wikipedia page:
https://en.wikipedia.org/wiki/Gasoli...lon_equivalent
Check out the table, for kWh / gal (that's energy per volume) for gasoline vs. Ethanol. Those numbers are something I can agree with: 33.41 for gasoline, 22.27 for Ethanol, which is close enough to 2/3 for me.
I always use the highest octane I can get at the pump for my Porsches and other cars that call for premium gas, which is now down to 91 here in the Democratic Peoples Republic of Kalifornia. I also put in Lucas fuel injector cleaner whenever I feel like it. Similar to why I put CeraTec in the oil - doesn't seem like it can hurt and it might help.