Long-term effects of using < 91 octane fuel
03-26-2010, 01:56 PM
#31
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My Ride: SOLD...Jet Black 2008 550i M Sport with SAT, black interior. RPI exhaust and air scoop, 35% huper optik tint all around, CF roundels, flat black kidneys, Springfield Armory XD-40 jet black in glove box, charcoal filter removed.
Really?!! That's the reason gas prices go up?
I am not saying I am willing to pay $3 to $5 more for the same exact thing. I am just saying that the difference between putting in regular or premium gas is about $3 to $5 per tank. Not enough in my mind to justify the saving.
I am not saying I am willing to pay $3 to $5 more for the same exact thing. I am just saying that the difference between putting in regular or premium gas is about $3 to $5 per tank. Not enough in my mind to justify the saving.
yeah, really
03-27-2010, 12:09 PM
#32
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I live in IL. price difference between 87 and 93 octane fuel is .30c per gallon. I am getting about 330 miles per fuel tank on average. That gives about 45 fill ups a Year with average 15K miles per year. Usually it will be about 16 gallons of fuel per fill up. 16 gallons times 0.3c is $4.80 let's say $5 even. At 45 fill ups it comes to $225 a year, and that is with driving 15K miles per year! Don't we have a bigger problems to worry about? 
Just use the right fuel. It won't hurt.
Just use the right fuel. It won't hurt.
03-27-2010, 04:07 PM
#33
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I come from the MDX Board and the question of 87 vs. 91 octane has been debated ad nausea.
I will try to summarize:
Octane is a measure of pre-detonation. The higher the octane the greater the compression of the fuel before pre-ignition, i.e. knock.
Thus by using higher octane in an engine designed for higher octane you will obtain more power.
Now the real question is: ?When will you use that extra power?. Examples are racing, flooring your car at a stop light and towing (applicable to the MDX but not to the 5 series BMW).
Testing, using a dynameter, shows about a 7% decrease in maximum horsepower using 87 vs. 91.
But keep in mind that at 70 mph more than 50% of your horsepower is used over coming wind resistance. You are using between 50 and 70 horsepower, so it will not make any difference whether you use 87 vs. 91.
Other ?wives tales?;
You will get better mileage using 91 vs. 87. Not true. You will get more horsepower but not better mileage.
Your engine will run ?cleaner? using 91 vs. 87. Not true. The detergents in both are identical.
You will void your warranty. Not true. Electronic knock control will retard the spark to avoid knocking.
Also keep in mind, that in western states, Colorado for example, the highest octane available is 89!
One final caveat: You will do no harm using 91 octane other than to your wallet.
At 15,000 miles per year, 18 mpg average that is 833 gallons per year. At a price difference of $.30 a gallon, that is $1,000 extra after only four years.
To me it is simple: I would rather have $1,000 than Exxon Mobile, so I use regular and use regular in my Boxster and in my prior cars: 1997 BMW 745Li, 2000 and 2002 Boxster, 2004 Audi 8L and my 2006 BMW Z4, all with no ill effect.
JeffK
I will try to summarize:
Octane is a measure of pre-detonation. The higher the octane the greater the compression of the fuel before pre-ignition, i.e. knock.
Thus by using higher octane in an engine designed for higher octane you will obtain more power.
Now the real question is: ?When will you use that extra power?. Examples are racing, flooring your car at a stop light and towing (applicable to the MDX but not to the 5 series BMW).
Testing, using a dynameter, shows about a 7% decrease in maximum horsepower using 87 vs. 91.
But keep in mind that at 70 mph more than 50% of your horsepower is used over coming wind resistance. You are using between 50 and 70 horsepower, so it will not make any difference whether you use 87 vs. 91.
Other ?wives tales?;
You will get better mileage using 91 vs. 87. Not true. You will get more horsepower but not better mileage.
Your engine will run ?cleaner? using 91 vs. 87. Not true. The detergents in both are identical.
You will void your warranty. Not true. Electronic knock control will retard the spark to avoid knocking.
Also keep in mind, that in western states, Colorado for example, the highest octane available is 89!
One final caveat: You will do no harm using 91 octane other than to your wallet.
At 15,000 miles per year, 18 mpg average that is 833 gallons per year. At a price difference of $.30 a gallon, that is $1,000 extra after only four years.
To me it is simple: I would rather have $1,000 than Exxon Mobile, so I use regular and use regular in my Boxster and in my prior cars: 1997 BMW 745Li, 2000 and 2002 Boxster, 2004 Audi 8L and my 2006 BMW Z4, all with no ill effect.
JeffK
03-28-2010, 07:04 AM
#34
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Isn' t the highest speed limit in Bahama something like 35 mph? 
If one is driving lightly at slow speeds around town, low octane isn't really going to make a difference. Correct octane is needed for power delivery, hill ascent and safe engine operation under load. I may drive lightly around town, but I certainly want power when I need to get out of dangerous situations (merging, passing, etc).
Here's a tale of an engine incorrectly calibrated for lower octane:
A tale of low octane fuel, a grenaded Cadillac SRX and GM's response
If one is driving lightly at slow speeds around town, low octane isn't really going to make a difference. Correct octane is needed for power delivery, hill ascent and safe engine operation under load. I may drive lightly around town, but I certainly want power when I need to get out of dangerous situations (merging, passing, etc).
Here's a tale of an engine incorrectly calibrated for lower octane:
A tale of low octane fuel, a grenaded Cadillac SRX and GM's response
03-29-2010, 08:31 AM
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03-29-2010, 08:49 AM
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If you don't mind - please post a link to where I can find a written explanation that supports your dealer tech's claim. I would love to read it.
