[wolke9]

I tried searching the board . . .but couldn't find any definitive answer.

I know that BMW and its owners manual suggests 93 octane, but does anybody know if the engine has an anti-knock sensor for octane ratings below 93 octane? Will the car still run fine at reduced efficiency and power under 87 octane?? Just trying to figure this out due to the price of gas recently. . . .

I know that it will run at top performance with 93, but all of the vehicles that I've had also burn the 93 octane faster resulting in more frequent fill-ups at the gas station. If I could afford it, I would put in 96 octane that I used at a track one time. What a noticable difference that was!--even though it was only in a Honda

[F32Fleet]

91-93 makes no real difference. Hell, you can even run 89 w/out much of a problem (ie, easy on rpms and not super hot outside.)

[ward]

as long as the knock sensor is working the car will just retard the timing a bit to reduce power.

you're not going to see any better mileage with lower octane.

The big question is

What are you going to do with the $140 you save over the course of a year????????

[fredtoo]

Originally Posted by ward

The big question is

What are you going to do with the $140 you save over the course of a year????????

Booze and Strippers!

[puck724]

im going to jersey!! thats some cheap booze and strippers.

[fredtoo]

Originally Posted by puck724

im going to jersey!! thats some cheap booze and strippers.

I never saw what the big attraction to California was

[wolke9]

Originally Posted by fredtoo

Booze and Strippers!

Does this apply to women too? I was asking this question for a female co-worker (and also for my personal knowledge). I'm coming up with $175/yr savings on average!. . .that's enough for 1.5 strippers! or 1 hot stripper and 1 ugly one!!

[fredtoo]

If she is a stripper, I would guess that she could afford premium

[ON325i]

$140 can get yourself some very nice BMW accessories.

[lux.sh]

Just get 92octane and add toluene in the gas tank to raise up the octane rating if you want 96, 100, whatever.

in my personal opinion, just put in 92(or higher) that all gas stations provide.

[Xens]

Originally Posted by wolke9

Does this apply to women too? I was asking this question for a female co-worker (and also for my personal knowledge). I'm coming up with $175/yr savings on average!. . .that's enough for 1.5 strippers! or 1 hot stripper and 1 ugly one!!

Giggity giggity giggity ~~~

[Tater]

Originally Posted by Xens

Giggity giggity giggity ~~~

Sweet reference.

[afocoryw20]

It's not a problem to put octane booster in your fuel? How about regularly?

[spitfire6000]

dont forget to also put some sugar in the fuel tank with the gas. Makes the engine run like butter

[afocoryw20]

Originally Posted by spitfire6000

dont forget to also put some sugar in the fuel tank with the gas. Makes the engine run like butter

Thanks for the tip!!!! I just put some in and it runs like a champ What kind do you recomend? Brown, White, powdered, or condensed?

[cannonspike22]

Originally Posted by afocoryw20

Thanks for the tip!!!! I just put some in and it runs like a champ What kind do you recomend? Brown, White, powdered, or condensed?

heh, hell just mix all of em if you like

[shimshimhada]

It's better not to risk the long-term detrimental effects that may occur later. I put nothing lower than 93AKI in my car.

[ABR]

Regular gas or premium?
Can you use the cheap(er) stuff?

Your guide to choosing octane


GERRY MALLOY
SPECIAL TO THE TORONTO STAR

With the price of crude hovering at $60 (U.S.) a barrel and gasoline flirting with the dollar-a-litre threshold, the cost of driving is becoming more prohibitive by the day.

High fuel prices are here to stay. Inevitably, there will be some up and down price movement, but the long-term trend is consistently upward.

So what's a driver to do? For most of us, there are only three ways to reduce fuel costs: improve our driving habits; reduce the amount we drive; or switch to a more fuel-efficient vehicle.

If you drive one of the estimated 5 to 10 per cent of vehicles that use premium fuel, however, you might have another option. You might consider switching to regular fuel.

The temptation is great, for it could save you from $5 to $8 on every fill-up, depending on the size of your tank. But what will be the consequences?

There's a good chance they will be minimal, though it's not a sure thing.

Premium gasoline is recommended or required in some vehicles solely because of its octane rating. In fact, a premium gasoline is defined by its "octane rating," or Anti-Knock Index (AKI), which in Canada is typically 91 or more, and it must be clearly marked on the gas pump.

Knock is a tendency for the fuel-air mixture in a cylinder to auto-ignite, ahead of the flame-front initiated by the spark-plug. The result is an uncontrolled explosion that can, in extreme cases, break piston rings, or even pistons or connecting rods.

It's to be avoided, whatever the cost.

The AKI is the average of two different ratings, MON (Motor Octane Number) and RON (Research Octane Number), determined by laboratory testing in a sophisticated single-cylinder engine with a variable compression ratio.

Experimentation long ago determined that a chemical compound called isooctane was highly resistant to knock, so it was adopted by the industry as a reference fuel for comparing the knock resistance of gasoline blends in the laboratory engine — thus establishing their octane rating. A 91-octane gasoline provides the same level of knock resistance as a fuel comprised of 91 per cent isooctane and 9 per cent n-heptane.

Higher-performance engines with higher compression ratios or turbo/superchargers are inherently more prone to knock.

That tendency can be reduced by retarding the spark-timing — which also reduces performance — or by using higher-octane fuel.

That is why premium gasoline is often specified for use in those engines. Before modern electronics entered the picture, you had no choice unless you were prepared to risk serious damage to your high-performance engine.

But now that scenario has changed.

Other factors, including a buildup of engine deposits, can increase an engine's tendency to knock as it ages.

To compensate for that tendency, as well as to provide a fail-safe for turbocharged engines, manufacturers began installing electronic knock sensors on some engines.

They are now standard equipment on virtually all engines.

Those sensors determine the onset of knock from vibrations in the engine block, and send a message to the engine control computer. It, in turn, retards the spark timing just enough for the knocking to stop.

That system doesn't know or care what causes the knock — whether it is a carbon buildup in the combustion chamber or low-octane fuel. It protects the engine either way.

Which is why you may be able to use regular fuel in an engine for which premium is specified. In most circumstances, the knock sensor will provide adequate compensation, albeit at the expense of some flat-out performance.

In some extreme cases, such as trailer-towing, ascending steep hills, full-throttle accelerations, or carrying heavy loads, that compensation may not be enough and knock may still occur.

Ditto if the engine has already accumulated significant deposits in the combustion chambers.

A key consideration in deciding whether or not to try regular fuel is the precise wording in the vehicle's owner's manual.

If it says premium fuel "recommended," there is probably little risk involved. The company is recommending premium fuel to achieve maximum performance.

If, however, it says premium fuel "required," or "use only premium fuel," it is more than just advice and you should comply.

If you do wish to experiment, in a premium-fuel-recommended vehicle, you might try using a mid-grade (89 AKI) gasoline to test the waters.

Run through one tank driving easily to ensure that only the lower-octane fuel remains. Then, on the second tankful, try a full-throttle acceleration from 50 km/h or so, on an uphill grade if possible.

Listen carefully. If you hear a light "tinkling" or "pinging" sound from the engine, the experiment failed. Switch back to premium.

If not, take the next step and repeat the experiment on regular gasoline.

If no knock occurs, and if the acceleration you experience is sufficient for your needs, you are probably okay to continue and save yourself some money.

A couple of qualifications. On occasions when you know you will be towing, carrying a heavy load or driving in mountainous terrain, it would be good insurance to switch back to premium.

And if your vehicle is more than 10 years old, it may not have a knock sensor. So none of the above applies.

Caveat emptor!

[RedStripe]

Great read, thanks for the post!

[stressdoc]

The latest (November) Roundel has a nice article on gas. I worry that those of us in states where it is very difficult to find anything better than 91 octane are often running into problems with the pre-emptive knock sensors retarding the spark timing. This could account for the power variation problems that AudiA4 was complaining about.

[epiphone3]

A big thing that has been left out here is the fact that Premium fuels have special cleaning additives and such as well! Long term, always better to use premium... protect your investment and don't nickle and dime a BMW.

By the way, with the learning computers in BMWs, if you keep your driving habits consistant, you should actually get better fuel economy with premium fuel as the computer will advance timing as Octane Number increases... increasing the efficiency/completeness of combustion.