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#1 (permalink) Old 07-31-2003, 10:35 AM
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http://www.usatoday.com/money/autos/2003-0...remiumgas_x.htm

Today's engines use highly evolved versions of a device called a knock sensor to adjust settings automatically for low-octane gas. And more engine control computers have adequate memory to allow separate sets of instructions for various octanes. The engine control computers keep pushing to maximize performance on whatever grade of fuel is used.

Extreme pressure inside the cylinders causes knock, which is the sound of the pistons literally rattling inside the cylinders. Too much too long can damage the engine. A little now and then won't.

The only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. "You're driving along and just tramp the gas and the knock sensor cannot sense the knock fast enough in some cases," because the supercharger boosts pressure so fast, says Bob Furey, chemist and fuels specialist at General Motors.

Burning regular when the owner's manual specifies premium won't void the warranty, nor damage the engine, even the most finicky automakers say. "You're giving up perhaps just a little bit of performance that a customer wouldn't really even notice, it's so slight," says Furey.

Automakers say they don't test premium engines on regular to check the difference, but some auto engineers estimate that power declines roughly 5%.

"We can't guarantee the vehicle will perform as specified if other than premium fuel is used," says Mercedes-Benz spokeswoman Michelle Murad. All U.S. Mercedes engines specify premium.

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#2 (permalink) Old 07-31-2003, 10:47 AM
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I dont know about just supercharged cars. High compression engines need it just the same, detonation is some pretty serious stuff. But all I know is that if an auto company reccomends premium that is what I am gonna run in it.

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#3 (permalink) Old 07-31-2003, 03:22 PM
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we had this debate at maxima.org for the 2004 max. basically stating the same thing. now if you were to go the N/A route with 15.1 compression or higher then of course you would need higher octane. all boosting will also require it.

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#4 (permalink) Old 07-31-2003, 03:31 PM
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frankly i would probabily used 89 octane in most cases.....on pretty much any car...my mom runs 89 on her volvo XC (turbo awd) and it runs fine. same on my sisters S40 and my dads 960 (which recommends premium)..but they would never run regular

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#5 (permalink) Old 07-31-2003, 04:20 PM
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Grain alcohol and a swizzle stick. But only the red swizzle sticks becausethe brown ones cause detonation. Everclear works best. But don't mix it with anything. And wear boots with thick socks, but no underwear because the static discharge could cause an explosion in your boots of a magnitude you've never seen before. And burn your pubies right off.


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#6 (permalink) Old 07-31-2003, 10:46 PM
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[


i use 93 or 94 octane , never anything below 91, i dont notice any difference between 91 and 94 however i do know and have the satisfaction that im using better gas, knocking will kill your engine in time, knock sensors help to a degree, mine is disengaged, (due to the performance chip programming)

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#7 (permalink) Old 08-02-2003, 10:51 AM
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what is knocking??

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#8 (permalink) Old 08-02-2003, 02:04 PM
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Detonation, which is also known as postignition, causes the fuel to burn too rapidly. A secondary flame results from spontaneous combustion due to compression and/or radiation and moves at supersonic speed. The two flames collide causing an explosion and the infamous "pinging" noise so familiar to us. (Note: The pinging noise is the result of the cylinder wall vibrating like a guitar string due to the explosion).

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#9 (permalink) Old 08-02-2003, 02:05 PM
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Preignition, like the name indicates, is the result of the air/fuel mixture burning too soon. It can easily cause the temperature to raise in excess of 4,000°F and the pressure to surpass 1,200 psi. Obviously, if not controlled, it can become "runaway preignition" and there won’t be much engine left.

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#10 (permalink) Old 08-02-2003, 02:05 PM
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these are both causes for the pinging noise which is referred to as knocking

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#11 (permalink) Old 08-03-2003, 11:44 AM
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I guess when the guy is saying that the supercharger is force-feeding fuel it means that he's force-feeding part of the fuel(the air portion) b/c a supercharger is designed to push more air not push more gas... that's the job of the injectors.
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#12 (permalink) Old 08-05-2003, 01:32 AM
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I have to use premium on my car. My motor doesn't have knock sensors and the chip I am using forces me to use at least 91. Hell my motor needed 91 even without the JC chip.

Detonation and pre-ignition are extremely similar. They are many times indistinguishable and each one can lead to the other.

Detonation happens when 2 flame fronts meet one another and cause extreme combustion chamber pressures... bad news to your motor

Pre-ignition happens when the air/fuel ignites before it should and basically acts like the timing is extremely advanced... very stressful on engine components as well.

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#13 (permalink) Old 09-27-2004, 08:42 PM
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Yes this is an old thread I am responding to, but I was told at the dealership that the octane may not affect the engine but it could affect the catalytic converter, leading to its early demise. Is this fact?
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#14 (permalink) Old 09-28-2004, 01:42 AM
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Talking

As far as I know, my '92 325i has no knock sensor.

I use 92 octane (the highest I can get here in Calgary, Canada) 10% Methanol Gasoline that Husky Gas Stations sell.

The gasohol helps year round, especially when it goes to -20 Fahrenheit or lower in the winters.

Even if lower octane fuels will work, I get the impression that the more highly refined high octane fuels are cleaner and better for the car to drive.

If lower octane fuels would work okay in my engine, I would still pay the extra to get that extra 5% (9 BHp) from my engine.
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#15 (permalink) Old 09-28-2004, 02:51 PM
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Quote:
Originally posted by BMWL2@Jul 31 2003, 07:47 AM
I dont know about just supercharged cars. High compression engines need it just the same, detonation is some pretty serious stuff. But all I know is that if an auto company reccomends premium that is what I am gonna run in it.
[snapback]27417[/snapback]

This isnt true. What the article is saying is that most modern cars have computers which change the ignition timing. Even with the compression at 15:1, which no modern cars have, that 15:1 is at top dead center. At half stroke the compression is 7:1, so if you ignite the fuel here by the time its finished burning it would be near TDC, so it wont knock. When the timing is advanced to beyond optimum point it wont knock, and optimum point is around 3/4th stroke. Everything this acticle says is 100% true.

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