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Date: Wed, 4 Apr 2007 17:31:15 +0100
From: "DervMan" <>
Subject: Re: Octane ratings.....what's the truth?

"gerry" <> wrote in message >I know this is old stuff, but I would like some input (hopefully informed) > on current thinking, now that gas prices have skyrocketed and there is a > real financial significance that just didn't exist "in the olden days". > Here in British Columbia, Canada we are paying $1.17/litre in $Cdn or 1.17 > x > 3.785 (l. / U.S. gal) x .86/1=$3.80 U.S. / U.S. gallon.....and that's for > regular. Let's look at about $4.10+ U.S. / U.S. gallon. > The book for my car 2001 V70xc recommends a minimum octane (RON) of 91, > and > I see regulars at 87 and mid-range at 89. Then you should run it on the 91 stuff. Is that considered premium? In the UK we have a different scale, ordinary unleaded is 95 RON, super is 97 upwards. You can buy 102 RON. :) > I listen to Radio Station KGO (San > Francisco) at night and often hear their science Guru Bill Wattenberg (PhD > etc. etc. knows all, et al) who says, "If it will run on regular, use > regular. A modern sophisticated car engine may not run initially that > well, > but sensors will "re-tune" to the lower octane and will be > power effect on warranty. The theory, as I > understand it is that "higher octane" doesn't mean more "power" in the > gas, > it means elements added to adjust combustion rate. Hmm. Octane is the opposite of cetane in diesel. The higher the octane, the harder it is to get the fuel to burn when compressed - which means you can squeeze it harder for a bigger bang. A higher cetane rating in diesel means it will burn easier when compressed. > In his opinion higher > octanes are "generally speaking" a scam on automobile users perpetrated by > the oil companies and encouraged by the auto manufacturers. Ignore him and try it yourself. Generally, turbocharged cars like higher RON ratings, 'cos the fuel:air mixture can be squeezed harder before it detonates. Pre-detonation is A Very Bad Thing, also called pinking. Saab donks for the last X years, where X is many :) have had a knock sensor that adjusts the ignition and reduces power to avoid pinking. If you have a turbocharged Saab petrol engine and you run it on a lower RON fuel, it'll produce less power or damage itself. Run it on higher RON stuff and it'll produce the most it can, subject to tolerances / ignition curves. Not put especially scientifically... :) > What's the consensus? That Bill Wattenberg is an idiot? As Fred says, who cares? Suck it and see. But, if your handbook says 91 RON and you try 87 RON, you _may_ invalidate any warranty, but I don't know of a modern-ish donk that could damage itself like this, merely run like a three legged cat (i.e. lumpy and not as good as it should). :-) -- The DervMan

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