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Date: Fri, 06 Apr 2007 13:58:57 +0100
From: Mick x <>
Subject: Re: Octane ratings.....what's the truth? Check the above link out - is fairly imformative Mickx On 6/4/07 10:53, in article, "johannes" <> wrote: > > > DervMan wrote: >> >> "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... :) > > I normally use Shell Optimax in my 1993 9000CSE 2.0 LPT, 131k miles, > but the station on my route was closed for 3 months, then I used Morrisson > supermarket fuel (regular only). The engine was OK but not sparkling, > there were occasional flat spots which I put down to maintenance, filters > etc. Recently changed back to Optimax, and it feels like the engine has > been 'cleaned up' as it runs smoother and more consistently. Apart high > Octane, quality fuels also contain cleaning agents. Exhaust systems used > to be something which lasted for 3 years or so, but I'm really surprised > that the exhaust hasn't failed for 6 or 7 years since a box was last time > replaced. Wonder if that may have something to do with better fuel quality?

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