Date: Sat, 7 Apr 2007 10:08:31 +0100
From: "DervMan" <>
Subject: Re: Octane ratings.....what's the truth?

"Mick x" <> wrote in message > 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? > > > Check the above link out - is fairly imformative Well, kind of, it shows that an engine with the relevant sensors can handle higher octane fuel. I didn't see any mention of the handbook of the M3 saying something like "maximum power on 95 RON xxx bhp, maximum power on 97 RON, 360 bhp..." Because they *do* say that... -- The DervMan

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