Date: Fri, 06 Apr 2007 09:53:31 GMT
From: johannes <>
Subject: Re: Octane ratings.....what's the truth?

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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