Date: Thu, 27 Jan 2000 22:04:09 GMT From: "Philip Hult" <hultnopsamdu> Subject: Re: Regular or Premium in 2.3T?
SAAB engines are high compression (howelse do you get 100Hp/ltr displacement?) The higher octane gasolines are more stable at these higher pressures. A lower octane gasoline as less stable and is more likely to ignite prior to the spark firing. This is why adjusting the timing can allow high compression engines to run smoothly (aka not "knock"). Also older cars with worn valves, or generally poorer compression will see less effect from the switch from 93 to 87 octane. However a car that was designed to run properly at 87 octane will _NOT_ show any real improvement in performance.with a higher octane fuel. It is unfortunate, however, that oil companies have convinced us consumers that there is more "power" in higher octane fuels. (They actually have roughly the same btu's/gallon, but simply different ignition temp/pres.) This mispreception has allowed oil companies to charge more for a product which is no more sparce, and nearly the same cost. My final words. I put premium (92 octane) into my 9000 2.0l turbo, and I pay extra for it. I hate the fact that I have to pay extra for it but it was what my engine was designed to run _most_effeciently_ with. I do also notice an improved mpg, and performance edge. my $0.24. Philip Four Weis <mweinopsamcom> wrote in message news:388DA4AB.7640B3A7nopsamcom... > Bill Hays wrote: > > > I've had the same experience as Julie, also in a '91 9000 2.3l turbo -- > > lesser grades (below 92 octane) won't ping or knock, thanks to the > > anti-knock circuitry, but my gas mileage with, say, 89 octane (I've never > > tried 87 octane) is about 2-3 mpg less in my daily driving (a mix of > > neighborhood, densely urban and freeway driving in the Seattle area) and > > noticeably reduced performance. The 2-3 mpg decrease in mileage offsets > > any price gain (about $0.10 to $0.15 per gallon) from the lower octane > > fuel. The lesson: stay with the premium gas -- better mileage, better > > performance, lower cost per gallon. > > I have a Saab and a Volvo turbo and my experience has been the same as Bill. I > get more miles per gallon with premium, enough to make it less expensive per > mile. Don't fall into the trap of only looking at the price per gallon, look into > the cost per mile. > > The anti-knock computer controlled system works by retarding the timing. Does > anyone have any knowledge about the effect on power output from retarding the > timing? Judging from the decrease in mileage, there is some relationship. >
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