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From: gvcormack@watdaisy.UUCP (Gordon V. Cormack)
Newsgroups: net.auto
Subject: Re: mileage and performance with hi-octane gasoline
Message-ID: <7414@watdaisy.UUCP>
Date: Mon, 16-Sep-85 18:48:34 EDT
Article-I.D.: watdaisy.7414
Posted: Mon Sep 16 18:48:34 1985
Date-Received: Tue, 17-Sep-85 05:10:48 EDT
References: <610@osu-eddie.UUCP>
Organization: U of Waterloo, Ontario
Lines: 34

> High-octane gasoline contains more energy per gallon than low-octane gas,
> right?  I mean, it accelerates better, hesitates less, and knocks very
> little on Super Unleaded as compared to driving on Regular Unleaded.  So a
> gallon of it should drive my car further (more mpg) than would low-octane
> gas, right?  How much further?  Enough further to offset the price
> difference?  What factors work into the equation?  Do I need to be able to
> change the mixture setting, compression, spark advance, or whatever, to make
> a difference?  Will the higher temperatures hurt my engine at all?
> -- 
> Human:	   Bob Sutterfield
> 	   Facilities Management Division

High octane gasoline will have no effect on an engine that
runs correctly with lower octane gas.  Every new-car owner's manual
I have ever read makes this perfectly clear.

If you are prepared to make engine mods, you can indeed get better
performance from higher octane gas.  The amount of power produced
by your engine is roughly proportional to the compression ratio.
If you switch from regular to premium, you may be able to use a
compression ratio of, say, 10.5:1 instead of 9.0:1.  This will give
you more energy for the same amount of gas.

Of less signigicance are some other changes that one may make.  With
higher octane gas, it is possible to run an engine slightly leaner
without pinging, and it is sometimes possible to advance the ignition
timing, which may improve performance.

Buy the cheapest gas you can, so long as your engine does not knock.
I don't think that any of the above mods, particularly timing and
mixture, could possibly recoup the difference in cost. 
-- 
Gordon V. Cormack      CS Department, University of Waterloo
   gvcormack@watdaisy.uucp     gvcormack%watdaisy@waterloo.csnet