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Posting-Version: version B 2.10.2 9/18/84; site bonnie.UUCP
Path: utzoo!watmath!clyde!bonnie!wjh
From: wjh@bonnie.UUCP (Bill Hery)
Newsgroups: net.auto
Subject: Re: mileage and performance with hi-octane gasoline
Message-ID: <559@bonnie.UUCP>
Date: Mon, 16-Sep-85 13:32:05 EDT
Article-I.D.: bonnie.559
Posted: Mon Sep 16 13:32:05 1985
Date-Received: Tue, 17-Sep-85 05:11:53 EDT
References: <610@osu-eddie.UUCP>
Organization: AT&T Bell Laboratories, Whippany NJ
Lines: 21

> 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?
>

High octane gasoline does NOT have more energy per gallon than regular--
it only has more anti-knocking additives per gallon.  If your car does not
knock on regular, high octane should not improve your gas mileage. 
(If your car knocks significantly on regular, it is not burning the
gas efficiently, so high octane will improve mileage.)

Several years ago, I thought as you do and tried an experiment with a new
car (Plymoth Barracuda, 318 engine, 3 speed stick).  For the first 4 or
5 thousand miles, I used regular, then switched to premium for another few
thousand miles, then back to regular.  I found no real increase in gas mileage 
with high octane.


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