Miata Mailing List: December 1993, Message #232
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   From: Andy Poling 
Subject: Re: gasoleeeeen
   Date: Fri, 24 Dec 1993 17:26:39 -0500

On Thu, 23 Dec 1993, Will Zehring wrote:
> Joining the "I'm no engineer" chorus, I always thought that one of
> the principal reasons for lower mileage in the winter is that cold
> air mixed with cold fuel just doesn't burn as efficiently as the
> warm stuff does.  This goes double for the cold start (i.e. cold
> head, cold induction, cold pistons, cold everything!).  So, to get
> a certain level of power more fuel has to be shoved in because a
> lower % of that fuel actually burns (hence nasty emissions must be
> much higher too, and not just because the catalytic converter isn't
> hot yet).  As the engine warms up the mixture is leaned down via the
> automatic choke.  In warm weather this leaning down occurs many
> miles (minutes) sooner.

True but this only applies to cold starting.  The problem during a cold
start is difficulty getting the fuel finely and evenly atomized in the
combustion chamber.  This is even worse in a TBI (throttle-body-injection)
or carb'ed engine - some of the fuel will actually "fall" out of the air
while in the intake manifold... 

-Andy (C/S Miata - Team Wannabee)

Andy Poling                              Internet: andy@jhunix.hcf.jhu.edu
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