Date:         Wed, 2 Jan 2002 08:58:07 -0500
Reply-To:     Angus Gordon <agordon@BRIGHT.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Angus Gordon <agordon@BRIGHT.NET>
Subject:      Re: B. Bobs day at the dyno and the importance of fuel air ratio
              update
Comments: cc: John Rodgers <jhrodgers@MINDSPRING.COM>
In-Reply-To:  <3C3292CA.9FFD2175@mindspring.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

John,
         I believe there are enough differences between the aviation and
automotive applications that EGT (exhaust gas temperature) is not a valid
method of setting the mixture on a car engine. Remember that in an aircraft
EGT is only a valid measurement for leaning purposes when compared to peak
EGT for that specific power setting. That works fine in an aircraft, where
you can set the power, lean to determine peak EGT in the leanest cylinder,
then set the mixture relative to that cylinder's peak EGT. I don't know how
you could accomplish that with the constantly changing power on the road.

As to burning valves, many piston aircraft engines are designed to run at
peak EGT or on the lean side of peak EGT in cruise. Exhaust gas temperature
is used as a relative measurement again, not an absolute in these cases.
The only limitations I know of in terms of specific EGT, are for
turbocharged engines, where TIT (turbine inlet temperature) becomes a
factor. Even in the waterboxer I think there'd have to be some other
ingredient to burn a valve, i.e. incorrect valve lash, overheating etc.

But, if someone wants the very best in EGT instrumentation (and CHT on the
same gauge) here it is -

http://www.insightavionics.com/pages/602.html


John Rodgers wrote:
>I've been away from aviation for quite a number of  years but I remember
>using the EGT gages as a guide to manually setting  the fuel air mixture
>during various flight regimes for best performance. On those aircraft with
>engines equipped with an EGT probe mounted in each exhaust stack just
>outside the cylinder head, it was possible to  select through each
>cylinder and determine which cylinder was running the leanest. The leanest
>running cylinder then became the guide cylinder by which the mixture for
>the engine was set. That way one avoided burning up a valve or worse,
>burning up the engine. By watching the EGT gage, for any given throttle
>setting (manifold pressure setting) the mixture could be set for Rich Best
>Power, Peak Power, or Lean Best Power...



Angus


================================
Angus Gordon                       '89 Carat
NW Ohio                            '86 Syncro