Dave if you had your choice of EGT or oxygen sensor to tune by what
would you choose? Seems to me that maybe a combination of both would
be helpful especially if proper timing wasn't know. Also is it true
that peak power does not occur at a stoimeteric ration of 14.7:1 and
if not is it more toward the lean side?
Bill Bennett
----- Original Message -----
From: "dahlgren" <dahlgren@uconect.net>
To: "John Beckett" <landspeedracer@email.msn.com>
Cc: "Land Speed List" <land-speed@autox.team.net>
Sent: Sunday, September 10, 2000 9:11 PM
Subject: Re: exhaust
> Man did you ask a tough one.. to begin with EGT has little to do
with
> air fuel ratio if the timing is not known..the easy one is the probe
> ought to be about 1 1/2 to 2 inches from the port in an area that
will
> measure the average temp.. avoid the middle of bends especially..
Octane
> is compression ratio related so if low compression low octane and if
> picked right then the burn speed works out ok. A quick way to see if
the
> octane is too high is if you have an engine that wants a lot of
timing
> and the chamber and spark plug is not all that shrouded.. Then you
can
> run a timing value that is typical for the chamber design. If the
timing
> is correct a good number to shoot for is 1325 or so and under 1400
for a
> NA engine on gas...turbos can go to 1600 or more and nitrous if done
> right ought to be 1225 to 1300 but less than the temp without
it..the
> short version anyway in my mind.
> Dahlgren
>
> John Beckett wrote:
> >
> > Here's a little something I found in "Hot Rod" about exhaust.
> >
> > "During the combustion process, the leading-edge flame-front
> > temperatures may approach or exceed 2,500 degrees F, while exhaust
gas
> > temperatures measured in the header primary tube register
1,300-1,600
> > degrees F. Though many factors impact exhaust gas temperatures
(EGT), flame
> > speed and compression ratio are the dominant ones. As compression
ratio
> > diminishes, flame travel slows down and creates higher EGT
readings. This
> > occurs because the flame burns during blowdown and exits from the
exhaust
> > valve. Likewise, when ignition timing is retarded, the EGT
increases."
> >
> > So I have two questions: For racing is there one EGT reading
to indicate
> > the correct A/F ratio? Cause it looks like compression and timing
will
> > change the reading, but how much? And how far from the cylinder
head should
> > the probe be placed?
> >
> > John Beckett, LSR #79, E/FCC
>
|