Bill,
My experience with dyno tuning is that peak power is found somewhere
around 12 to 12.5-1 A/F ratio. The 14.7-1 you mention has to do with
smog related issues. That is where engines are controlled to give the
best emission readings of the three gasses of concern, HC, CO & NOx. And
that really only happens with closed loop, cruise or steady throttle
conditions.
Tom, Redding CA (my engine goes on the dyno today) - #216 D/GCC
Bill Bennett wrote:
>
> 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
> >
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