rbohm":32c3t8xt said:
are we talking a carbed or an efi engine?
Either. We are talking about steady state cruze here.
rbohm":32c3t8xt said:
stoichiometric air/fuel ratio
That is the ideal balanced ratio. This however is not best for power so why would you expect it to be the best for cruze?
Through out the daily driving regimen the AF varies from richer then 14.7 to leaner then 14.7 it is only in the steady state driving that it reaches a constant value and as such the leaner you can make the mix while maitaining speed the better your gas milage will be.
Taken from manifold versis ported vacumn advance
:arrow:
viewtopic.php?f=1&t=63354
I did not write this article, it is written by a retired GM/Chrysler Engineer, goes by JohnZ on another forum.
As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word document if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative.
TIMING AND VACUUM ADVANCE 101
The most important concept to understand is
that lean mixtures, such as at idle and steady highway cruise,
take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency. :!:
Toyota a well recognized and respected manufactorer published in their sales broshures an emission chart that included a band for best economy centered around 16.1 AF. I believe them.
