Because the system uses a narrow band for closed loop operation, you will
want to tune around stoich as John noted. With the stock AFM and engine
controls, you are limited to this one strategy unless you run open loop all
the time in which case you'll be able to adjust it for a bit more power,
but your ability to control AF under varying conditions is EXTREMELY
limited.

We are going to be going to the dyno either this week or next to do some
LMU final tuning, we'll be sure to get the results out there for you.
Eventually we'll have EGT's, and cylinder pressures monitored, these are
important factors to consider in the tune as well. I would not recommend
shooting for a lean AF when tuning in general, especially on a motor that
is prone to hot spotting and blowing head gaskets like the boxer, but we
are going to be making an "official" determination on where we are going to
be running the LMU AF along with Bob at boston engine, and it might help
serve as a guideline for others as well.

Jim

At 08:27 PM 4/23/2006, John Bange wrote:
> >
> > Bentley wants us to adjust the AFM based on the CO content of the exhaust
> > gas
> > (not measured with the above unit).  So, does anyone have good data on
> > what the
> > air:fuel ratio is supposed to be?
> >
>
>For gasoline, perfect AFR (called the "stoiciometric" ratio) is 14.7:1. No
>engine achieves a perfect burn, though, so for "full throttle" the ECU goes
>fairly rich. According tho the Bosch Fuel Injection & Engine Management book
>(Probst), max power is at 12.6:1, best economy at 15.4:1. The EFI system
>tried to stay on the rich side of 14.7:1, but as close to it as possible.
>Generally when you tune with a wideband O2 sensor you aim for right around
>stoiciometric and from there the ECU can handle the fine tuning. So long as
>you get it into the ECU's effective self-adjustment range, the CO, NOx, and
>HC should take care of themselves.
>
>
>--
>John Bange
>'90 Vanagon - "Geldsauger"

________________________________________
Bostig Engineering
Engine Systems Voodoo
http://www.bostig.com/
617.272.3800
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