Maximum advance

[Axel Rietschin]

> It would seem from the discussion below that coming up with an appropriate
> model is absolutely essential!  I can't get one hour on a dyno, much less
> pay to train a couple of people to help me.

Well... maybe there is just too many unknowns to come up with something of
any practical use.

> > With a copper pipe bolted on the head and connected to a "stethoscope"
on
> the other end, across a fully soundproof wall, you will hear >even
isolated,
> spurious knock bursts and be able to back off timing very quickly. For
this
> process to work well you need to stabilize the >engine at every load/rpm
> points and adjust them individually, and you need silence and
concentration.
>
> Why copper?

Probably because it resists heats, is easy to work with, is readily
available, transmits sound, whathever. All I know is it works well.

> I've read that the ping is actually ultrasonic and that what is heard is a
> subharmonic of the signal.  Did you see that on the scope?

No. The scope was useless but I admit we didn't really insist. My main point
was knock is relatively easy to hear but extremely hard if not impossible to
detect electronically past a certain engine speed, at least with traditional
techniques.

> Can I guess that your method would be only for one barometric pressure and
> one octane level.  If so, how do you compensate for changing atmosphere
and
> gas?  Is that the 2 degree bake off?

I have to say it is not "my" method, all engines are mapped this way. You
don't really "compensate" for octane rating, you actually map for it, it is
the main variable affecting your ignition map on a particular engine. In my
experience barometric pressure can be totally ignored. MAF and MAP systems
don't really need it at all, only Alpha-N systems will benefit from knowing
the ambiant pressure.

The two-three degrees back off are to stay safely away from the knock limit,
this will of course accomodate small variations in fuel octane rating and
operating conditions but ECUs have explicit ignition advance compensations
depending on air charge temperature and engine coolant temperature, at
least.

--Axel


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