[Diy_efi] Ignition Timing

[Adam Wade]

--- "Becker, Damon (Damon)" <damonb at avaya.com> wrote:

> I suppose I'm advocating relying on the knock sensor
> as little as possible.

If your engine is knock-limited, then you want to
detect knock, either through an acoustic/piezo sensor
or ion sensing.  It's one hell of a lot easier than
trying to make a map to account for all possible
conditions on a turbo'd vehicle.

> I realize the OEMs do this, but my aftermarket EMS
> might not be capable of doing the same things as the
> OEM setup.

I'd seriously consider finding one that could take
input from a knock sensor, if you're using an engine
that is knock-limited.

> Besides, doesn't that amount to a band aide on a
> poorly-done mapping job?  

Huhwha?  Knock limiting is designed to get the most
power possible with low emissions, and is done almost
universally on car engines today.  You can't make any
more power from the engine that running at the knock
limit, unless you add water injection or change the
compression ratio (or lower the boost, or use a bigger
intercooler).

> As for the compensation maps, setting a map means
> holding all else constant and making measurements
> relative to that map.  Since that's difficult or
> impossible, you have to rely on theory and give a
> buffer.

If you're using a knock-limited engine, expect your
"conservative" map to lose a lot of power over running
on the verge of knock.  I wouldn't begin to be able to
suggest anything theory-wise that would allow a
computational-based (yet accurate) knock limit advance
curve for an automotive turbocharged app.

> So if the theory says 1 degree for ever 20 *C of
> intake charge, then give it 2 degrees and call it
> good?  

What about boost pressure?  Coolant temperature? 
You're going to have a great number of mpas all being
used together for the same calculations (or a number
of multi-dimensional matrices combining several of the
variables).  I would be pretty amazed if you could get
good power and stay out of knock usion theory-based
maps alone on a knock-limited turbo vehicle.  It's
much easier to do on a vehicle that isn't
knock-limited, as you're not having to try and
estimate where knock will occur; you're shooting for MBT.

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