7747 spark control questions.

[rr]

Shannen, if you don't mind, I would like to add one more item to consider
when choosing the base (inital) timing. A v8 distributer is only good for
about 42 degrees of advance. This is a physical limitation.

By setting more base timing, more total crankshaft timing can be had. This can
be good for things like aluminum heads and hi-way spark. You have to
balance this added inital timing against hot cranking stubbornness.

BobR.


Shannen Durphey wrote:

> Programmer wrote:
> >
> > Ok, EST bypassed is non computer dizzy timing. You should then be at TDC or
> > 0 degrees as per the timing decal. If Bias warm is 10 deg. Bias
> > cold is 20 deg (I think). Winbin table for 50 Kpa @ 600 rpm is 29.88 deg
> > whereas
> > Tunercat is 20.1 degrees BTDC. (Using an ARJT as an example).
> > Winbin adds 10 deg or includes the bias--TC doesn't add it-- so what's the
> > actual "engine" measured timing value at 50Kpa and 600 RPM ? I'm assuming if
> > the WOT table has a negative, it's adding 10 bias. So lets' say we have a
> > negative 3 at 100Kpa and 1000 rpm--we've got an actual 7 BTDC at that point
> > provided we set the ignition timing as specified. If we add 9 degrees to our
> > base timing, we've then got a physically measured16 BTC at 100Kpa and 1000
> > rpm. Is this not correct ??
>
> If you add 9 degrees at the distributor and do not change any prom
> values, you've advanced the timing at the crank by nine degrees.  If
> your distributor is set at 9 degrees, and the value at 0x009 is 9
> degrees, the position of the distributor is adding no more timing to
> the ecm calculation.  The ECM calculates desired timing based on
> tables, warm n cold spark bias values.  Then the ECM subtracts the
> initial distributor setting from the final calculation to deliver the
> correct timing.
>
> Base timing, bypass timing, non EST timing (all the same) affects
> startup, specially hot, limp home driving, stall recovery, minimum air
> setting, dieseling (Yep, it can happen w/TBI).  Most of us set it -n-
> forget it.  The initial distributor value is a means to allow the base
> timing to be set at your choosing  The spark tables will reflect
> accurate timing.  You pick the timing value that you want, and the ecm
> takes care of remembering where the distributor base timing is so the
> timing at the engine is the timing you've set in the tables.
>
> So you can have 9 degrees advanced base timing, and nine degrees in
> static timing value in ecm, and they cancel each other out.
>
> Shannen
>
> >
> > Lyndon.

<snip>

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