Perhaps this may help some of us who may not fully understand the EST and ignition advance/timing!
EST = Electronic Spark Timing.
There is NO mechanical advancing mechanism within the ignition distributor.
There is also NO actual or physical spark advancing done by the module....
but read on before disagreeing!
**Since the laws of physics do not allow a remote electrical event to occur any sooner/earlier than when it was initiated, the EST system must incorporate
a delay of an advanced spark event via the module's electronics.
So..... the EST distributor's triggering event must produce the spark event at the total advance value. In other words, if the distributor was indexed for a working module, and if we were to take the module out of the equation, the triggering system would send out Full Advance, or very close to it, no matter what the RPM.
Going back to ** above:
The EST module creates a
delay of the spark event.
The EST module's
delay is greater at lower engine speeds, and the
delay is less as engine RPM increase.
If the engine must see a BASE advance of 8* to 10*, then the system's delay is at it's greatest value at low idle RPM.
The controller is progressively delaying a range of let's say 0* to 22* (32* TA minus a BASE of 10* = 22*).
In other words, if the engine requires a BASE advance of 10*, the controller is
delaying at it's MAX of 22*.
If the engine requires a TA of 32* at the Full In RPM, then the controller is now
delaying at it's minimum or zero.
Now the SBC Marine version:
The common SBC Marine engine is fitted with the non-ideal GM Full Dished pistons, of which makes this engine more prone to Marine Load/Ignition Induced Detonation.
The EST (and any other Marine ignition systems) are designed and adjusted to hold back the advance in order to avoid detonation.
The internal advance curve is rather steep....
1..... it is common to see 20-22 degree of timing at 1000 RPM on a V-8, maybe more with aftermarket modules.
2.... Max advance is usually seen at 2500 RPM.
1.... It's been my experience that BASE advance should be in the range of 8* to 10* BTDC......... much more, and starting becomes an issue. Once started up, it will handle a greater BASE value, and we will see an increase in RPM, but at 20*-22* it will "buck" during starting, and may not even start!
2.... Most SBC Marine engines want to see a Full In advance of approx 28* to 30* and no earlier than at/above 3,200 RPM.
Any sooner or any greater, puts the engine at risk of detonation damage.
If the advance curve continues beyond 3,200 RPM,
and remains linear, it is typically a non-issue.
I know that many shops set BASE advance, and do not look any further. I have never sent an engine away without having looked at both the progressive and the TA. In most cases all is ok.... but occasionally we will find one that is not correct!
Always refer to the OEM ignition advance curve for your engine model and serial number.
It would be a good idea to see if the system is actually delivering it.
.