DIM Electronic Advance Ignition

Dan,

I doubt, the secondary current or voltage will change significantly from the HEI. The dwell control might be improved, however I think the HEI does a respectable job with that. The dwell time can be selected, however at high RPM, it is a matter of available dwell time, and time for the ignition event. That is a reason why coil on plug is better. The /6 has the advantage of less cylinders and typically less RPM requirement than a V8.

The major improvement will be the accuracy, repeatability and the ability to tune without mechanical adjustments. The base timing will still be manual, with a timing light on balancer at idle. Gone will be centrifugal advance, vacuum dashpot and other related components.

Timing is done with two simple tables. The RPM table has 10 data points in equal positions from idle to maximum RPM. The idle speed and maximum, are chosen depending on engine requirements. At each RPM point in table, a corresponding timing value is set. The ECU measures RPM, and in a linear fashion, interpolates values in between the data points. The timing based on vacuum is similar.

I typically work with 3D tables for engine management, the 3D table could be 10 x 10 or 100 cells to fill. For most this is too intimidating. By using the two 2D tables, the mindset tuning conventional distributors stays the same. Since vacuum is near zero at WOT, and closed throttle much of the possible information in a 3D table is non-germane.

The mechanical timing advance mechanisms are fairly crude. There can be friction, looseness, hysteresis, induced vibration and bouncing at stops. The vacuum advance mechanism also has faults of friction, hysteresis, wear and non-linear travel vs vacuum. I find it amazing that they in general work as well as they do. What is hard to do is make adjustments, test and make more adjustments. With the electronic system, change and test is easy!

The electronic pressure (vacuum) sensor is quite accurate and temperature compensated. The ability to measure RPM is also accurate, based on a clock with a quartz crystal. So, the ignition will be more accurate, predictable and easily tuned.