Does the Marelli cap have 2 coil terminals ?

 

Yup!

 

So Marelli has 2 coils and 2 cap terminals and Lucas has 1 coil and 1 cap terminal, correct?

 

Basically correct although there was some use of primary and secondary coils in Lucas systems and also some single socket dist.caps had a vent spigot sometimes confused with second coil socket.

 

The Lucas system did sometimes have two coils, but oddly enough only one was connected with a HT lead to the distributor! Apparently modern coils are much better and Lucas cars no longer need the second coil.

 

AS I understand it (and I am open to correction) The full story is:
The Lucas as fitted to the HE V12 had TWO separate coils. One by the capstan tower and one in front of the radiator on the valance. They were wired in parallel (ie + to +; - to -) as, at the time, no coil existed that could reliably run a V12 at higher revs. The two coils in parallel effectively halved the load on each, and doubled the time available for the coil to recharge and produce a spark. If you disconnect the coil at the front of a Lucas car, the engine will misfire above 2,500 to 3,000 revs

The Marelli actually has a SINGLE coil, as by this time a single coil existed that could run a V12 at higher revs. BUT the coil has TWO output leads to the dizzy cap. This is because the rotor and HT to spark plug posts within the Marelli dizzy is a two-level affair. One level runs one bank and one the other. This is why a partial dizzy/rotor failure shuts down one bank of a Marelli car completely. BUT it does NOT shut down the injectors if the ignition fails in this way. Hence the possibility of a "Marelli fire" as unburnt fuel is sent through the cylinders on one entire bank into the red hot cat.
If your Marelli car suddenly loses power, you MUST turn off the engine!
Finally, a Lucas ignition car can be run with a single modern Marelli-type coil, as they are (as in the Marelli ignition) capable of firing the V12 at high revs.
Greg

 

The Marelli has 2 separate coils one runs each bank of 6. It is basically 2 separate ignition systems with a single 2 plane distributor.

The reason Lucas cars had 2 coils with only the primarys paralleled is because of charging time.

To charge a coil fully requires 5 time constants, one time constant is T = L / R, where T is time in seconds, L is the coil inductance and R is the coil resistance so by paralleling the coils the ignition amp will charge the coil quicker.

The secondary does not need to be connected.

The misfire in a Lucas with 1 coil disconnected is because the coil is not charged enough in the short time between ignition events to produce enough secondary voltage. This is also know as ignition dwell.

 

The Marelli system basically has two of everything working independantly apart for dizzy cap and ECU