The coil on the left is the old standby oil-filled coil. The coil on the right is a production HEI coil style. The HEI style is often referred to as E-core coils. They generally employ a larger magnet and are more efficient than older oil-filled coils. Religiously avoid contact with the oil in those old canister coils. The oil is dangerously carcinogenic so don’t use it as a salad dressing.