TCI and CDI both are improved technology of ignition system used by a different automobile company.  First of all, you should know the full form of these two terms. 

Full form of TCI - Transistorised Coil Ignition
Full form of CDI - Capacitor Discharge Ignition

The main difference between them is capacitor discharge ignition is when a capacitor stored energy is used for ignition while transistor controlled ignition is when the ignition coil current is driven by a transistor. 

Let us have a deep insight into the comparison between transistorised coil and capacitor discharge ignition. 

Difference between TCI and CDI :

  • CDI ignition system is independent on time while in TCI ignition system is dependent on time.
  • CDI Ignition makes the spark by discharging a capacitor loaded with high voltage about 200 to 450 volt from the ignition coil by using an SCR known Thyristor while TCI Ignition charges the coil with the current before the spark is done. Spark is done when the current is cut suddenly.
  • CDI coils have low impedance and inductance is about XL< 1 ohm and can reach high RPM makes high power and short sparks while TCI coils have high impedance is about XL >1 ohm and can reach lower RPM thus spark duration may be longer.