Pressure Control Of Spark Timing

The distributor centrifugal advance mechanism provides a spark timing which over advances when turbocharger operates at high load. To counteract this, the distributor vacuum advance unit has a double function.

Under normal operating conditions it can advance the spark by a maximum 15°. At high pressures it retards the spark timing by 8° when compressor pressure reaches 5 psi (.35 kg/cm² ).