Porsche 928 Workshop Manual page 521

928
Ignition System
28
The distributor for USA/Canada models has a vacuum unit for advance control beginning
with 1983 models.
IGNITION ADJUSTING AND TESTING VALUE
BEGINNING WITH 1983 MODELS
Ignition timing (without vacuum) 20' BTDC at 3000 rpm
Idle speed
Centrifugal control
(without vacuum)
Vacuum control (at idle speed)
650 f 50 rpm
4 to 8' BTDC at idle speed;
24 to 28" BTOC at 5000 rpm
Produce approx. 400 mbar
with manual vacwm pump
"Advance" 13 to 17O
Printed in Germany - VII. 1983
Ignition Adjusting and Testing Value,
28.29
1983 Models