The TDC Angle in the trigger setup tells the ECU where top dead center is relative to the trigger signal. You normally set it by locking the timing and matching the ECU's number to a timing light, as covered in how to set your TDC offset angle.
That single number is only exactly right at the RPM you set it. Trigger sensors and their signals have small delays, and a fixed delay in time becomes a bigger error in crank degrees the faster the engine spins. So an engine that's spot on at idle can show real timing drifting from what the ECU commands as RPM rises.
The TDC Offset Angle Table fixes this. It works over RPM, and whatever value it holds at a given engine speed is added to, or subtracted from, the TDC Angle. The result is that the ECU's timing and the timing at the crank agree across the whole rev range, not just at idle.
How we use it
- Set the main TDC Angle at idle with timing locked.
- With timing still locked, raise engine speed in steps and check the actual timing with a light at each step. How to use a timing light covers the technique.
- Where the light disagrees with the locked value, enter the difference in the table at that RPM.
- Recheck. The marks should now stay put as revs rise.
Many engines need little or nothing here. Only fill it in if you actually measure drift. It sits in the trigger setup in NSP.
