What Is DAM (Dynamic Advance Multiplier) on a Subaru Datalog?
DAM is a number the ECU uses to scale how much ignition timing it is willing to run. On a healthy car it sits at 1.0.
What it is
DAM, the Dynamic Advance Multiplier, is a global multiplier on timing advance in Subaru ECUs. It runs from 0 to 1. At 1.0 the ECU allows all of the timing in its tables. If the ECU detects enough knock, it can lower DAM, which reduces timing advance across the whole map until conditions improve.
What 1.0 means, and what lower means
A DAM of 1.0 in a datalog is what you want to see. A value below 1.0 means the ECU has pulled back timing broadly, not just for a moment. It can recover over time, so one log is a snapshot.
APDataview's default rule flags any DAM below about 0.999 for review and treats a value below about 0.75 as serious. Those are APDataview's settings, and a tuner can change them.
How it differs from feedback knock
Feedback knock correction is the live, moment-by-moment pull. DAM is the longer-term, global response. Seeing both together, repeated corrections and a DAM under 1.0, is a stronger signal than either alone.
What to check next
- See where the DAM drop happened in the log and what the engine was doing then (load, boost, temperatures).
- Check fuel quality and the air/fuel ratio under load.
- Ask your tuner whether the map is suited to your fuel, altitude and conditions.
- Log again and see whether it stays at 1.0.
If your log has no DAM channel, the check simply cannot run. That is not the same as DAM being fine.
Check your own log
Upload a COBB Accessport log to APDataview and see whether this shows up in it, with the exact stretch of the log behind every finding. It is free, and the same log always gives the same result.
Check my log free →Common questions
What is a good DAM?
1.0. It means the ECU is not holding timing back.
Does DAM reset on its own?
It can recover during normal driving, and can be reset by a reflash or battery disconnect. So a log shows DAM at that moment, not its history.
Is DAM the same on every car?
No. It is a Subaru ECU concept. Other ECUs use different knock-learning systems.
Related guides
General information only. APDataview reads what the ECU recorded and cannot see your engine, fuel or hardware. It is another tool in your toolbox, not a substitute for professional diagnosis or tuning.