DAMN.. MY DAM DROPPED

One of the most common questions I see regards Dynamic Advance Multiplier (DAM), and yesterday I noticed another tuner correct the person that was misleading the author of the post. This really pushed me to write this simple post in hopes that it can shed some light on everything DAM related.

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Well, what is DAM? Should I be worried if its less than 1? ( I absolutely hate when people ask people that they don't know if they should WORRY) What does DAM do? Why would the engineers at Subaru create DAM in the first place? To understand what DAM is, we have to know what "knock" is.. and no, feedback knock is NOT rod knock..

"Sometimes knock is also called detonation. Detonation is characterized by the air/fuel mixture spontaneously igniting during the compression stroke. The force of this early, unintended explosion is counter to the direction of the piston and results in a sharp increase in cylinder pressure. The increased pressure can exceed the design limits and potentially cause damage. These events typically result in an audible noise that can sound like a “ping” or “knock.” The ECU picks up on this noise with a microphone hard mounted to the engine block and listens for specific frequencies that indicate a knock event. Any number of conditions or factors can induce detonation. The sources are varied but are generally due to increased cylinder pressure, high temperatures, or reductions in effective octane level.

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Worried? Don’t be! Detonation events are inevitable and will occur from time to time on any modern vehicle running on pump gas. Your car is built to recognize these events and take the appropriate action to defend against them causing any damage. The Subaru knock detection system tends to [highly] err on the side of caution. This makes it common to see “false knock.” False knock occurs when the ECU corrects for a knock event but the noise registered is due to other noises that aren’t necessarily detonation or harmful to the engine. This often happens accelerating from a stop while letting the clutch out, during gear shifts (more so if grunting while shifting), accelerating at low RPM in a high gear, under cruise on the freeway, and during abrupt throttle changes."

Now that we have a pretty good understanding of what knock is, lets look at the relevant monitors/gauges you typically watch and worry over while looking at your accessport.

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"DAM: represents a global adjustment to ignition timing. If this value is anything less than ideal, it’s a quick indicator something [may not be] right (unless immediately following an ECU reset/reflash). On an 02-05 WRX the values will range from 1 to 16, 16 being [the] ideal [number]. On all other Subaru's [32-bit], the value is expressed as a decimal from 0 to 1, the ideal value being 1.

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Feedback Knock Correction: is a real-time timing correction the ECU makes based on a perceived noise. The ECU immediately pulls timing (the amount of the Feedback Knock Correction value) and adds timing back (value rises to 0) assuming no further noise is detected.

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Fine Knock Learning: represents minor learned corrections currently being applied by the ECU as a product of historical noise. These values are reset if the DAM value is changed; once DAM has stabilized, any learned corrections will be intermittently evaluated for sanity when certain thresholds/conditions are met. Fine Knock Learning is learned (and thus applied) for specific ranges defined by load and RPM; once a correction value has been learned into a particular range, it will be applied whenever the engine is operated within that range."

Let's dive into the DIT DAM strategy as this is the most common car that is seen with these "CATASTROPHIC" dam reductions.

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"The newer DIT car’s (direct injection turbo – 2015+ WRX and 2014+ FXT) strategy is a bit more reactive. This is intentional and is expected since “premium” fuel is not required on the DIT vehicles. The strategy has changed and is comparable to what may have been seen as Fine Knock Learning in the earlier non-DIT cars may now result in a drop in DAM in the DIT cars. It shouldn’t be surprising to see a drop in DAM on the DIT vehicles (as it is on early cars where DAM being less than ideal is an indicator there is an issue) especially running lower octane fuels. How long the DAM takes to return to 1 is not indicative of how serious the knock event was and does not mean the car is still knocking. In order to advance the DAM on DIT vehicles, you have to drive in specific load/RPM ranges without knock. Determining whether there is a a potential issue on a DIT vehicle requires considering how low the DAM has dropped and what other knock responses ( Knock Feedback Correction and Fine Knock Learning) look like overall."

Essentially for these DIT cars, DAM is allowed to move, and no it doesn't proportionally equate to power output like I saw commented the other day "if your dam is .8 then you only get .8 of the power." Lets look at an example in Accesstuner (tuning software), the example map is from a Cobb OTS map for a Stage 1 + SF Intake 15 WRX on 93 octane.

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The first picture is the dynamic advanced base correction for the DAM numbers you might see on your accessport. essentially the bottom number in green is the multiplier that will be used for the 3rd picture. Let's take .500 DAM, and the corresponding multiplier of .5 so its easier to calculate. When we look at the 3rd picture, the "Dynamic Advance Base" which is just fancy words for extra timing to adjust for fuel quality, we can see that the highest amount of EXTRA timing it will give is 5.63 during the high load regions. If the DAM is .5 and the multiplier is .5 5.63 x .5 is 2.815 which means your engine is still getting 2.815 EXTRA degrees of timing to the base ignition table. *Disregard the "dynamic advance adder" mentions in the descriptions as they are zero-ed out in cobb maps and almost every protuner tune*

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