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GT-R: (DBA) Dynamic Advance Explained

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DBA ignition timing is very complicated but elegant.  DBA cars have the authority to add or take away timing as needed.... as the fuel will allow.  This Dynamic Advance (DA) is a critical part of the flexibility of these newer ECUs.

DBA cars are set up to always advance timing in the absence of knock.  The absolute limit of timing advance in the absence of knock is determined by a 3d table with RPM and Load axis and max timing increment as the z data.  In the stock USDM 2012 or 2013 ecu the max positive DA is 1 or 3 depending upon load and RPM.  This means that in the absence of knock the ECU will add up to 3 degrees of timing to the base timing table.  Interestingly, the JDM ecu will allow up to 5 degrees of extra timing which is not surprising considering the generally high quality of Japanese fuels.

The table that determines the maximum timing addition in DBA cars looks like this for USDM stock>

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The stock base timing table for the same DBA GTR looks like this:

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So the next question is how much advance can be removed.  The same dynamic advance strategy is used to reduce timing (reduction from that in the primary advance table).  In this case engine noise considered knock is constantly accumulated and then a corrective reduction in DA is created.  This negative DA is limited to approximately 9 degrees and can vary up and down in response to more or less engine noise.

This is the basic strategy for DBA ignition adjustment.  The most severe knock will produce a "limp" mode.  In limp or high det mode a separate "high det" timing (much lower timing) and richer fuel mixture are used.  The trigger for limp mode is a long term negative dynamic advance above 4 degrees.   A single 4 degree timing removal will not produce limp mode but a long term and severe reduction will.

For the soon to be released DBA maps for COBB Tuning i adjusted the DBA timing to be less aggressive.  That is, i created 4 different octane maps and for all but 100 octane i took away the ability of the stock ECU to ADD timing.  These cars are designed to ping with the stock DBA control and that simply is not acceptable to COBB customers.  I prefer to tune to the conservative limits of the fuel.  Prevention of knock and a steady tune that does not ADD tons of timing is the best way to make these cars more consistent.  The forthcoming COBB DBA calibrations come in 4 different octane flavors to meet the needs of the car without using knock or ping to adjust.  Nissan's stock timing strategy is too aggressive for all but the best quality 93 and 94 octane fuels in the US.  COBB tunes will cover the full array of octane in the US:
California 91, 91, 93, and 100 octane.

Only in the 100 octane map did i leave the ability of the stock ECU to add timing in the absence of ping.

Below is a bit of what i wrote in the GTR tuning Guide for COBB.  It compares and contrasts CBA and DBA timing strategies>

E: Tuning Ignition Timing (CBA 2008 to 2010 world market, 2009-2011 USDM)
Ignition Timing tables - The most important tables for ignition timing are Ignition-Low Det and Ignition HI Det.
These tables are referenced by Theoretical Pulse Width and engine speed. Logging these parameters will allow you
to reference the specific regions of these table that may need to be edited to produce optimized ignition timing.
Dynamic Ignition timing computation - The Nissan GT-R uses a complex computational process to constantly
calculate optimal ignition timing. An internal mathematical model of engine function together with an array of sensor
information is used to calculate ignition timing. The values in the timing tables are referenced within this
computational process but are NOT traditional ignition timing in degrees before top dead center as most tuners will
recognize. These numbers are best thought of in terms of fuel burn time. The numbers in these tables do heavily
impact timing calculations so timing can be adjusted. Higher values will lead to higher ignition timing and lower
values lower ignition timing. For example, a one increment increase in table values will lead to 1 degree increase in
ignition timing.


Detonation based timing adjustment - Ignition timing is also adjusted in response to detonation. The ECU actively
reduces timing in response to detonation. Timing adjustments in response to detonation are logged with the “knock
Sum” monitor. Each knock event results in a -307 knock sum change. 1 degree of ignition timing is removed for
each 256 of knock sum below zero. Only at very high knock levels will the ECU switch to the High Detonation
Ignition map.


Generally speaking, higher ignition timing supports higher torque and greater power. However, ignition timing
should be increased with great caution. Higher timing yields higher cylinder pressures and this is limited by fuel
quality and the mechanical limitations of the engine. Too much timing will produce knock correction when fuel
quality is limiting. When fuel quality is high, ignition timing should ONLY be added when its addition produces a
substantive increase in torque and power. If increased timing does not increase torque the extra cylinder pressure
is simply producing unnecessary stress on engine components.


F: Tuning Ignition Timing (DBA 2011+ world market, 2012+ USDM)
For 2011+ world market (UDSM 2012+) GT-R Nissan began using a new strategy for controlling ignition timing.
This new timing control strategy, designated DBA, represents a completely different approach to ignition control,
Cpyright © 2012 COBB Tuning Products LLC. All Rights Reserved | www.cobbtuning.com 44
Fully Tuned VE table for a 2009 GTR with larger turbochargers. Note higher than default values
and the generally smooth shape of the VE relationship as manifold pressure increases.
compared to earlier CBA GT-R, but one which will be more familiar to engine calibrators. Earlier CBA ignition
control used a complex calculation of burn time to actively determine ignition timing and referenced tables were,
consequently, referencing unfamiliar units. In contrast, DBA strategy look up tables are all referencing ignition
timing in Degrees Before Top Dead Center (DBTDC) and thus use a more commonly understood quantization of
timing control. Despite the familiar language, DBA ignition control strategy is very complex utilizing an elegant
timing adjustment, initiated by knock sensor activity, that can both add and subtract ignition timing. This so called
Dynamic Advance (DA) and its control is key in producing a stable DBA ignition based calibration. In addition to DA
based timing adjustment there are multiplier and threshold based timing adjustments for Coolant and Intake air
temperature.
Degrees before top dead center for all DBA tables: DBA ignition does NOT use a 'burn time” type of calculation
used for CBA. DBA ignition tables are traditional degrees before top dead center. The most important table for
high load DBA timing strategy is “Ignition Low Det (Native - DBA strategy)”. This is the main timing table for DBA
vehicles and is noted in traditional degrees before top dead center.
Final timing = base timing + knock (Dynamic Advance) + temperature compensations
High load DBA ignition timing = Base timing table (low or high det depending upon detonation history) + Dynamic
Advance (timing actively and quickly added or removed based upon current knock levels) + Temperature correction
(Timing added or removed based upon air and coolant temperature corrections).
Low load or cruising timing is calculated more simply than high load (no knock based feedback but some
temperature offsets). However, high and low load timing are always compared and the ECU uses the lower of the
two, which under load is always, high load timing described in detail here.
Dynamic Advance (DA). DBA timing uses a complex strategy to both add and subtract timing in response to engine
detonation levels. To optimize performance the stock ECU, in the absence of knock (low knock levels) can add as
much as 1 to 5 degree of ignition timing. Under conditions where engine knock exceeds the noise threshold in the
“knock sensitivity” tables the ECU can take out as much as 9 degrees of timing. Understanding how to limit these
stock ECU induced timing variations is key to producing a stable DBA based performance engine calibration. The
sequence of events that calculates DA is as follows:
5) Engine noise = (knock sensor)
6) Knock counter (calculation) = Short term knock history (Engine noise*time, based on engine noise and
compared to Knock Sensitivity)
7) Dynamic Advance (DA) = knock counter * knock multiplier (Table)
Knock multiplier = (table based - decrement or increment). Knock counter is multiplied by the table based
decrement (Dynamic Advance – Decrement (DBA)) to remove timing which removes timing in response
to detonation. In the absence of detonation (low engine noise) timing is added according to the base timing
increment multiplier (Dynamic Advance – Increment (DBA)).
8) Final DA is calculated as above and compared to limits as outlined in several tables that define the
minimum and maximum DA under low or high det mode as the table name indicates.
High Detonation Mode – High Det, Limp or Safe mode is entered when the knock counter for DA stores a learned
value of -4 degrees for a long duration. Entering high detonation mode switches active DBA mapping to the high
det tables for ignition and fuel (Ignition High Det. (DBA), Fuel High Det.). Limp mode is maintained until the ECU
is power cycled through a key on off.


Regards
Tim Bailey - COBB Tuning.

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