Nissan GT-R Speed Density

Speed Density Tuning Guide

This second of the tuning guide is to be used for speed density based tuning.  Much of the logic and tables are the same for MAF or speed density so much of this second section of the tuning guide is a duplicate.  However, there are critically different fuel and load calculation differences across these two tuning types and this section focuses on SD tuning strategies.

How to create SD based calibrations

GT-R Accesstuner software for SD integrates custom logic and new tables to allow SD based tuning. Once you have selected the appropriate year and world region of the car the proper base parameters are automatically loaded to allow SD tuning.  There are a few key parameter that need to be set up in order to create a base Speed density tuning calibrations.   

• Set the fuel multiplier to STOCK. This value is often increased as part of tuning larger diameter intakes with MAF based tuning.  This value must be STOCK for SD calibrations.
• Set MAF calibration A to stock values
• Set MAF calibration B to stock A values (A=B at all MAF voltages)
• Set the injector scalar to match the flow of the installed injectors (570 for stock)
• Certain codes will need to be turned off in order to run Speed Density Tune (CTO!)
  • P0101
  • P0102
  • P0103
  • P010b
  • P0236
  • P0238
  • P0240
  • P0328
  • P0700

Air Temperature Sensors Reolcated?

Speed density based airflow calculations and fueling commands require an accurate measure of air temperature.  The best place to measure air temperature is after the intercooler and just before the manifold.  It is the temperature of the air entering the motor that is most important.  The standard SD air temperature correction table is set up to produce fueling offsets consistent with this sensor placement.  It is highly advised to move the stock MAF and air temperature sensors to a location just before the throttle body.  Configured in a boost tube after the intercoolers the MAF sensors along with their associated Air Temperature Sensor are in a “blow through” configuration.

Tuning for appropriate Air to Fuel ratios using Speed Density  

The ideal air to fuel ratio depends upon fuel quality. Higher octane fuels are more detonation resistant and therefore can be run at leaner air to fuel ratios. Leaner Air to Fuel ratios produce higher power but also create more heat. Excessive heat can lead to detonation. Lower octane fuels such as 91 octane or 95 RON are more prone to detonation and therefor require a richer air to fuel ratio. Rich air to fuel ratio combustion produces less heat and therefore less detonation. We have found that the GT-R engine can run mid to high 11 Air to Fuel Ratios (AFR) when running quality fuels. Lower quality fuels require mid to low 11 air to fuel ratios.

SD based tunes DO NOT directly measure Air Flow through the MAF sensor.  Instead Air Flow is calculated based upon the ideal gas law.  Air flow  estimated based upon the manifold air pressure and air temperature. These two measures combined with an underlying estimate of engine volumetric efficiency (VE) allow the GTR to be calibrate using manifold absolute pressure as the primary load reference.

SD based tuning utilizes a slightly larger collection of tables to tune for proper AF.   Some of these tables are common to MAF based tuning strategies.  Tables and values that impact fueling for SD based tuning are:1) injector scalar 2) injector latency multiplier and offset 3) Fuel multiplier (leave this STOCK) 4) MAF curve A and B ) 5Primary fuel and ) 6volumetirc efficiency

• Fuel - Injector scalar: For SD based tuning set injector scalar to its flow is cc (for example, stock injectors are 570cc). *Exceptions to this include but are not limited to the use of heavily ethanol based fuels.  In this case Injector scalar is 30 to 35% smaller than standard flow for pump fuels (e.g. 1000cc injectors are scaled to ~1000 for pump fuels but ~700 for E85 fuels)
• Fuel - Injector latency (offset and multiplier – values sames as those use for MAF tuning 3) Fuel Multiplier – Leave this STOCK!
• MAF Curve A and B = set both A and B to stock A values. The MAF curve is used in our custom coding for VE and also used to calculate theoretical pulse width (load for all but the VE table)
• Fuel-Low Det – referenced by TPW and Engine speed. This map designates desired AF ratio. These values are part of the SD fueling model.  Adjusting these values actively changes the calculated injector open time to generate desired AF based upon the internal SD model along with VE table.  Just as with

MAF based tuning the GTR references AF ration at all times and adjusts fueling with Sort and long term fuel trims.   

• Fuel -Volumetric Efficiency (VE). This table offers a means to adjust VE to best match the flow characteristics of a motor.  Any component that changes airflow through the motor (e.g.,exhaust, intake, camshaft, turbocharger) will change VE.  The default VE map is a good starting point for a stock car with stock turbocharger and no to mild exhaust upgrades.   
• Speed Density – Air Temp Based Fuel Correction Air tensity changes with temperature in a predicable manner. Higher air temperature indicates lower density and lower temperature more dense. Fuel calculations must change given this relationship. This table determines this relationship and is ideal for most cars with air temperature sensors located after the intercooler and just before the manifold.  This table is tunable to allow for differences across cars.

Step 1:

Set up the calibration for SD.  Open a default SD calibration in the software and set up for the configuration of the car.  Set up injectors, FM, MAF, and Primary Fuel table to best match the configuration of the car as well as the fuel type.   The default VE table is a good starting point for mildly modified cars.

Step 2:

Run the car under low load conditions and adjust the primary fuel and VE map to create the smallest possible short and long term fuel trims.  As in MAF based tuning, The R-35 GT-R uses two internal wide-band oxygen sensors to monitor fuel mixtures on left and right engine banks. The ECU will constantly adjust fuel to reach this air to fuel target. As a result, the values in Fuel-Low Det are a closed loop target that the ECU will always work to achieve. The active adjustments made by the ECU are monitored at STFT (ALPHA) B1 and STFT (ALPHA) B2. These short-term fuel trims will gradually enter a long-term learned state that can also be monitored - LTFT (KBLRC) B1 and LTFT (KBLRC) B2.

Step 3: Run the car at increasing higher manifold pressures until  the VE map is tuned over the full range of pressures at which the motor will be operated.

Step 4: Adjust the Speed Density – Air Temperature Correction:  The default Air Temperature fuel correction works well when the air temperature sensors are placed in the boost tubes just before the manifold.  Air Temperature based fuel correction can be adjusted for specific vehicle/air temperature sensor location.  Below is an example of a fully tuned Volumetric Efficiency table for a GTR with larger turbochargers.  Note the VE compensations are slightly higher for this car than those indicated in the default table for use with more stock like components

Below is an example of a fully tuned Volumetric Efficiency table for a GTR with larger turbochargers.  Note the VE compensations are slightly higher for this car than those indicated in the default table for use with more stock like components

Fully Tuned VE table for 2009 GTR with larger turbochargers.  Note higher than default values and the generally smooth shape of the VE relationship as manifold pressure increases.