2008-2009 Porsche 911 (997.1) GT3
2008-2009 Porsche 911 (997.1) GT3 RS

Tuning Guide and Table Definitions

This tuning guide is broken into the basic components of tuning a Porsche 997.1 GT3/GT3 RS and the tables associated with each of these components. The guide outlines basic tuning strategies and defines tables for each major tuning category, such as fueling and ignition timing.

Step 1 – What is the mechanical configuration of the vehicle?

The first step in tuning a Porsche 997.1 GT3/GT3 RS is choosing a COBB Tuning Off-The-Shelf (OTS) calibration that most closely matches the mechanical components and modifications of the vehicle to be tuned
The Stage1 calibrations are designed for vehicles with no aftermarket parts at all. These are a good starting point even for vehicles with basic modifications.

Step 2 – What fuel is the vehicle using?

Note that COBB Tuning offers calibrations for four different fuels: 93 octane (98 RON), 91 octane (95 RON), ACN91 (91 octane from Arizona, California, or Nevada) and 100 octane. Higher octane ratings indicate higher quality fuel that burns more slowly and can support higher cylinder pressure. This difference in fuel will determine how the car is tuned. Higher octane fuel supports more ignition timing, and leaner air-to-fuel mixtures compared to lower octane. Using a map designed for high octane with low octane fuels can result in damage to the motor.

Step 3 – What type of air intake is on the vehicle?

The 997.1 GT3/GT3 RS utilizes a mass air flow (MAF) sensor located downstream to the air filter to measure the amount (mass) of air entering the motor. This air flow measurement is CRITICAL for ignition timing, and fuel. This sensor reports the amount of air entering the motor, which is used to determine load. Many tables inside the ECU use Load and RPM as their axes. Therefore, it is important that the car is free of leaks of any kind before or after the MAF to be sure of proper running condition.

Step 4 – Calibration refinement on a chassis dynamometer.

A: Connect the Accesstuner software to the Accessport equipped 997.1 GT3/GT3 RS

Open the selected starting calibration in the Accesstuner software then configure the Accesstuner software to connect to your vehicle. Attach the OBDII connector to the vehicle and, to your Accessport (if applicable), then connect the associated USB cable to your computer. Press "Ctrl+F" to configure the program. Select the directory in which to store your data logs under the "Logging" tab.

B: Log critical engine parameters while testing.

Accesstuner software allows the user to sample and record critical engine parameters including sensor information and commanded engine function. Open Accesstuner and load the calibration currently flashed to the vehicle. Attach the OBDII cable to the vehicle and the computer. Press "Ctrl+F" to configure the logged parameters in the "Log List" tab, and those displayed in the Accesstuner "Dashboard" through the "Gauge List" tab. The Dashboard, a screen that reports active engine and sensor parameters, can be accessed by pressing "Ctrl+B." It is critical to actively monitor the condition of the motor during tuning and this screen is the single best way to do so. These data monitors allow the tuner to determine if a calibration is performing correctly. Accurate and deliberate assessment of logged parameters is the only way to avoid conditions that may damage the motor.

If more than 12 parameters are selected at any one time, the logging can slow down. The Porsche can log 20 parameters around 20 Hz, so while still pretty fast the less non-essential parameters the better.

C: Tuning for appropriate Air to Fuel Ratios (Lambda)

The ideal air to fuel ratio (AFR) depends upon fuel quality, engine design, fueling model (port injection, DISI, diesel, etc.), heat exchanging abilities, and other variables. Higher octane fuels are more stable at higher cylinder pressures, and are more resistant to preignition. Leaner AFRs can produce higher power, but also create more heat that may lead to unsafe preignition. Lower octane fuels, such as 91OCT (95 RON) and ACN91 (Arizona, California and Nevada 91 octane), are less resistant to detonation and require a richer (fewer parts air per parts fuel) AFR for safer operation. Richer AFRs produces less heat, protect against detonation due to a cooling effect of the excess fuel and usually produce less power. We have found that the 997.1 GT3/ GT3RS actually tends to make more power by adding a little bit of fuel at the top end of the power curve. Target air fuel ratios of around .84(ʎ).

Air to fuel ratios for these vehicles are directly impacted by several tables. The Porsche fuel control system operates a closed loop control strategy. This means that the car runs a set of wideband air fuel sensors, and is constantly adjusting the fuel targets based on a collection of variables. The fuel target under wide open throttle is dictated by the Target Fuel Driver Demand Map. Setting a target in this table will yield the desired Air Fuel desired, as long as some of the others conditions are correct.

Since the car uses a closed loop system to control fuel, the ECU is constantly monitoring and adjusting short term and long term fuel trims. You can make changes to the short term corrections by adjusting the Fuel Correction Maps. These maps are dependent on valve timing to determine which map is being used at which time. They are a basic multiplier setup so 1.00= 0 in terms of percentage of a correction. Anything above 1.00 IE. 1.10 is adding fuel, so in this case it would be an additional 10% fuel, .9 would be a -10% correction.

A fuel mixture that is too lean will contribute to uncontrolled combustion, excessive heat, detonation and possible engine damage. The objective is to run the car at the richest air to fuel mixture possible that does not sacrifice power. Ultimately, the best air to fuel can only be determined in concert with changes to ignition timing. For example, in some cases a comparatively rich air to fuel mixture can be run with more ignition timing than a leaner mixture. This combination may produce higher power than a lean mixture with less ignition timing. Generally speaking, the air to fuel and ignition timing combination that produces the best power while minimizing heat is the desired calibration. Of course, this ideal is not limited to ignition timing and fuel, but is also a balance of variable cam timing and other factors.

D: Tuning Ignition Timing

The ignition control strategy in the Porsche 997.1 GT3/GT3 RS is very dynamic and has a lot of contributing variables to determine the overall ignition timing value. Since the car is always trying to calculate an overall best efficiency, it does this for ignition timing by using the optimal ignition timing maps and using a target lambda (ʎ) =1 as a base for the efficiency. Additive corrections get made and it forms a variable in the ECU that is "optimal timing." This is the basis for all the ignition calculations in the car. The Porsche uses a strategy of two states of cam timing as well. These points will dictate which of the ignition timing maps are used and when. The actual ignition timing uses some additional variables and then comes to the conclusion of ignition timing based on the difference between the optimal ignition maps and the base ignition timing maps. We recommend not changing the optimal ignition timing maps and changing the base tables instead, as these are more realistic ignition timing values, and will blend with the optimal ignition timing maps. Base Ignition Timing Map 4 has been found to be the high lift, high load timing map used by the ECU so we suggest making changes to this table to control ignition timing under load.

E: Knock Control System

The knock control strategy on the Porsche 997.1 GT3/GT3 RS is very complicated and uses individual cylinder knock control to make changes to the ignition timing at all times. The system is very sensitive and thus almost always has some sort of feedback. You can monitor knock retard and ignition correction in each cylinder. This is the best way to check for detonation, and to ensure a safe running vehicle. The closer to 0 the better, since it is dynamic it will also add timing, but if it always into the negatives (-1 degrees and below) this is the car registering detonation. Since the car is very dynamic it is made to be sensitive. If you are getting values past -6 degrees, lower ignition timing, or add more fuel and see if you can bring the values back towards 0. Running a race fuel will also help in getting the knock control values closer to zero.

If running built engines you can change the knock detection thresholds in the software. By raising these tables you are de-sensitizing the knock control system. THIS SHOULD BE DONE WITH GREAT CARE AS DOING THIS CAN RESULT IN ENGINE DAMAGE AS KNOCK CONTROL BECOMES LESS ACTIVE!!

Generally speaking, higher ignition timing supports higher torque and greater power. However, ignition timing should be increased with great caution. Higher timing yields are limited by fuel quality and the mechanical limitations of the motor due to higher cylinder pressure. Too much timing will produce knock sums when fuel quality is the limiting factor. 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: Porsche Torque Control Strategy

The Porsche Bosch ME7.8.2 ECU uses torque control to influence how the car behaves on power and off power. This system uses input from a wide variety of internal and external sensors to dictate how the car reacts in certain conditions. Data logging load will be useful in determining if you are surpassing a target.

This ECU uses various methods to control torque output, such as closing the throttle plate when the car overshoots a target torque table. So you will always want to monitor throttle plate opening as it is a way for the car to lower the torque output. Other methods include lowering ignition timing, or changing air fuel ratios. So you want to be sure that the car is optimally calibrated in all conditions.

G: Tuning Variable Cam Timing (Vario-Cam Plus)

Porsche uses a variable cam timing system that changes cam duration at different engine speeds, but with Vario-Cam it also changes the valve lift dependent on cam phasing. This provides very good efficiency in all driving ranges as it can change lift using hydraulic tappets with a type of attachment pin. There are 3 lobes on the cam and the center is the "slow lift" the outer 2 lobes are the fast lift and pertain more to making more power and a higher lift. This helps to make more power through the power band. The cam timing can be changed in the software. In order to be see results from this type of tuning a chassis or engine dynamometer is required.

H: Integrating all tuning parameters for the ideal calibration

The ideal calibration for your Porsche 997.1 GT3/GT3 RS is a combination of all major tuning areas outlined above. Generally speaking, the Porsche 997.1 GT3/GT3 RS will make the most power when it runs a lean AFR with the maximum amount of ignition timing allowed by the ECU without detonating. However, the theoretical ideal of 12.5:1 air to fuel ratio and high ignition timing may not be realistic for all configurations and fuels. Calibrations should be thoroughly tested on a chassis dynamometer, where the impact of tuning is easily measured, to determine if they are ideal for the vehicle, its mechanical components, and its fuel. For example, addition of ignition timing that does not result in increased torque is not ideal because it produces additional stress on engine components without a perceivable benefit. Same is true of fuel tuning. If the vehicle can operate at a richer air to fuel ratio without losing power, it is ideal to do so.

I: Precautions:

Fuel – The stock fuel injectors are ~550cc. These vehicles have well designed fuel systems, but if run on ethanol fuel they will run out of injector on the stock injectors and fuel system. Stock fuel pressure is 3.8 bar in the Porsche so make adjustments accordingly.

Ignition Timing- Please make sure to log knock in each cylinder to be sure that the car is not detonating as this will cause damage to the motor.

Folder: Brake Boosting

Delay Time for Limit when the Brake Pedal is Pressed

Table Description- Amount of delay to closing the throttles when the brake pedal is pressed down.

Tuning Tips- Increase this value to ensure that the throttle does not close when trying to use left foot braking. We suggest still leaving a limit on this as to ensure that the car cannot be run for too long in this mode and to ensure that there is a still a safety device in place in the event the throttle is stuck in the open position.

Precautions and Warnings – Modify this at your own risk!! This is a safety device and should only be modified with the knowledge of how to turn a car off in the event of a throttle malfunction!!

Maximum Throttle Angle with Brake Pedal Pressed

Table Description- Maximum throttle percentage allowed while the brake pedal is pressed.

Tuning Tips- Increase this value to ensure that the throttle does not close when trying to use brake boosting. We suggest still leaving a limit on this as to ensure that left foot braking cannot be run for too long.

Precautions and Warnings – Modify this at your own risk!! This is a safety device and should only be modified with the knowledge of how to turn a car off in the event of a throttle malfunction!!

Minimum Engine Speed for Pedal Limit when the Brake Pedal is Pressed

Table Description- Maximum throttle percentage allowed while the brake pedal is pressed.

Tuning Tips- Increase this value to ensure that the throttle does not close when trying to use brake boosting. We suggest still leaving a limit on this as to ensure that left foot braking cannot be run for too long of a time.

Precautions and Warnings – Modify this at your own risk!! This is a safety device and should only be modified with the knowledge of how to turn a car off in the event of a throttle malfunction!!

Minimum Vehicle Speed for Pedal Limit when the Brake Pedal is Pressed

Table Description- Minimum speed the vehicle needs to be traveling in order to activate the throttle closure feature.

Tuning Tips- Increase this value to ensure that the throttle does not close when trying to use brake boosting. We suggest still leaving a limit on this as to ensure that brake boosting cannot be run at too high of a vehicle speed.

Precautions and Warnings – Modify this at your own risk!! This is a safety device and should only be modified with the knowledge of how to turn a car off in the event of a throttle malfunction!!

Folder: Cam Timing

Intake Cam Timing Angle & Intake Cam Timing Angle High Valve Lift

Table Description- Degrees BTDC (before top dead center) that the intake cam opening. High Valve Lift map is typically utilized when trying to achieve maximum performance at wide open throttle.

Tuning Tips- Modify these tables to try and achieve optimum cylinder filling and to help increase volumetric efficiency.e

Folder: Fuel

End of Injection Angle

Table Description – This table helps to adjust the end of injection timing for the fuel injectors. The z data values are in degrees BTDC. The idea of this table is to inject fuel with the intake valve open for best efficiency. This is changed to try and increase atomization but sometimes this can be hard. It is also sometimes best to inject fuel onto the closed inlet valve if you feel like the injectors you are using are not atomizing fuel well. This can help atomize the fuel in the intake port but fueling accuracy does decrease. This can also be helpful in starting cars as well. These tables are also useful if you have a car with larger injectors and they are producing black smoke under wide open throttle.

Fuel Correction Map 1 & 2 and Variant 1 & 2

Table Description – These are the tables that help to correct volumetric efficiency inconsistencies. If you need to get more fuel due to the fuel trims being off, then you want to make fuel changes in one of the four fuel correction maps. These maps are defined by injector open time and cam timing lift.

Tuning Tips – These tables can be used as a "VE" table when running the car MAFLESS. There are multiplier tables so changes to them should be close to linear in terms of percentage applied in the trims and the amount added in the tables.

Injector Latency

Table Description – This table contains latency values used to tell the ECU how much latency is needed to properly control the fuel injectors; the breakpoints are in battery voltage. All fuel injectors require a certain amount of "dead" time to fully open which is referred to as Injector Latency. The amount of latency an injector requires is dependent on several factors, such as the size of fuel injectors, viscosity of fuel, manifold pressure, and fuel pressure. Lower battery voltage requires increased injector latency (dead time). Likewise, higher fuel pressure may also increase injector latency. The data in this table is represented in milliseconds. A higher value will open the fuel injector sooner, thus the total IPW will be greater; a lower value will open the fuel injector later, thus the total IPW will be less.

Tuning Tips – Most fuel injector manufacturers will be able to provide you with injector latencies by voltage. The drivers used to develop these latencies may be different than the injector drivers in the stock ECU, so further modification from the published values may be necessary and you should not be concerned if your final values differ from manufacturer documentation.

One way to find the correct latency (or at least the latency that works best with the injector drivers in the ECU and your particular injectors) is to begin with stock fuel pressure and the stock intake system, then set the proper scale value for the injectors you are using based of the scalar calculation. Once you have established a proper injector scalar value, start the engine and let the car warm up (coolant temperature between 170-200˚ F and intake air temperature +/- 15 degrees F of ambient temperature) then re-set the ECU so your fuel trims start at zero. Start the vehicle again and watch the SUM of your fuel trims, STFT + LTFT. If you see that the SUM of your fuel trims (STFT + LTFT) is positive, add injector latency until you see the SUM of your fuel trims come closer to zero. You will have to test this throughout the operating range of the engine. Try to avoid sudden throttle movements during this process to avoid corrections based on the Tip-in Enrichment tables. If you see that the SUM of your fuel trims is negative, reduce injector latency until you see the SUM of your fuel trims come closer to zero. Again, you will have to test this throughout the operating range of the engine - the entire MAF curve. Try to avoid sudden throttle movements during this process to avoid corrections based on the Tip-in Enrichment tables.

This is part of a calibration process that will bring you closer to the ideal settings necessary to properly control your fuel injectors. Please take into account that you will most likely have to calibrate the fuel correction maps to get the trims where you want them at different operating conditions.

Injector Scaling

Table Description – This table contains a singular value used to represent the fuel injector size or flow rate. Any changes to this value will affect ALL tables within the ECU related to fuel delivery and load calculations. When using stock injectors with gasoline, this value DOES NOT need to be altered. When adjusting this value, a lower number represents a LARGER injector, whereas a larger scale value will represent a SMALLER injector. This value in the Porsche is a factor of total opening time. A larger injector will need less time open to supply the same amount fuel, hence the smaller number for a larger injector.

Tuning Tips – In order to calculate the injector open time Porsche uses a large equation to come to the final value. In this equation they calculate air density as well as a slew of other variables. One of these variables is calculating an injector constant with n-heptane. Since some injector companies don't use this as a calibration medium anymore, this can sway the final result of the injector scaling since the density of the two fluids is different. So depending on injector manufacturer you may need to adjust the scaling either up or down to come to a value that is close according to the fuel trims.

With that being said here is the best way to come up with the proper value range for larger injectors:
Y= 44.0901/X so in order to get a new injector constant value divide 44.0901 by your injector size.
Example- Injector Constant= 44.0901/1000(cc)
Injector Constant= .04409 or about .045.

MAF Correction

Table Description – This table is used to correct for fluctuations in the MAF signal due to turbulent airflow. This can prove to be useful for cars that are using different intakes that have different size or geometry in relation to piping.

Minimum Injector Pulsewidth

Table Description – This table is the lowest injector pulse width the ECU will allow the injector to operate at.

Tuning Tips – If running an injector is very large like a 2000cc injector, then you may need to increase this value to make sure that the deviation of the injector at low pulse widths is within range. For example if using an Injector Dynamics 2000cc Injector then you would want to raise this value to around 1.0ms or something similar to make sure that the deviation is within a reasonable percentage.

Target Fuel Driver Demand Map

Table Description – This is the lambda target at wide open throttle that you are commanding from the car. The ECU will do its best to try and reach this target by using short term and long term fuel trims as well as data from other sensors.

Tuning Tips – You want to ensure that the lambda target is safe under wide open throttle and not too lean as this can cause damage while at the same time ensuring that it is not too rich as it will hinder performance. We recommend a value of around .78-.81 under full load.

Target Fuel Map for Component Protection; Target Fuel Map for Component Protection 2

Table Description – These two tables are used as protection maps incase temperature limits are reached. They are used as a precaution to cool down the cylinder by adding more fuel than what is requested in the Target Lambda Driver Demand Map. There are two of these maps, one for each bank. They will get used when modeled temperatures get too high in some of the sub systems (EX-EGT)

Tuning Tips – Set these to where you would want a safe air fuel mixture. Avoid setting these too rich as overly rich conditions and retarded ignition timing can cause high EGT's. Also try to set them the same so that you do not have varying conditions from one bank to another.

Folder: Idle Control

Target Idle Table

Table Description – Target idle requested for the car based on gear and coolant temperature. Set this higher if the car has cam shafts, or generally just need the idle to be higher.

Folder: Ignition Timing

Base Ignition Timing 1,2,3,4

Table Description – These are the base ignition timing tables. These are the lower end of the timing maps that are used. Most of the time the timing is close to these values if the knock control system is active. These tables get selected based on cam timing.

Tuning Tips – Make changes to Base Ignition Timing Map 4 for high load, high lift tuning.

Minimum Ignition Timing

Table Description – This dictates the minimum ignition timing value

Optimum Ignition Timing 1,2,3,4

Table Description – These are the most ideal timing values for the car, and are used in the whole ignition efficiency calculation. These are based on temperature and cam timing reference to select which map is used.

Tuning Tips – Typically you do not need to change these tables. If you need to make changes to the ignition timing, you want to make them to the Ignition Timing Base Tables.

Folder: Knock Control

Knock Control Threshold Cylinder 1-6

Table Description – These thresholds are made to determine when the knock control system becomes active. Raising these thresholds will make the car less likely to pull timing when it hears something it deems as a knock event. Use this on built motors when the harmonics of the engine can change the amount of noise the knock sensor deems as knock, when in fact, it is just engine noise. The numbers are for each individual cylinder.

Timing Reduction per Knock Event

Table Description – The amount of timing retard in degrees that gets pulled during each knock event.

Tuning Tips – Change this if you feel that the car is pulling too much timing or too little timing depending on the knock event. USE THIS WITH GREAT CAUTION!

Timing Refresh Rate Post Knock Event

Table Description – This is a raw value for how fast timing comes back in after a knock event.