Table of Contents

The factory calibration of the 992 GT3 is fairly robust and allows for both aggressive track driving as well as comfortable, economic street driving.  This car utilizes the Bosch MG1 ECU found in other 992 chassis Porsche 911’s as well as the 4.0L 718, Macan, Cayenne, and Audi models.  Overall calibration strategy is very similar to the 4.0L 718 models.  The naturally-aspirated 4.0L flat-6 found in the 992 GT3 is capable of a higher output than the 718 thanks to significant changes to the components surrounding the motor although the 718 GT4 RS and Spyder RS come close.

Before the Dyno

Getting on the Dyno

Due to the aero elements on the car, attaching sufficiently strong straps for safe dyno operation can be difficult.  For the front, we attached the factory tow hook in the front bumper and secured ratchet straps.  For the rear, the diffuser was removed from the car via 5 bolts and tie downs were bolted onto the rear subframe.  This allows use of chains in the rear but you should ensure that they are not contacting the exhaust.

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We tucked a set of the Rennline tie downs under these two bolts.

Cooling

Much like other mid/rear engine Porsches, sufficient cooling can prove difficult in a dyno cell.  Heat soak is a constant issue that should be monitored.  Extra cooling can be beneficial and use of a portable hand-held fan can help clear hot air from the engine bay.

Traction Control

When driving on an linked-roller AWD dyno, traction control should be turned off.  Errors may appear but can be cleared by some short driving on the street after the car has been removed from the dyno.  When driving on an unlinked or 2WD dyno, Dyno Mode should be used.  In the Accessport Troubleshooting menu, there is an option to enable Dyno Mode.  This will put the car into an operating state where it will allow for different wheel speeds.

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The ECU as a System

Porsche calibrations, regardless of ECU variants, will require torque limits and targets to be adjusted (typically raised).  At the end of the day, being able to adjust those tables and have everything work in concert is your goal.  Within the range of Porsche vehicles there are a variety of tuning strategies which make achieving this goal a different process.  This tends to mean that if you are an expert with 992 911 cars, everything will look somewhat familiar, but you'll still face a small learning curve in terms of exactly which tables require changing.

These ECUs have very well modeled tables looking for a fairly consistent level of vehicle operation.  This means that in order to produce a finished calibration, you'll need to make a large range of changes.  It's not possible to only change one parameter at a time and expect to make sustainable power.  As an example, if you are working to optimize factory ignition timing or fuel, you will not see an increase of power in the presence of the factory torque limits and targets.  In order to make power and tune the car, the best way to start is to push the limits out of the way (but to a safe limit) in order to keep the vehicle's behavior and targets consistent with the power you're targeting for your powertrain and fuel.

In order to preserve the balance of driveability and speed that the factory clearly worked so hard to achieve, it's recommended to minimize the table changes you do make.  This seems counterintuitive when we just told you that you need to adjust more tables than you think, but if there is a change you feel may not be important or related to the desired behavior of the vehicle we recommend returning it to stock.  This makes sure that the character of the vehicle can be preserved, and any undesirable effects from the complex interrelation between tables doesn't cause any issues.

During calibration, you may find that some tables contain only 0’s as an output (z-data) from the factory. Other operating systems or ROMs may contain actual data in these tables. This is an indication that the table is not used or referenced in the particular ROM you are working. We recommend leaving these tables empty. Adding data to them, at best, will typically produce no changes in operation. However, at worst, this may result in undesirable changes. 

Torque Control

Torque Request

There are several tables within the Torque Control>Torque Targets folder that control and describe the relationship between the accelerator pedal position and the torque the engine gives in response.  Because the accelerator pedal acts as a torque selector for the driver and is one of the few ways the driver communicates with the engine, it can have a huge impact on the driveability/character of the vehicle.  Do you want a car that with the slightest input takes off?  Or do you want a mild mannered daily driver.

These tables all function primarily as a torque request, however they can also act as a limiter unless they are set high enough to hit the torque the vehicle is producing.  The GT3 is unique among other MG1 cars in the fact that the values shown in the torque target tables do not relate to the actual torque output measured at the wheels.  These values seem to represent a three dimensional logarithmic function of torque to very high values (over 5000 ft. lbs.).  Since the engine is naturally aspirated and has a very linear power band, torque is directly proportional to engine speed and there is no turbocharger to allow for the ECU to simply “select” the power it would like to make.

In our calibrations we raised the higher demand sections (higher Rpm/Accelerator pedal %) to a higher torque request in order to hit the increased power we were targeting by priming the ECU to want to attain higher power.  In order to maintain driveability we left the lower sections stock.

In areas of RPM / pedal position the vehicle will find itself sitting in or transitioning through frequently (cruise/around town part throttle driving) it's a good idea to make sure there are no abrupt transitions, as that can lead to the feeling of surging or disproportional acceleration while trying to maintain a consistent speed.

Torque Limits

The factory ECU is constantly calculating torque output in order to deliver exactly the output that Porsche designated by using a variety of torque limits.  The purpose behind that is in order to create a calibration that performs the same in all conditions.  This means regardless of temperature, ambient pressure, or other variables it would go after the same amount of power.  Our goal is to remove or adjust these limits in order to produce our new higher power output but still be able to maintain consistency. 

Within the Torque Control>Torque Limits folder, you will find a variety of tables that function as limits.  Other tables contain values that are maxed out, functionally disabling the table. For these cars, we recommend increasing the functional tables by a modest 10-20% as needed. 

A second option in order to remove the torque limits is to disable some of the torque checking procedures (move them out of the way). The tables for the limits can be found in the general Torque Control folder labeled in groups as the Engine Speed Threshold for Valid Actual Engine Torque and Min/Max Torque Comparison Delay.  Functionally these tables set the timer for how frequently the ECU looks at the torque output.  In effect, by increasing the timer delays and adjusting the RPM activation points you can choose when (if at all) the computer is actually referencing the torque limits in some cases entirely removing them from being processed as part of the torque control strategy.

Load Control

For the 992 GT3, load adjustment was not needed for OTS map development using readily available 91/93 octane fuel.  However, there is potential for this to be an effective method of calibration for more power, especially when the engine efficiency is increased through upgraded components or higher octane fuel.

Within the Load Tables folder there are several tables that describe the relationship between relative load and load/airflow/cylinder filling.  These tables function as targets and limits.  Relative load is translated to the cylinder fill target.  The cylinder fill target then creates the airflow request which is translated into torque.  If your cylinder filling and torque limits are all set accordingly, adjusting these tables will allow you to make additional load and power.

This will all be limited by other table limits such as:

• Maximum Load

• Maximum Torque

• Temperature

• Ambient Pressure

• EGT

Relative Load And Cylinder Filling

One thing that can get confusing is that two phrases are used interchangeably in the operation of the ECU (from the factory) Relative Load % and Cylinder Filling and Torque Percentage and Relative Load.

Cylinder filling (both as a target and a limiter) is defined by the relative volumetric efficency of the combustion chamber and the engine’s ability to flow more air into it.  This table is defined as a function of RPM and makes it very easy to see the relationship of cylinder filling to torque as the values look identical when compared to the torque curve of the vehicle on a dyno graph. 

The relationship of load and cylinder fill is fairly similar to the relationship between torque and airflow on the other Porsche platforms as well as VW and Audi vehicles.  In this case the target relative load references the Target Cylinder Filling table in order to determine a target filling.

The other way that Porsche described the relationship between relative load % and cylinder filling/airflow is in the Map Optimum Engine Moment and Optimum Relative Load for Function Monitoring tables.  There may be one or more of these tables depending on the ROM.  These tables are the same data as the Target Cylinder Filling table above but the z-data (Load/Airflow) is now the x/y-axis and relative load is now the z-data.  Just like with the Torque and airflow tables on other vehicles, if you change one of these tables you will need to change them all in order to ensure proper function.

Why change the relationship between cylinder fill and relative load?  In some cases it might be desirable to increase the cylinder fill for the given load.  This will increase power, however any deviation from factory load calculations will impact the way the vehicle drives both in engine response and transmission shifting. To avoid driveability issues any changes made should be limited to the higher load regions and done in an iterative manner with small changes being tested successively. 

Here you can see a modified Target Cylinder Filling table and the associated Map Optimum Engine Moment table which has been modified to match. Both only incorporate changes in high load regions and have been calculated to match.

Ignition

Like many things on this ECU, Ignition timing has a model that it refers to in order to base it’s calculations on “Ideal” conditions under which the car makes the most power possible (which in the real world would require a very knock resistant fuel). The Optimum Ignition Timing tables establish the model for engine behavior and "perfect" timing under ideal (impossible) conditions.  These are not values you should use in the normal timing maps, nor should this table be altered for any stock motor operation, they give the computer an idea of how hard the engine is working/how much power it will make vs the ideal.

The ignition timing on these vehicles is similar to many other VAG products in that the stock ignition timing system works very well in response to meeting the needs of both stock operation and the increased load targets you'll typically see with tuning.  Due to presence of knock on the factory tune, (particularly on 91 octane) timing was reduced in some areas to create a calibration more suitable for that fuel while still having a performance improvement.  On the opposite end of the spectrum, we found that by adding some timing when the fuel allowed it we were able to pick up some power, particularly on 100 octane fuels.

The main ignition tables you'll need to modify are:

• Ignition Timing (Normal) 1

• Ignition Timing (Normal) 2

• Timing Map

• Timing Map Variant 2

These establish the timing under most normal driving conditions based on load and RPM.  While the values in these tables aren't fully identical it's best practice to offset the tables by the same amount when making changes.  I.E. Remove/Add 1.5 degrees from the same point of the table.

You can also use the following tables for use during aggressive driving:

• Ignition Angle for Homogeneous Split - High Valve Lift Exhaust Cam Pos1

• Ignition Angle for Homogeneous Split - High Valve Lift Exhaust Cam Pos2

• Ignition Angle for Homogeneous Split Operating Mode - High Valve Lift

• Ignition Angle for Homogeneous Split Operating Mode - High Valve Lift 2-Var.

Delta Timing from Continuous Knocking

The newer operating systems used in MG1 Porsche applications have a new monitoring system labeled as Delta Timing from Continuous Knocking (DTCK). This system in the software acts similar to the DAM system in Subaru, as it is actively adjusting the allowed ignition timing based on a learned knock response (knock observed over time).  The system shouldn't impact the ability to tune the vehicle provided the ignition timing values you target don't cause heavy knock.

The monitor for DTCK is actually reporting the potential timing reduction that can be applied in the event that continuous knocking is recorded.  It is NOT a measure of timing actively being removed.  If you refer to the final ignition timing of any given cylinder in a datalog, you’ll see that it does not incorporate the output value from DTCK.

Fuel System

These vehicles do not have a fuel table for full load.  The only fuel control available is related to EGT control and component protection.  So, for the most part, under all conditions the car will target a lambda of 1 (14.7:1 AFR).  The only times there are changes to the AFR is when the vehicle goes into component protection as an effort to control EGT and protect components of the engine.  This richer target will cause a cooling effect serving to protect the exhaust components and, in many cases, produce more torque.  So you'll see the car typically running lean on the street (and hypothetically as clean as possible) but as soon as you drive the car hard (on the track, etc.), and the exhaust (and catalyst) warms up, it begins to change to target the richer fuel targets.  In our experience, the stock fuel tables and control systems were perfectly sufficient to make extra power and torque needed for our OTS maps. 

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