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The MG1 ECU uses a model based on a combination of airflow and torque. The model is set up so that a specific airflow is requested in order to hit a requested load%load %. The requested load is a percent of the total load, not engine load, so the percentage scaling only goes from 0-100%.
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There are two different generations of cars within the 2019-2022 range , and both operate using a different strategy.
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Target Cylinder Filling - Load Request, RPM, with an output of Cylinder Filling as z-data
Optimum Engine Torque (moment) - Inverse with airflow as x-axis with torque output as the z-data
Optimum Torque for Function Monitoring - The parallel system for monitoring the torque model and cylinder filling (aka airflow/relative load%load %) and RPM with load%load % (aka torque) as the z-data
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Again, model year is not the hard and fast for identifying this strategy, if . If it doesn’t have a Target Cylinder Filling table itshould , it should just be using the Optimum Engine Torque table instead.
Optimum Engine Torque - Airflow and RPM as axis axes with torque output as the z-data
Optimum Torque for Function Monitoring - The parallel system for monitoring the torque model and cylinder filling (aka airflow/relative load%load %) and RPM with load%load % (aka torque) as the z-data
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Regardless of which version you have, as you increase or change airflow the the entire Target Cylinder Filling / Optimum Torque maps must be rebuilt with the new airflow data assigned across a range of load % (torque) targets and their related airflow at target and airflow at 100% torque. By doing this complex task, you are able to target higher airflow while the vehicle creates the same calculated torque. When you get this correct, boost is well controlled, and the throttle stays open, and there is little to no ignition-based torque management.
After you rebuild the Target cylinder filling and optimum engine torque tables (or in the case of torque model approach 2, the Optimum engine torque table alone), you must rebuild the Optimum torque for function monitoring table so that the monitoring system and the torque model report comparable airflow and torque relationships to the ECU. Failure to do so will result in a hard limp mode.
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Maximum Relative Load tables set the highest percentage of the available load in that area the computer is allowedto allowed to request.
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Meanwhile, Target Cylinder Filling / Optimum Engine Torque determines the target airflow for the given load request, essentially behaving as an airflow model for the car, so this table requries requires some careful tuning.
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Load Control
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, however, is not that simple
On this vehicle the torque and airflow model are very interconnected and limited by other ECU functions.
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As a result, in order to raise what you’re asking for, you’ll need to increase torque targets, driver requests/limits, as well as the drivetrain and wheel torque limits in order to roughly match the increase in torque gained by the increasd increased filling.
Maximum Filling Allowed from Intake Temperature provides a hard limit to airflow and torque so you’ll need to raise these to be slightly above what you’re attempting to hit.
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Managed by the ecu to achieve the airflow request (Cylinder filling). The ECU will simply run the boost necessary to achieve an airflow target (after any temperature or fill limits).
Maximum Boost , and Maximum Intake Manifold Pressure provide a simple ceiling for manifold pressure. It is a very good idea to start these low and gradually raise them as your calibration progresses as they can provide a safety limiter to prevent damaging boost levels. Your final values shoudl should be slightly above what you’re attempting to target so that the driver won’t experience them unless something is wrong.
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Once the limiters are raised, any higher load request% request % will increase desired airflow. The Target Cylinder Filling table sets the relationship between load% load % and Airflow. After rescaling the range of the table it will be able to facilitate higher airflow and more power.
Higher Load Request%Request % (as long as other limiters are also not hit) will increase desired airflow. Target Cylinder Filling describes the relationship between load% load % and airflow. Stock it , the table doesn’t require an appropriate range in order to allow much of an increase in power. In order to make more airflow and power, you’re going to need to scale the table differently to cover the affected areas.
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With these vehicles it is a little bit more tricky in order to create an airflow model given the absence of the Target Cylinder Filling table. In order to increase power you will first need to increase the load target so that the car can achieve it’s intrinsic torque (relative load/request%request %/load%load %). Once you have found this maximum load request there is no mo more effective way to make more power until you increase airflow.
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In the picture above, we have a load request table with the approximate values that equate to maximum load request for a 2022 S5.
The stock Optimum Engine Torque (Moment) doesn’t reference a high enough airflow in order to support the new load request. To rectivy rectify this we’ll need to extend the torque map with a higher value. In regions with higher airflow values, the optimum torque map must make sure to maintain the relationship with airflow and torque requests in order to be happy.
The first part of this is going to be to increase the relative load% load % and the request.
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From the tables above you can see that the request has been increased to match the newer load % appropriately.
The second part of this task is to create a mathematically similar Optimum Engine TOrque Torque for Function Monitoring map. Since the changes are only in the upper load regions, it’s fairly easy. However these changes MUST reflect the same torque and airflow relationships as the Optimum Engine Torque map otherwise you’ll see errors or limp modes occur
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The third and last part is increasing the power. Now that you ahve have a balanced airflow and torque model, you will likely be hitting the intrinsic torque limitations. If your torque model already extends to 100% of the load request, you’ll need to increase the airflow request for a given torque at a given RPM. From there you’ll also need to make sure that the airflow at the request is raised so that the new higher airflow maintains a similar reported torque to the ECU.
As a simple example
Torque request of 50 Load% 50% Load - this is the intrinsic max at a specific RPM. 738*.5 = 369 ft lbs.
The airflow at this load is 120 (relative load %, target cylinder filling).
You desire to raise the power, so you want to increase airflow by 10% at this point.
The new airflow is 132 132% relative load percent.
The new related 100%, load % airflow is now 264 compared to 240.
120 / 240 = 0.5, = 369
132 / 264 = 0.5 = 369
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While fundamentally simple, there are a lot of moving parts to the ignition timing maps for these cars. The Optimum Ignition Timing maps are very carefully modeled stock, and represent the ignition timing under ideal conditions (no knock or heatsoak heat soak etc.) where the car will run the highest output torque. As such you’ll want to leave those completely alone unless you’ve drastically changed physical characteristcs characteristics of the engine internally. Keep in mind as well, that any changes you make to that table will brake break the calculations for the torque model, so you would need to change a large number of tables. In almost every instance, it’s easier to leave these tables alone, and simply use the other tables to calibrate.
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For 93 octane fuels, there is very little reason to change timing if you aren’t drastically increasing load and boost. Typically we’ll only remove a degree of timing or so under high load/rpm RPM conditions.
This ECU uses an Optimum Ignition Timing map, which is under ideal conditions with no variables, that timing equals the amount of torque in the model the car will produce. Because this is under ideal conditions running 100% of this timing is NOT recommended under any circumstances. This also means that it looks at the timing you request under normal conditions and looks at what percentage it is of the ideal timing to understand how much torque the engine will produce. This means that when you reduce timing the car will be aware that the reduction in timing will reduce torque output (and vice versa). In conditions when the torque target is left the same and you reduce ignition timing, the car will change the manifold pressure and airflow request in order to hit your target torque.
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On some vehicles there are per cylinder ignition increase or decrease. This allows you to compensate for particularly knock-prone cylinders with the least amount of impact on torque output. Under light use, these values do not impact the torque calculations as much (or related airflow/boost etc.)
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In order to control the amount of torque produced, the ecu ECU will manage airflow through boost, throttle closures, as well as decreasing ignition timing. A properly tuned vehicle will use minimal throttle closures and will run the average timing from the 4 main timing tables. If the torque is reduced within your power curves despite reasonable manifold pressure and throttle openings, it is very likely that a timing reduction is the root of the issue. Ignition timing changes are highly effective when used to control torque. If this is happening you may need to reexamine your airflow and torque models, as they may not be in line with some of the intrinsic limitations of the torque system or the vehicle.
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Like most other VAG cars, these MG1 ECUbased ECU vehicles use per cylinder knock corrections. These systems, when working properly, are highly active and adaptive. Knock thresholds, gains, increment, increment and decrement rates are all adjustable. With few exceptions we prefer to keep these systems fairly conservative and mostly stock in stock applications.
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Unlike older vehicles, fuel is largely less controllable than most people ahve have come to expect. Many of the early MG1 6 & 8 cylinder vehicles use a fueling approach that counts on the vehicle hitting component protection at wide open throttle. Typically this system swings very rich to cool things down in the engine and then back to lean for clean burn and then possibly back to component protection again later in the pull. This tends to keep the Exhaust Gas Temperatures (EGT) lower overall due to the rich mixture.
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