Who can explain the MG1 Logic

[whittlebeast]

I am trying to find someone that knows the tuning logic of the MG1 ECU. This is the first 4 sec of a typical hole shot. The top trace has the basic four sensors plus a WOT timer.

The second graph down shows the VE lookup and the resulting AFR. Since AFR is relatively stable, there is no ignition cut active.

Graph 3 indicated there must be a table that is leaning on the spark timing. Desired load and Engine Load are in perfect since indicating Desired Load is a primary control. Torque Request is near 100%, but 100% of what?

Graph 4 has the TPS, as measured at the throttle body, so clearly the torque is being pulled back, making me question the Torque Request comment above.

Who knows and understands how all of these torque limiters tables are controlling this sequence of events. Once the logic is documented, the tuning by tuning companies can begin. Until this happens, it appears tuners are simply guessing.

All of this data is collected with HPTuners and graphed with MegaLogViewer HD.

[whittlebeast]

It looks like the real question it how does the ECU go from the minimum of all of the torque limiters and convert it to Desired Load? Does the ECU then PID to a TPS to converge Desired Load and Engine Load?

[whittlebeast]

This is what Grok claims.

Calculating the **Desired Load** in Bosch ECU tuning, particularly for Motronic systems like ME7, MED9, or MED17, involves understanding the ECU's torque-based control strategy. The Desired Load (often referred to as engine load or relative cylinder fill) is a critical parameter that determines how much air the engine should aspire to achieve the requested torque, which ultimately influences boost, fueling, and ignition timing. Below is an explanation of how Desired Load is typically calculated, based on the principles used in Bosch ECUs:

### 1. **Torque Request as the Starting Point**
- Bosch ECUs operate on a **torque-based control system**, where the driver's input (via the accelerator pedal) is interpreted as a torque request.
- The **Driver Requested Torque** is derived from **pedal maps** (e.g., pedal position vs. engine speed). These maps translate the accelerator pedal position into a desired torque value, often expressed as a percentage of maximum torque or in Nm (Newton-meters).
- For example, in the EcuTek tuning documentation for the VW AG EA855 engine, the pedal maps output a torque request, which is then multiplied by the **Maximum Indicated Torque Maps** for the specific vehicle region, gear, and operating mode (e.g., valve lift).[](https://ecutek.atlassian.net/wiki/sp...ngine%2BTuning)

### 2. **Conversion to Desired Load**
- The ECU translates the torque request into a **Desired Load** (or relative cylinder fill) by using tables such as the **Reference Air Charge** table or **KFMIRL** (Engine Load Desired) in Bosch ME7 systems.
- **Desired Load** is typically expressed as a percentage (%) or in terms of air mass (e.g., mg/stroke). It represents the amount of air the engine needs to achieve the requested torque.
- The ECU uses the **Reference Air Charge** table, indexed by parameters like engine speed, valve lift, and camshaft position, to determine the air mass required. This air mass is then converted into a load value using engine displacement and other calibration factors.[](https://ecutek.atlassian.net/wiki/sp...ngine%2BTuning)

- **Formula for Load (Simplified)**:
In some Bosch systems, load can be approximated using the relationship between air mass flow and engine parameters. For example, a simplified formula from older Bosch systems (like Ford EEC) is:
\[
\text{Load} = \frac{(\text{MAF reading in lbs/min} \times 2)}{(\text{RPM} \times \text{Number of Cylinders})} \div \text{Engine Displacement}
\]
However, in modern Bosch ECUs, the load is calculated internally using more complex models that account for volumetric efficiency, intake air temperature (IAT), and manifold pressure. The ECU uses a **volumetric efficiency map** or **nominal charge map** to refine this calculation.[](https://eectuning.org/forums/viewtopic.php?t=13803)[](https://oldskulltuning.com/moto-mori...-bosch-mse6-0/)

### 3. **Key Maps Involved**
Several maps in the ECU influence the Desired Load calculation:
- **KFMIRL (Engine Load Desired)**: This map defines the desired load based on torque request and engine speed. It?s often inversely related to **KFMIOP** (Map for Optimum Engine Torque), which caps the maximum achievable load.[](https://www.hpacademy.com/forum/gene...-in-bosch-me7/)[](https://blog.uobdii.com/motronic-ecu...ps-and-guides/)
- **LDRXN (Maximum Boost Allowed)**: This map sets the upper limit for load (and thus boost) across the RPM range. For example, in Bosch ME7, boost in mbar can be approximated as:
\[
\text{Boost (mbar)} = (\text{Load} \times 10) + 300 - 1000
\]
So, a load of 160% corresponds to approximately 0.9 bar of boost.[](https://www.hpacademy.com/forum/gene...-in-bosch-me7/)
- **Reference Air Charge Tables**: These tables (indexed by port flaps, valve lift, or cam positions) determine the air mass (mg/stroke) needed for a given torque output. This air mass is used to calculate manifold pressure and boost targets.[](https://ecutek.atlassian.net/wiki/sp...ngine%2BTuning)
- **IAT Correction Maps**: Intake air temperature affects air density, so the ECU adjusts the desired load to compensate for temperature variations.[](https://blog.uobdii.com/motronic-ecu...ps-and-guides/)

### 4. **Boost and Throttle Control**
- Once the Desired Load is calculated, the ECU uses it to determine the **boost setpoint** (for turbocharged engines) or **throttle angle** (for naturally aspirated engines).
- In turbocharged systems (e.g., Bosch MED17), the ECU calculates the required manifold pressure to achieve the desired air charge. This involves the **Boost Setpoint Offset Table** and **Pressure Upstream Turbo Limits**, which ensure the turbo delivers the necessary pressure.[](https://ecutek.atlassian.net/wiki/sp...ngine%2BTuning)[](https://www.hpacademy.com/forum/wino...l-bosch-med17/)
- The ECU may also adjust the wastegate duty cycle or throttle position to achieve the target load, especially in systems like the Bosch MED17.9.63, where boost targets are derived from relative cylinder fill rather than direct pressure targets.[](https://www.hpacademy.com/forum/wino...l-bosch-med17/)

### 5. **Practical Considerations in Tuning**
- **Tuning Desired Load**: To increase performance, tuners often modify the **KFMIRL** or **Reference Air Charge** tables to request higher load values, which results in increased boost or throttle opening. However, this must be balanced with other parameters like ignition timing, fuel delivery, and knock control to avoid engine damage.[](https://www.hpacademy.com/blog/how-t...tuning-course/)[](https://www.hpacademy.com/forum/gene...-in-bosch-me7/)
- **MAF Scaling**: The Mass Air Flow (MAF) sensor calibration must be accurate, as it directly affects load calculations. Incorrect MAF scaling can lead to improper load values, impacting performance and drivability.[](https://www.hpacademy.com/blog/how-t...tuning-course/)[](https://www.reddit.com/r/ECU_Tuning/..._motronic_ecu/)
- **Checksums and Software**: Tools like WinOLS, TunerPro, or EcuTek are used to modify these maps. Tuners must ensure checksum corrections are applied to prevent ECU errors.[](https://www.hpacademy.com/blog/how-t...tuning-course/)[](https://www.vwvortex.com/threads/ong...-1-8t.5496661/)
- **Risks**: Increasing Desired Load beyond the engine?s mechanical limits or without proper tuning of related parameters (e.g., ignition, fuel, or boost limiters) can lead to engine knock, overheating, or component failure. Tuning should be done on a dyno by trained professionals.[](https://ecutek.atlassian.net/wiki/sp...ngine%2BTuning)[](https://www.caracaltech.com/articles...25529176db54c1)

### Summary
In Bosch ECU tuning, Desired Load is calculated by:
1. Interpreting the driver?s pedal input as a torque request via pedal maps.
2. Converting the torque request into a desired air charge (load) using tables like KFMIRL or Reference Air Charge, adjusted for engine speed, valve lift, and cam positions.
3. Using volumetric efficiency and MAF data to refine the load calculation.
4. Adjusting boost or throttle to achieve the target load, with limits set by maps like LDRXN.

For precise tuning, you?ll need to use software like WinOLS, ECM Titanium, or EcuTek to modify these maps, ensuring all related parameters (fuel, ignition, boost) are adjusted accordingly. Always verify changes on a dyno and ensure the engine is in good health before tuning.[](https://www.hpacademy.com/blog/how-t...tuning-course/)[](https://ecutek.atlassian.net/wiki/sp...ngine%2BTuning)[](https://www.hpacademy.com/forum/gene...-in-bosch-me7/)

If you have a specific Bosch ECU model (e.g., ME7, MED9, MED17) or vehicle, let me know, and I can provide more tailored guidance!

[whittlebeast]

More specific to BRP

Calculating **Desired Load** in the Bosch MG1 ECU as used by BRP (Bombardier Recreational Products), such as in Can-Am vehicles with the MG1CA920 or similar ECUs, follows a similar torque-based control strategy as other Bosch ECUs (e.g., ME7, MED17), but with specifics tailored to BRP?s applications, such as turbocharged Rotax engines (e.g., Maverick X3 Turbo). The MG1 ECU is a modern, petrol-focused controller with advanced security features, introduced around 2016, and is used in high-performance recreational vehicles. Below is an explanation of how Desired Load is calculated in this context, incorporating insights from the provided web results and general Bosch tuning principles.

### 1. **Torque Request as the Starting Point**
- The Bosch MG1 ECU in BRP vehicles uses a **torque-based control system**, where the driver?s input (via the throttle pedal or mode selector, e.g., Eco or Sport) is interpreted as a torque request.
- **Pedal Maps**: The accelerator pedal position is mapped to a torque demand, typically via tables that vary by driving mode (Eco, Sport, etc.) and engine speed (RPM). For example, in the Can-Am Maverick X3 with the MG1CA920 ECU, the **Desired Throttle Angle ? Eco** and **Desired Throttle Angle ? Sport** maps define throttle response, which indirectly influences torque demand.[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)
- These maps output a requested torque value, often expressed as a percentage of maximum torque or in Nm, based on pedal position, RPM, and vehicle mode.

### 2. **Conversion to Desired Load**
- The torque request is translated into **Desired Load** (or relative cylinder fill), which represents the air mass required to achieve the requested torque. This is typically expressed as a percentage (%) or in mg/stroke.
- **Key Maps Involved**:
- **Map for Calculation of Nominal Charge**: This map, referenced in tuning resources for BRP?s MG1CA920, calculates the nominal air charge (air mass) needed based on manifold pressure, RPM, and other factors like throttle position.[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)
- **Relative Mass Flow Over Throttle Valve**: This map adjusts the air mass calculation based on throttle valve position, ensuring the ECU accounts for actual airflow.[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)
- **Relative Fresh Air as Function of Manifold Pressure**: This map correlates manifold pressure to the relative air charge, refining the load calculation for turbocharged engines.[](https://oldskulltuning.com/can-am-me...tunerpro-maps/)
- The ECU uses a **volumetric efficiency model** (calibrated for the Rotax engine?s displacement and turbo setup) to convert the torque request into a target air mass. This involves factors like:
- Engine displacement (e.g., 900cc for the Maverick X3 Turbo).
- Intake air temperature (IAT) and manifold absolute pressure (MAP) sensor readings.
- Turbo boost pressure, which is critical for BRP?s turbocharged engines.

- **Simplified Load Calculation**:
While exact formulas vary, the Desired Load can be approximated as:
\[
\text{Load} (\%) = \frac{\text{Air Mass (mg/stroke)}}{\text{Maximum Theoretical Air Mass}} \times 100
\]
The air mass is derived from MAF (Mass Air Flow) sensor data or calculated using MAP, IAT, and volumetric efficiency tables. For turbocharged BRP engines, the ECU adjusts this based on boost pressure targets.

### 3. **Boost and Throttle Control**
- In BRP?s turbocharged applications, the Desired Load directly influences **boost pressure targets**. The ECU uses maps like:
- **Wastegate for Boost Linearization**: Adjusts wastegate position to achieve the target boost pressure, ensuring the desired air charge.[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)
- **Boost Pressure Limiter by Atmospheric Pressure**: Caps boost to prevent overboost, especially at varying altitudes.[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)
- **Boost Pressure**: Defines the target manifold pressure needed for the Desired Load.[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)
- For example, in the Can-Am Maverick X3, a Desired Load of 160% might correspond to a boost pressure of approximately 0.9 bar, calculated as:
\[
\text{Boost (mbar)} = (\text{Load} \times 10) + 300 - 1000
\]
This is a rough approximation and varies with MG1-specific calibrations.[](https://oldskulltuning.com/can-am-me...tunerpro-maps/)
- The throttle valve is also controlled to regulate airflow, using maps like **Desired Throttle Angle** (Eco/Sport), which adjust based on the torque request and operating mode.[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)

### 4. **Specifics for BRP MG1 ECU**
- **ECU Type**: BRP vehicles, like the Can-Am Maverick X3 (model year 2021+), often use the **MG1CA920** ECU, which is a petrol-specific Bosch MG1 variant with enhanced security features (e.g., bench protection introduced in mid-2020).[](https://www.tuningtools.com/bitbox-b...1-bench-module)[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)
- **Tuning Challenges**: The MG1 ECU in BRP applications has been noted for its encryption, making tuning difficult without specialized tools like BitBox or bFlash. Some MG1 ECUs (e.g., post-2020) require unlocking before maps can be modified.[](https://www.maicsonecutuning.com/blo...-ecu-unlocking)[](https://bitsoftware.com/bitbox/catalog/58)
- **Available Maps**: Tuning software like TunerPro for the MG1CA920 provides access to maps critical for Desired Load calculation, including:
- Air calculation: Relative mass flow, nominal charge, and manifold pressure-based air charge.
- Boost control: Wastegate and boost pressure limiters.
- Throttle control: Desired throttle angles for different modes.
These maps are used to adjust the Desired Load to increase performance (e.g., Stage 1 tuning yields +15hp/+15Nm on the Maverick X3 Turbo).[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)

### 5. **Practical Tuning Considerations**
- **Modifying Desired Load**: Tuners increase Desired Load by adjusting the **Nominal Charge Map** or **Boost Pressure Target** to request more air mass, resulting in higher boost and power. However, this requires corresponding adjustments to:
- Fueling: Maps like **Maximum Desired Air-Fuel Ratio** and **Lambda Efficiency** ensure proper air-fuel ratios.[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)
- Ignition: **Spark Advance** maps must be optimized to prevent knock.
- Boost Limits: **Boost Pressure Limiter** and **Wastegate** maps must be raised to allow higher boost.
- **Tools**: Software like TunerPro, BitEdit, or bFlash is used to access these maps. For BRP?s MG1CA920, TunerPro XDF files cost around ?80 and provide detailed map definitions.[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)
- **Risks**: Overincreasing Desired Load without proper tuning can lead to overboost, knock, or engine damage, especially in turbocharged Rotax engines. Dyno tuning by professionals is recommended.
- **MAF/MAP Calibration**: Accurate MAF or MAP sensor calibration is critical, as these directly affect load calculations. Incorrect scaling can cause drivability issues or power loss.

### Summary
In the Bosch MG1 ECU (e.g., MG1CA920) used by BRP:
1. The **torque request** is derived from pedal maps (e.g., Desired Throttle Angle ? Eco/Sport) based on driver input and mode.
2. The torque request is converted to **Desired Load** using maps like **Nominal Charge**, **Relative Mass Flow**, and **Manifold Pressure-Based Air Charge**, adjusted for volumetric efficiency and turbo boost.
3. **Boost pressure** and **throttle angle** are controlled to achieve the target load, using maps like **Wastegate for Boost Linearization** and **Boost Pressure Limiter**.
4. Tuning involves modifying these maps to increase Desired Load for more power, but requires careful adjustment of fueling, ignition, and boost limits.

For BRP-specific tuning, tools like TunerPro with XDF files for the MG1CA920 are recommended, but post-2020 ECUs may require unlocking due to enhanced security. Always verify changes on a dyno and ensure the engine and turbo are in good condition.[](https://www.maicsonecutuning.com/blo...-ecu-unlocking)[](https://oldskulltuning.com/can-am-ma...tunerpro-maps/)

If you have a specific BRP model, ECU variant, or tuning goal, let me know for more tailored advice!

[whittlebeast]

Here is a sample data log as collected by HPTuners and graphed with MegaLogViewer HD. On the two bottom traces, you can see the correlation between the channels.

[JT_alex]

I am trying to find someone that knows the tuning logic of the MG1 ECU. This is the first 4 sec of a typical hole shot. The top trace has the basic four sensors plus a WOT timer.

The second graph down shows the VE lookup and the resulting AFR. Since AFR is relatively stable, there is no ignition cut active.

Graph 3 indicated there must be a table that is leaning on the spark timing. Desired load and Engine Load are in perfect since indicating Desired Load is a primary control. Torque Request is near 100%, but 100% of what?

Graph 4 has the TPS, as measured at the throttle body, so clearly the torque is being pulled back, making me question the Torque Request comment above.

Who knows and understands how all of these torque limiters tables are controlling this sequence of events. Once the logic is documented, the tuning by tuning companies can begin. Until this happens, it appears tuners are simply guessing.

All of this data is collected with HPTuners and graphed with MegaLogViewer HD.

it sound like we have the same problem , WOT!!!

[whittlebeast]

I have no idea if people are using other software to modify limiters to open additional tables, compared to what I am seeing in HPTuners.

[activejetsport]

Good info!

[whittlebeast]

I think I nailed the tune. It gets full throttle all the way up to 8400 RPM. AFR looks great. Timing is totally stock by design. I have been 93 fuel, but you never know when 91 may be the only choice. Right now, I am showing 80 on the dash with over 1/2 tank of fuel, 200 LB rider and not trimmed all the way up. The ski is totally stock.

[whittlebeast]

I asked Grok How is Load calculated in the Bosch MG1 on a BRP version of the MG1

The load calculation for the Bosch MG1 ECU in the Sea-Doo 325 engine (Rotax 1630 ACE, supercharged, 325 hp) follows similar principles to those in automotive MG1 systems but is adapted for the unique demands of a marine personal watercraft (PWC) application. The differences arise from the engine’s design, operating environment, and performance requirements, such as the jet pump propulsion, high-revving supercharged operation, and closed-loop cooling system. Below, I’ll outline how load calculation differs for the Sea-Doo 325 engine compared to a typical automotive Bosch MG1 application (e.g., BMW B58 or Audi TFSI engines).

### Key Differences in Load Calculation for Sea-Doo 325 Engine
1. **Marine-Specific Air Mass Measurement**:
- **Automotive MG1**: Typically uses a Mass Air Flow (MAF) sensor or Manifold Absolute Pressure (MAP) sensor to measure air mass, with corrections for altitude, ambient temperature, and variable valve timing (e.g., Valvetronic or VANOS).
- **Sea-Doo 325**: Relies heavily on a MAP sensor due to the supercharged setup and marine environment, where MAF sensors are less practical due to water ingestion risks and rapid throttle changes. The MAP sensor measures intake manifold pressure, which is critical given the high boost levels (up to 1.5 bar or more) from the redesigned supercharger with a larger intake and smaller impeller.[](https://www.jetdrift.com/sea-doo-engines/)
- **Difference**: The Sea-Doo ECU prioritizes boost pressure data over raw air mass flow, as the jet pump’s instantaneous load response requires precise control of supercharger output. The ECU uses maps like **“Boost pressure target”** and **“Compressor efficiency”** to calculate air mass, with fewer corrections for altitude since PWCs operate near sea level.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)

2. **Simplified Load Formula**:
- **Automotive MG1**: Load (often expressed as injection time in milliseconds for lambda = 1) is calculated using a formula like:
\[
T_L = \frac{Q}{n \cdot K}
\]
Where \( Q \) is air mass flow (kg/h), \( n \) is engine speed (RPM), and \( K \) is the injector constant. This is adjusted by complex factors like volumetric efficiency, knock control, and variable cam timing.
- **Sea-Doo 325**: The formula is similar but simplified due to the Rotax engine’s fixed valve timing and high-revving nature (up to 8250 RPM). The ECU focuses on:[](https://www.jetdrift.com/sea-doo-engines/)
\[
T_L = \frac{Q_{\text{boost}}}{n \cdot K}
\]
Where \( Q_{\text{boost}} \) is the air mass derived from boost pressure and throttle position, reflecting the supercharger’s contribution. The injector constant \( K \) is tuned for marine-grade fuel (regular unleaded, 87 octane) and high-flow injectors optimized for the 325 hp output.
- **Difference**: The Sea-Doo calculation emphasizes boost-driven air mass over volumetric efficiency, as the jet pump’s load is more transient and less dependent on steady-state conditions. The ECU also uses fewer knock corrections due to the engine’s robust plasma-coated cylinder liners and closed-loop cooling, which reduce detonation risks.[](https://www.jetdrift.com/sea-doo-engines/)

3. **Jet Pump Load Dynamics**:
- **Automotive MG1**: Load is influenced by drivetrain resistance (e.g., transmission, wheel torque), requiring torque management maps to balance power delivery across RPM ranges.
- **Sea-Doo 325**: The jet pump introduces unique load characteristics. Unlike a car’s drivetrain, the jet pump’s impeller load varies with water resistance and throttle input, leading to near-instantaneous RPM spikes (0-8250 RPM in seconds). The ECU uses maps like **“Throttle body air mass”** and **“Pump load compensation”** to adjust load based on impeller speed and water flow.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)
- **Difference**: Load calculation accounts for the jet pump’s non-linear resistance, which requires rapid air-fuel ratio adjustments to prevent bogging or over-revving. The ECU prioritizes midrange torque (where PWCs spend most time) over low-end torque, unlike automotive systems that balance across a wider range.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)

4. **Supercharger and Boost Control**:
- **Automotive MG1**: Turbocharged engines (e.g., BMW B58) use wastegate or variable geometry turbo maps to regulate boost, with load limited by overboost protection and knock feedback.
- **Sea-Doo 325**: The supercharged Rotax engine uses a fixed-ratio supercharger with a redesigned larger intake and smaller impeller, spinning at higher RPMs for increased boost. Load calculation integrates:[](https://www.jetdrift.com/sea-doo-engines/)
- **Supercharger efficiency maps**: Ensure optimal air delivery without cavitation.
- **Boost ceiling maps**: Cap air mass to protect the engine at 8250 RPM.
- **Throttle-by-wire**: Precise control of air charge via electronic throttle, critical for PWC’s rapid acceleration (0-60 mph in 3.4 seconds).[](https://sea-doo.brp.com/us/en/models...nce/rxp-x.html)
- **Difference**: The Sea-Doo ECU calculates load with a heavier reliance on supercharger performance, as boost is always engaged (no lag like a turbo). This results in a more aggressive load curve, with fewer safety margins for knock or thermal limits due to the engine’s marine-specific durability features.

5. **Sensor Inputs and Corrections**:
- **Automotive MG1**: Uses a wide array of sensors (MAF/MAP, IAT, barometric pressure, knock, lambda, crankshaft position) with complex corrections for emissions, fuel economy, and drivability.
- **Sea-Doo 325**: Employs fewer sensors, focusing on:
- MAP sensor for boost pressure.
- Intake Air Temperature (IAT) for density corrections.
- Throttle Position Sensor (TPS) for rider demand.
- Lambda sensor for air-fuel ratio feedback (less critical than in cars due to fewer emissions constraints).
- Engine Coolant Temperature (ECT) for closed-loop cooling adjustments.
- **Difference**: The Sea-Doo ECU simplifies corrections, omitting barometric pressure (minimal altitude variation) and complex knock control (marine fuel and cooling reduce detonation). The focus is on real-time throttle response and boost management, with maps like **“Lambda control”** tuned for performance over efficiency.[](https://evopowersports.com/products/...-x-rxt-x-325hp)

6. **Relative vs. Absolute Load**:
- **Automotive MG1**: Distinguishes between absolute load (air mass vs. maximum theoretical capacity) and relative load (percentage of max load based on throttle/boost), used for torque management and driver feedback.
- **Sea-Doo 325**: Primarily uses absolute load, as the jet pump’s direct drive simplifies torque demand. Relative load is less relevant since rider input (throttle) directly correlates with boost and impeller load. The ECU may report relative load for diagnostic tools (e.g., Maptuner Nano), but it’s not critical for operation.[](https://rivaracing.com/riva-sea-doo-...20-215u-b.html)
- **Difference**: The Sea-Doo system focuses on absolute load to match the jet pump’s instantaneous demand, reducing the need for relative load calculations used in automotive torque vectoring or traction control.

7. **Tuning and ECU Lockdown**:
- **Automotive MG1**: Tuning involves modifying maps like air mass, boost targets, and ignition timing, but ECUs are often locked, requiring bench flashing or tuning boxes (e.g., Effective Tuning for VAG cars).[](https://effective-tuning.com/blog/md...on-ecu-tuning/)
- **Sea-Doo 325**: The MG1 ECU is highly encrypted, similar to Can-Am side-by-sides, making tuning challenging. Aftermarket solutions (e.g., RIVA, EVP) offer unlocked ECUs or flash tools (Maptuner Nano, CodeShooter 2.0) to adjust:[](https://www.greenhulk.net/forum/pers...x-325hp-engine)
- **Air mass through throttle body**.
- **Boost ceiling for higher RPM**.
- **Fuel maps for aftermarket impellers or intakes**.[](https://rivaracing.com/riva-sea-doo-...20-215u-b.html)[](https://evopowersports.com/products/...-x-rxt-x-325hp)
- **Difference**: Sea-Doo tuning focuses on maximizing boost and impeller efficiency, with less emphasis on emissions or drivability. The locked ECU limits modifications, but marine applications tolerate higher load values due to fewer regulatory constraints.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)

### Practical Example for Sea-Doo 325
For a 2024 Sea-Doo RXP-X 325 at 7000 RPM with a MAP reading indicating 1.2 bar boost:
- Air mass \( Q_{\text{boost}} \) is estimated at ~450 kg/h (based on supercharger output and throttle position).
- Using an injector constant \( K = 0.008 \) (tuned for high-flow marine injectors):
\[
T_L = \frac{450}{7000 \cdot 0.008} = 8.04 \, \text{ms}
\]
- The ECU adjusts this load value using boost ceiling maps and lambda feedback to prevent lean conditions, ensuring the engine delivers 325 hp without cavitation or overheating.[](https://sea-doo.brp.com/us/en/models...nce/rxp-x.html)

### Key Contextual Notes
- The Rotax 1630 ACE 325 is an evolution of the 300 hp variant, with a higher rev limit (8250 RPM vs. 8000 RPM) and optimized supercharger, affecting load calculation by prioritizing high-RPM air mass delivery.[](https://www.jetdrift.com/sea-doo-engines/)
- The jet pump’s design shifts the torque curve higher in the RPM range, making load calculations more sensitive to throttle transients than in automotive applications.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)
- Unlike automotive MG1 systems, the Sea-Doo ECU does not need to comply with strict emissions standards, allowing more aggressive load values for performance.[](https://evopowersports.com/products/...-x-rxt-x-325hp)

### Limitations
- Exact load calculation algorithms are proprietary to Bosch and BRP (Sea-Doo’s parent company). The above is based on tuning insights and marine engine principles.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)[](https://evopowersports.com/products/...-x-rxt-x-325hp)
- Tuning tools like Maptuner or EVP provide partial map access, but full details of load-related maps (e.g., “Pump load compensation”) are not publicly documented.[](https://rivaracing.com/riva-sea-doo-...20-215u-b.html)[](https://evopowersports.com/products/...-x-rxt-x-325hp)

If you have specific tuning data or a particular aspect of the Sea-Doo 325 engine’s load calculation (e.g., aftermarket mods, impeller changes), I can refine the explanation further!

[RUTHLESS RACING STORE]

i asked grok how is load calculated in the bosch mg1 on a brp version of the mg1

the load calculation for the bosch mg1 ecu in the sea-doo 325 engine (rotax 1630 ace, supercharged, 325 hp) follows similar principles to those in automotive mg1 systems but is adapted for the unique demands of a marine personal watercraft (pwc) application. The differences arise from the engine’s design, operating environment, and performance requirements, such as the jet pump propulsion, high-revving supercharged operation, and closed-loop cooling system. Below, i’ll outline how load calculation differs for the sea-doo 325 engine compared to a typical automotive bosch mg1 application (e.g., bmw b58 or audi tfsi engines).

### key differences in load calculation for sea-doo 325 engine
1. **marine-specific air mass measurement**:
- **automotive mg1**: Typically uses a mass air flow (maf) sensor or manifold absolute pressure (map) sensor to measure air mass, with corrections for altitude, ambient temperature, and variable valve timing (e.g., valvetronic or vanos).
- **sea-doo 325**: Relies heavily on a map sensor due to the supercharged setup and marine environment, where maf sensors are less practical due to water ingestion risks and rapid throttle changes. The map sensor measures intake manifold pressure, which is critical given the high boost levels (up to 1.5 bar or more) from the redesigned supercharger with a larger intake and smaller impeller.[](https://www.jetdrift.com/sea-doo-engines/)
- **difference**: The sea-doo ecu prioritizes boost pressure data over raw air mass flow, as the jet pump’s instantaneous load response requires precise control of supercharger output. The ecu uses maps like **“boost pressure target”** and **“compressor efficiency”** to calculate air mass, with fewer corrections for altitude since pwcs operate near sea level.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)

2. **simplified load formula**:
- **automotive mg1**: Load (often expressed as injection time in milliseconds for lambda = 1) is calculated using a formula like:
\[
t_l = \frac{q}{n \cdot k}
\]
where \( q \) is air mass flow (kg/h), \( n \) is engine speed (rpm), and \( k \) is the injector constant. This is adjusted by complex factors like volumetric efficiency, knock control, and variable cam timing.
- **sea-doo 325**: The formula is similar but simplified due to the rotax engine’s fixed valve timing and high-revving nature (up to 8250 rpm). The ecu focuses on:[](https://www.jetdrift.com/sea-doo-engines/)
\[
t_l = \frac{q_{\text{boost}}}{n \cdot k}
\]
where \( q_{\text{boost}} \) is the air mass derived from boost pressure and throttle position, reflecting the supercharger’s contribution. The injector constant \( k \) is tuned for marine-grade fuel (regular unleaded, 87 octane) and high-flow injectors optimized for the 325 hp output.
- **difference**: The sea-doo calculation emphasizes boost-driven air mass over volumetric efficiency, as the jet pump’s load is more transient and less dependent on steady-state conditions. The ecu also uses fewer knock corrections due to the engine’s robust plasma-coated cylinder liners and closed-loop cooling, which reduce detonation risks.[](https://www.jetdrift.com/sea-doo-engines/)

3. **jet pump load dynamics**:
- **automotive mg1**: Load is influenced by drivetrain resistance (e.g., transmission, wheel torque), requiring torque management maps to balance power delivery across rpm ranges.
- **sea-doo 325**: The jet pump introduces unique load characteristics. Unlike a car’s drivetrain, the jet pump’s impeller load varies with water resistance and throttle input, leading to near-instantaneous rpm spikes (0-8250 rpm in seconds). The ecu uses maps like **“throttle body air mass”** and **“pump load compensation”** to adjust load based on impeller speed and water flow.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)
- **difference**: Load calculation accounts for the jet pump’s non-linear resistance, which requires rapid air-fuel ratio adjustments to prevent bogging or over-revving. The ecu prioritizes midrange torque (where pwcs spend most time) over low-end torque, unlike automotive systems that balance across a wider range.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)

4. **supercharger and boost control**:
- **automotive mg1**: Turbocharged engines (e.g., bmw b58) use wastegate or variable geometry turbo maps to regulate boost, with load limited by overboost protection and knock feedback.
- **sea-doo 325**: The supercharged rotax engine uses a fixed-ratio supercharger with a redesigned larger intake and smaller impeller, spinning at higher rpms for increased boost. Load calculation integrates:[](https://www.jetdrift.com/sea-doo-engines/)
- **supercharger efficiency maps**: Ensure optimal air delivery without cavitation.
- **boost ceiling maps**: Cap air mass to protect the engine at 8250 rpm.
- **throttle-by-wire**: Precise control of air charge via electronic throttle, critical for pwc’s rapid acceleration (0-60 mph in 3.4 seconds).[](https://sea-doo.brp.com/us/en/models...nce/rxp-x.html)
- **difference**: The sea-doo ecu calculates load with a heavier reliance on supercharger performance, as boost is always engaged (no lag like a turbo). This results in a more aggressive load curve, with fewer safety margins for knock or thermal limits due to the engine’s marine-specific durability features.

5. **sensor inputs and corrections**:
- **automotive mg1**: Uses a wide array of sensors (maf/map, iat, barometric pressure, knock, lambda, crankshaft position) with complex corrections for emissions, fuel economy, and drivability.
- **sea-doo 325**: Employs fewer sensors, focusing on:
- map sensor for boost pressure.
- intake air temperature (iat) for density corrections.
- throttle position sensor (tps) for rider demand.
- lambda sensor for air-fuel ratio feedback (less critical than in cars due to fewer emissions constraints).
- engine coolant temperature (ect) for closed-loop cooling adjustments.
- **difference**: The sea-doo ecu simplifies corrections, omitting barometric pressure (minimal altitude variation) and complex knock control (marine fuel and cooling reduce detonation). The focus is on real-time throttle response and boost management, with maps like **“lambda control”** tuned for performance over efficiency.[](https://evopowersports.com/products/...-x-rxt-x-325hp)

6. **relative vs. Absolute load**:
- **automotive mg1**: Distinguishes between absolute load (air mass vs. Maximum theoretical capacity) and relative load (percentage of max load based on throttle/boost), used for torque management and driver feedback.
- **sea-doo 325**: Primarily uses absolute load, as the jet pump’s direct drive simplifies torque demand. Relative load is less relevant since rider input (throttle) directly correlates with boost and impeller load. The ecu may report relative load for diagnostic tools (e.g., maptuner nano), but it’s not critical for operation.[](https://rivaracing.com/riva-sea-doo-...20-215u-b.html)
- **difference**: The sea-doo system focuses on absolute load to match the jet pump’s instantaneous demand, reducing the need for relative load calculations used in automotive torque vectoring or traction control.

7. **tuning and ecu lockdown**:
- **automotive mg1**: Tuning involves modifying maps like air mass, boost targets, and ignition timing, but ecus are often locked, requiring bench flashing or tuning boxes (e.g., effective tuning for vag cars).[](https://effective-tuning.com/blog/md...on-ecu-tuning/)
- **sea-doo 325**: The mg1 ecu is highly encrypted, similar to can-am side-by-sides, making tuning challenging. Aftermarket solutions (e.g., riva, evp) offer unlocked ecus or flash tools (maptuner nano, codeshooter 2.0) to adjust:[](https://www.greenhulk.net/forum/pers...x-325hp-engine)
- **air mass through throttle body**.
- **boost ceiling for higher rpm**.
- **fuel maps for aftermarket impellers or intakes**.[](https://rivaracing.com/riva-sea-doo-...20-215u-b.html)[](https://evopowersports.com/products/...-x-rxt-x-325hp)
- **difference**: Sea-doo tuning focuses on maximizing boost and impeller efficiency, with less emphasis on emissions or drivability. The locked ecu limits modifications, but marine applications tolerate higher load values due to fewer regulatory constraints.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)

### practical example for sea-doo 325
for a 2024 sea-doo rxp-x 325 at 7000 rpm with a map reading indicating 1.2 bar boost:
- air mass \( q_{\text{boost}} \) is estimated at ~450 kg/h (based on supercharger output and throttle position).
- using an injector constant \( k = 0.008 \) (tuned for high-flow marine injectors):
\[
t_l = \frac{450}{7000 \cdot 0.008} = 8.04 \, \text{ms}
\]
- the ecu adjusts this load value using boost ceiling maps and lambda feedback to prevent lean conditions, ensuring the engine delivers 325 hp without cavitation or overheating.[](https://sea-doo.brp.com/us/en/models...nce/rxp-x.html)

### key contextual notes
- the rotax 1630 ace 325 is an evolution of the 300 hp variant, with a higher rev limit (8250 rpm vs. 8000 rpm) and optimized supercharger, affecting load calculation by prioritizing high-rpm air mass delivery.[](https://www.jetdrift.com/sea-doo-engines/)
- the jet pump’s design shifts the torque curve higher in the rpm range, making load calculations more sensitive to throttle transients than in automotive applications.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)
- unlike automotive mg1 systems, the sea-doo ecu does not need to comply with strict emissions standards, allowing more aggressive load values for performance.[](https://evopowersports.com/products/...-x-rxt-x-325hp)

### limitations
- exact load calculation algorithms are proprietary to bosch and brp (sea-doo’s parent company). The above is based on tuning insights and marine engine principles.[](https://www.greenhulk.net/forum/pers...x-325hp-engine)[](https://evopowersports.com/products/...-x-rxt-x-325hp)
- tuning tools like maptuner or evp provide partial map access, but full details of load-related maps (e.g., “pump load compensation”) are not publicly documented.[](https://rivaracing.com/riva-sea-doo-...20-215u-b.html)[](https://evopowersports.com/products/...-x-rxt-x-325hp)

if you have specific tuning data or a particular aspect of the sea-doo 325 engine’s load calculation (e.g., aftermarket mods, impeller changes), i can refine the explanation further!

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