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Practical Diesel Tuning: Torque Management

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Torque Management

03.54

00:00 - Regardless whether you're tuning a diesel or a gasoline engine, the majority of modern factory ECUs are now what is referred to as torque based ECUs.
00:08 And it's important to understand how these ECUs work so that we can approach tuning them in the correct way.
00:13 Traditionally factory ECUs have used driver throttle position as direct translation to the amount of power and torque the engine produced.
00:19 Looking at gasoline engines for a moment, there was no real way around this back when the throttle body was directly connected to the driver's pedal via mechanical cable.
00:27 The advent of drive by wire throttle however gave the OE manufacturers a lot of flexibility as to how the throttle on the engine responded in relation to what the driver's foot was doing.
00:36 Torque based ECUs will include a table or a set of tables that are usually referred to as driver demand tables.
00:42 These are three dimensional tables with driver pedal position on one axis and RPM on the other.
00:47 These tables are populated with our desired torque values for a given combination and typically you want these numbers to be pretty realistic compared to the actual torque our engine is capable of producing.
00:57 In particular, this table allows a lot of control over the feel of the engine.
01:00 Or how much torque is being produced at part throttle.
01:03 On a gasoline engine, increasing the torque request at lower accelerator pedal positions results in the throttle body opening more quickly and leading to a sense of more part throttle torque.
01:13 On diesel engines the same effect is achieved by providing more fuel quantity at lower accelerator pedal positions.
01:20 There's a few aspects we need to be mindful of if we're going to try to adjust the accelerator pedal position feel.
01:24 Firstly, there is no right setting here as this is very much down to personal preference, so experimentation is really the key.
01:31 Having said that though it can be also very easy to make dramatic changes that make a vehicle difficult or even dangerous to drive so I recommend making small changes and testing the results until you've got the thing sorted out and the response you want.
01:43 It's also important not to make changes to these driver demand tables at the zero percent accelerator pedal position.
01:49 Otherwise, you risk the engine RPM not returning to idle.
01:53 This is obviously a problem in itself however if you're driving on the road and the vehicle doesn't slow down when you back off the throttle, it can be very dangerous.
02:01 Once the driver demand table is properly setup, the ECU then uses this table to decide on the required fuelling and boost pressure to actually deliver that amount of engine torque.
02:10 In the case of a diesel engine, this will typically be interpreted in a separate table that defines delivered fuel quantity with torque on one axis and the RPM on the other.
02:19 One of the issues we may face with tuning a torque based ECU is that usually our intentions are to make more torque from the engine.
02:25 In some cases, the factory torque tables may become a limitation.
02:28 What I mean is that, we take an engine that develops 1000 newton metres of torque in stock form and we increase the engine torque to 1200 newton metres.
02:36 We're also going to want to appropriately scale the rest of the ECU tables so that we're allowed to reach that 1200 newton metres.
02:43 Otherwise, if the calculated torque exceeds the numbers in the torque tables the ECU can simply halt our fun.
02:49 If we don't know what's happening here, this can be immensely frustrating as it's not always immediately obvious that the torque limiting is occurring.
02:55 Most torque based ECUs also have a number of torque limit tables or parameters which you may need to increase in order to make sure you're not running into these at full power.
03:04 This does need to be approached with a little bit of common sense as occasionally these torque limits will be there to protect components such as the transmission or the differential from damage from excessive engine torque.
03:13 Since many factory diesel engines can produce enough torque to damage factory torque converters and clutches, just through an aggressive tune, we obviously need to pay attention to the limits of the drivetrain components.
03:24 These limits will depend on the specific vehicle you're tuning but it's always a good idea to start by researching what the known failure points and component limits are in order to ensure you stay below this level of torque.
03:33 Depending on the ECU you're tuning you may also find that there are various torque limits or backdowns included for engine safety.
03:40 These include coolant temperature, exhaust gas temperature, baro and fuel temp base limits.