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Practical Reflash Tuning: Torque Limits

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Torque Limits

03.47

00:00 - One area that can often cause confusion when tuning a stock ECU is the factory torque limits.
00:07 While not every ECU will incorporate torque limits, it's becoming increasingly common on more modern vehicles.
00:15 Torque limits can be implemented by the ECU in a number of different ways, but essentially they're there in theory to protect the engine and the drive train from excessive engine torque.
00:27 A torque limit may make itself known by way of a fuel cut or ignition cut.
00:33 Or in a more subtle way such as by a drive by wire throttle body simply closing to reduce engine torque.
00:42 If you're tuning an otherwise stock engine, often these torque limits may have no impact on your tuning and you can often extract quite significant increases in engine torque and hence power without ever encountering a torque limit.
00:58 In some instances though, torque limits may be affecting the engine performance even before you begin tuning.
01:06 And in this case you're going to need to address the torque limit if you hope to see any real improvement.
01:13 One of the most common situations where you're likely to exceed the factory torque limit is if you're adding forced induction to a naturally aspirated engine.
01:24 In this case it's reasonable to expect a significant increase in engine torque, or we'd quite rightly be disappointed.
01:32 It stands to reason that one of your first tasks when beginning to tune this sort of combination will be to find and raise or eliminate these torque limits.
01:43 I've also struck situations where the factory engineers have used torque limiting to provide a differentiation between the power output of two otherwise identical engines.
01:56 This can be used for example to give a higher priced and higher spec'd model a power increase over the entry level model.
02:05 I've seen this particular scenario in the GM LS3 V8 engines fitted to the Australian HSV product.
02:15 As an example the 317 kilowatt rated R8 and the higher spec'd 325 kilowatt GTS shared an identical engine package.
02:28 The difference in power was attained simply by employing a torque limit in the R8 model that resulted in the drive by wire throttle closing partially through the middle of the RPM range.
02:42 While in this example the advertised power difference was only eight kilowatts, in reality the mid range power deficit was well over 40 kilowatts.
02:52 The good news for owners of the R8 however, was that by simply removing the torque limit, the power output matched the higher priced GTS.
03:01 While I've just described how the torque limits can be employed to differentiate between two models in a manufacturer's line-up, the flip side of this is that they can genuinely be necessary to prevent engine or drive train damage and hence should be treated with care.
03:20 Due to the wide range of vehicles that this re-flashing course can be applied to, it's impossible for me to advise on what's safe or unsafe for your particular application.