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Practical Reflash Tuning: Ignition Timing

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Ignition Timing

08.01

00:00 - The way an engine responds to ignition timing will be the same, regardless of whether you're tuning a standalone ECU or reflashing a factory one.
00:08 As with the fuel tuning, in most instances, tuning the ignition timing via reflashing is actually relatively straightforward and quick to achieve.
00:19 This is because we will already be starting with a very thorough ignition map as a base to work from, and unless you've made dramatic changes to the engine, you'll typically be able to focus most of your effort on tuning the wide open throttle areas of the engine operation.
00:37 Before you attempt to tune the ignition timing it's important to have a solid understanding of how your particular ECU controls ignition advance, as well as how it handles knock control and knock feedback.
00:52 This is discussed in basic terms in the knock control module but we'll go into specific details in the worked example section.
01:02 Tuning the ignition timing requires logging the current ignition advance, the current engine load, and RPM, as well as any particular knock feedback that's specific to your ECU.
01:16 The load and RPM are essential so that we know exactly where in the ignition timing map the ECU is accessing at any point, while the knock feedback will let us know if the ECU is detecting knock.
01:30 While the knock detection strategies in most late-model OE ECUs are excellent, I always recommend confirming the ECU is accurately detecting knock, using audio knock detection equipment initially.
01:45 Once you're comfortable that the ECU is doing this correctly, we can then rely on the data-logging.
01:51 Since we can usually focus on the wide open throttle area of open-loop operation, when optimising the ignition timing, we can often focus solely on doing this tuning during full throttle ramp runs.
02:05 The process is to perform a run ensure that no knock is present, add some timing, and then repeat the process to assess the effect on engine power and torque.
02:19 Providing no knock is logged during the run, I'll begin by adding two degrees of advance to the entire range of the ignition map that the ECU map is accessing during the ramp run.
02:32 This is where the logging is essential as we need to know the load point at each RPM range so that we can decide where to make our changes.
02:41 If we see a positive change in the engine power and torque from adding this timing, this indicates that we've been moving towards MBT timing and providing no knock occurs, we would continue adding more timing.
02:56 The aim is to optimise the ignition curve until we either reach MBT timing, in which case we'll see the torque plateau, or alternatively, we start encountering knock.
03:09 In this case the engine is said to be knock limited and we need to retard the timing in any area where we logged knock, to prevent that knock from occurring.
03:20 I like to keep a safety margin of approximately two to three degrees from the onset of knock so I'll retard the timing in these areas to achieve this margin.
03:32 If we add timing and find that we've seen no improvement in power or torque at a particular point in the rev range, then this means that the timing was already at MBT and at that point we would remove the extra advance before our next test, as it wasn't beneficial.
03:51 If you're tuning a turbocharged engine then the process is to begin tuning the ignition at the lowest boost level, and hence engine load, possible, normally the wastegate spring pressure.
04:04 Once we have the ignition timing optimised through this load range, we can begin stepping the boost up, until we reach our desired boost target, optimising the ignition table as we go.
04:17 In this way we can be sure that, regardless of the load and RPM, the ignition timing will be optimal.
04:24 I've said that we can focus our energy for the most part on the wide open throttle operation of the engine, and this is true.
04:32 Unless we've made dramatic changes to the engine's mechanical design, then the factory ignition map in the idle and cruise areas is normally going to be very close to ideal.
04:44 It's also very difficult to perform steady state ignition tuning on a factory ECU, and this offers the ability to live-tune the ignition table.
04:54 For these reasons, if the engine isn't suffering from knock in the closed loop areas of the ignition table, we can normally leave them as they are.
05:04 In some instances this might mean that the timing isn't quite optimised to MBT, however for an engine configuration that's still relatively close to standard, we're going to be very close.
05:18 What I do recommend however, is to perform some logging under normal operating conditions such as cruise, and light acceleration, to confirm no knock is occurring in these areas.
05:31 If your logger has the ability to create a histogram of knock versus load and RPM, this is a great way of identifying areas of the ignition map that are over-advanced, and we can then use the histogram to very accurately highlight the areas that need to be altered.
05:50 When we're making changes to the ignition table I recommend maintaining a smooth shape and limiting the change in ignition advance between two adjacent cells to no more than four to five degrees.
06:04 If you have large changes in ignition timing between adjacent cells, this can cause erratic driveability as the engine transitions through these cells.
06:16 It's not uncommon to find in some instances that a completely stock engine is suffering from knock, while running on a standard factory tune.
06:27 In reality this probably indicates that you're operating on a fuel with a lower octane rating than the one that the engine was initially designed for, but many manufacturers will accept this and rely on the knock control system to prevent long term engine damage.
06:44 When faced with this situation it can be hard to see how we can improve performance, when the timing is already over advanced.
06:53 The key here is to actually reduce the timing in the main timing maps, to prevent the knock occurring.
07:02 We don't want knock occurring as it can be damaging to the engine, but the other aspect of this is we can also actually improve engine performance.
07:12 The reason for this is that the factory knock control system will be constantly retarding the timing in the light of a knock event occurring.
07:21 The result is an ignition timing that's quite erratic, and immediately after a knock event, it may also be retarded further than necessary, negatively affecting engine power.
07:34 This erratic timing curve can make the engine feel hesitant and unresponsive and often we can see the result of the knock retard with a dyno plot that is erratic and jumpy.