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MoTeC M1 Software Tutorial: Tuning Manifold Pressure Estimate Table

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Tuning Manifold Pressure Estimate Table


00:00 With the M1 using a volumetric efficiency fuel model, inlet manifold pressure is an essential element in calculating the air mass entering the engine.
00:11 While the inlet manifold pressure will normally be derived from the inlet manifold pressure sensor, the M1 also includes an inlet manifold pressure estimate table which can be found in the ‘Initial Setup’ workbook in the ‘Engine Details’ worksheet here.
00:26 There are two uses for this table.
00:29 Firstly if you are running a conventional single throttle body engine and you have selected ‘Automatic’ for the ‘Inlet Manifold Pressure Mode’, the inlet manifold pressure estimate table will be used as a reference if the inlet manifold pressure sensor ever goes into fault.
00:45 If you calibrate this table correctly it will mean that the engine will still perform adequately, although this does get a little more complex if the engine is turbocharged.
00:56 Secondly if you are running a multi-throttle engine and wish to use throttle position for the load axis, this table is used to translate throttle position to an expected manifold pressure.
01:07 In this case configuring this table is essential and there are a few ways that you can approach it.
01:14 The Inlet manifold pressure estimate table is a three dimensional table of engine speed versus throttle position, and the numbers in the table represent the manifold pressure that will become the load reference in the engine efficiency table.
01:29 Probably the easiest example is if we set this table up as a two dimensional table with a direct correlation between throttle position and manifold pressure.
01:39 In this case we can enter the same manifold pressure in the table as the throttle position reference on the load axis.
01:46 First we can bring up the axis setup menu by pressing ‘A’, and disable the ‘Engine Speed’ axis.
01:53 Now at 0% throttle position we can enter 0kPa and at 100% throttle position we can enter 100kPa and perform a linear interpolation.
02:05 This replicates how the older hundred series ECUs dealt with this using throttle position as a sensor for the load input.
02:14 Of course this isn’t very realistic, as first the engine isn’t likely to see 0kPa at zero throttle, and secondly the actual relationship between manifold pressure and throttle position is very non linear.
02:27 If you want, you can accommodate these aspects in the inlet manifold pressure estimate table by developing a more realistic table like this.
02:36 Here you can see we have set the inlet manifold pressure at zero percent throttle to 30 kPa which is probably pretty realistic for an engine with stock cams.
02:46 As the throttle position increases, you can see the inlet manifold pressure rises sharply and has reached 90 kPa by only 40% throttle.
02:56 From here through to full throttle, the manifold pressure rises to 100Kpa.
03:02 This will result in an efficiency table that looks more typical in shape to what we would expect with a conventional engine running a single throttle and plenum.
03:12 The two dimensional table we are currently using assumes that the relationship between manifold pressure and throttle position will remain constant as RPM changes.
03:22 In reality this isn’t the case and particularly at small throttle openings, we tend to see manifold pressure decrease sharply as rpm increases.
03:31 You can chose to ignore this and simply use a two dimensional estimate table, but we do have the ability to enable the RPM axis and create a more realistic table as shown.
03:42 The effect of using a two dimensional or three dimensional table will be on the shape of the efficiency map.
03:50 If you choose to use a two dimensional map, you will find the efficiency table ends up dropping away sharply at low throttle and high RPM, while a properly tuned three dimensional estimate table will have a more regular shape.
04:04 If you are tuning a conventional engine with a single throttle, we can tune the inlet pressure estimate table by using the ‘Q’ key at each site.
04:14 This will set the estimate table to the actual manifold pressure that was being measured at the particular combination of engine speed and throttle position.
04:23 Moving through the table and correctly calibrating each site will yield an accurate estimate table that can then be relied on for good performance should the ECU need to revert to this estimate at any time.

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