The ME Engine Management range uses an advanced ‘Volumetric Efficiency’ (VE) model of the engine's airflow to determine the fueling requirements. This has immense benefits over traditional systems that use a simple pulse-width table, in that any changes to fuel pressure, injector size, or even minor engine changes do not need a complete remap, only adjustments to the engine configuration.

VE simply means how much air is in the cylinder in comparison with how much room there is. So a 2.0 Litre engine with a certain throttle angle might only draw 50% of the total air that it can (i.e. only fill the cylinders to 1.0L of air), hence at this point, the engine would have a VE of 50%. In order to determine the mass of air that is available, its pressure must also be taken into account. This goes to say that the VE table of an engine that has a Manifold Absolute Pressure (MAP) sensor will be significantly different than the one of an engine that only has a Throttle Position Sensor (TPS), as the first dynamically calculates the air quantity, while the latter relies on a static model relating to the position of the throttle plate. Any more fuel would simply go out the exhaust, and any less fuel and we would have air left over - this moves to stoichiometries, whereby with gasoline, we need 14.7 times the amount of air (by MASS) as we do fuel to have a complete burn. (The stoichiometric ratio). Note however that engines may require richer or leaner mixtures to get the best from the engine reliably - no fuel map would ever target 14.7 across all driving conditions!

Essentially, when you map the engine, to a predetermined set of Air-Fuel Ratios (AFRs) you will be ‘reverse engineering’ the engine's airflow potential - its VE.

The engines VE is set mechanically by the hardware (cam profile, port design, exhaust etc) of the engine - more VE = more air = more fuel can be added = more power, so a correctly tuned VE table will have a curve similar to the torque curve of the engine.

There are countless books and guides on understanding a VE model available online, so instead of going into too much detail on this, here are some suggested reading links:

●      Greg Banish’s Book gives a good general understanding of VE and tuning:
https://www.amazon.co.uk/Engine-Management-Performance-How-S/dp/1932494421

●      Bosch’s technical book, while extensive, gives some advanced information regarding EMS
https://www.amazon.co.uk/d/Books/Gasoline-Management-Professional-Automotive-Information/3658039639/


A note on Pressure readings…


When working with the ME221/442 (or most after-market ECUs) the manifold pressure (and if used in Speed Density mode, the resultant engines ‘Primary Load’) is shown in Kilopascals, or kPA.


This is an ABSOLUTE reading, meaning 0 kPa means a perfect vacuum, e.g. in space, and approx 100 kPa means the pressure of the air at sea level (imperially ‘1 Bar Absolute’, or, approx 15 psi absolute).

So, for example, if we were to say we were running 1 Bar (15psi) of BOOST (which is a GAUGE pressure), then we would be running 1 Bar (of atmospheric pressure) plus 1 Bar of turbo-generated pressure - so our readout in kPA would then show 200kPA.


Another example would be to say we were running “half a bar” of boost (0.5 Bar / ~7.5psi) then our manifold pressure reading would be 150 kPa.