Fact – IN CHIP TUNING THERE IS NO SUCH THING
For any formally qualified automotive/calibration engineer the reality of ‘custom remap’ debate is ignorant and frustrating for a number of reasons;
Firstly – . After 2004 most engine management systems became a closed looped torque based model simply put, the engine management is adapting (optimizing) the tune of the engine in almost real time based on the hard code or what is known as the statistical dynamics element of the memory. A quality remapping engineer understands and respects this and simply enters the correct desired targets in the correct places to the code and the system references the sensors accordingly (closed loop or PID) thus using these settings to achieve the desired result. The one and only time a ‘custom’ strategy is required is when a vehicle is modified to a point where the dynamics employed by the factory ECU are no longer valid for example – a larger turbo is fitted requiring new PID loops to be employed.
Modern torque based engine management systems are way beyond in technology and calibration terms to some guy mapping fuel and boost tables on a dyno cooling with a carpet blower. An engine is a air pump driven by the heating of air from a relative dew point to a maximum permissible EGT. More expansion = more power.
Think of an ECU in its simplest form, it’s a calculator programmed to receive values in terms of voltages and frequencies at a rate of 1 to 200 HZ or in layman’s terms 1 to 200 times a second dependent on the type of value it needs to sample. For example – sensor values such as coolant temperature, are a slow changing value, so a sample of 1-5 HZ is fine. Where fast changing variable’s such as manifold pressure, It requires a faster sample rate of say 50 HZ or 50 times a second. The processor then first of all references (for the sake of this explanation) three memory models within the ECU, one known as ‘statistical elements’ and the others as we know them as ‘maps’ and ‘curves’
Statistical elements
This is the core structure of the ECU function – It can be made up by a number of control algorithms such as ‘Motronic’ and elemental rules such as ideal gas law, this also includes configuration switches and curve/map address library for the controller to switch between based on the strategy or mode required.
Curve
The curve structures in the ECU are a vital and are often mistaken as torque limiters by ‘CUSTOM MAPPERS’ or re-scaled in a effort to bypass a mechanical limit resulting in a loss of resolution and refinement. An ECU can only interpret what a engine is doing by its input signals via the relevant sensors. This is usually done by voltage or frequency – so the ‘curve’ is the real world signal conversion to a digital value the ECU can use in a calculation to out put to its PWM’s
Map
Basically a data matrix, a table of data values arbitrated to a output of the ecu drivers or PWM’s referencing values such as requested torque, boost, lambda and air flow. These are desired targets based on the data and control logic influenced by the ‘curve’ and ‘statistical elements’. ALL employing PID control – understanding this will expose the ignorance of most chip tuners time and time again we see duration loaded calibrations with no adjustment of lambda, just one of many contradictions suffered.
A correctly calibrated ECU will ‘custom tune’ an engine down to the millisecond – the clue is in the name ‘Engine Management’
Turbochargers suffer greatly from tuning ignorance, and are a fundamental component in managing the efficiency of a engine. The compressor map of a turbo dictates the dynamics of the air heating process with the cylinder temperatures vs EGT calibrated precisely known as the ‘flame wall’ as diesel fuel ignition timing is dictated by the mass vs relative fuel temperature respecting thermodynamic variables / eg – the fuel pressure (endothermic reaction), fuel mass (duration), start of injection (timing). We see issues with calibrations where the mass (duration) is modified the SOI (timing) is modified along with increased rail pressure resulting in the movement in flame wall causing a cascade rise in EGT thus damaging the turbocharger due to the pardox of increased boost pressure only compounding the issue. Another issue born out of over fueling and flame de-tuning is the sooting of the exhaust wheel of the turbo causing a imbalance of the turbine and jamming of a variable geometry where applicable thus greatly reducing the life of the turbocharger.
