Engine Control Unit (ECU) / Power Chips (K Series cars)

There are a few variants of ECU used in K Series cars. Most Series 1 cars use the Rover MEMS ECU as also found in MGF's (and therefore readable by MGF garage diagnostic tools).

The stock ECU (particularly the MEMS) is a sealed unit that cannot be adjusted in any way. Options for tuning vary in cost/complexity and therefore performance.

• At the lowest end of the spectrum is something little more complicated than a resistor. The resistor is placed between the ECU and any number of sensor including air temperature, air pressure etc. This 'fools' the ECU into thinking there is a change in the running conditions and making a suitable fuelling and ignition change. The trouble with this solution is that the effects are held within the ECU and it is difficult to know exactly what is happening in any situation. In a worst case the change has the potential to be catastrophic.
• In the mid-range price bracket there are replacement chips (depending on the ECU used). These are bought from 3rd party suppliers and have settings suitable for performance enhanced engines. These can be an improvement, particularly if you have paid for the chip to be made specifically for you via a mapping session. However, in the worst case the adjustments are for a 'generically' improved engines and not suitable for your engine, or at best case are very effective for your current state of tune but need to be re-purchased if you make a significant change in the future.
• In the upper mid-range are piggy back ECU's. These plug between the standard ECU and car and alter the timing based on user configurable demand. Dynajet offer such a system that is proving very popular on motorbikes. The only problem with these are that the cost of such a system is approaching that of fully mapable and most optimal ECUs.
• The ultimate change is a fully programmable / mappable ECU. This replaces the standard ECU and gives the user complete control over ignition and fuelling under a range of conditions. In theory any aftermarket ECU can be used, although many will require an interface loom to be manufactured and may not support all the functions such as the stock Lucas 5AS engine immobiliser used on the Elise. For this reason the Emerald M3DK ECU is the most popular - it quite literally plugs in instead of the standard unit and replicates all the functionality. It's popularity means that engine maps for most popular combinations exist therefore meaning that the car can be used before being fully mapped, and/or that mapping the engine is easier.

The consensus is that in an otherwise standard car a replacement ECU is of little benefit (and by parallel that simple aftermarket kits will offer little benefit). However, as the modifications become more extensive the performance improvements become more pronounced. With highly modified engines the standard ECU is incapable of correctly controlling the engine at all and therefore an aftermarket fully programmable ECU becomes a requirement.