Re-maps - The Basics

What is re-mapping?

Re-mapping is referred to software changes in the engine mangement control unit usually called ECU.

The ECU collects data from the all the different sensors up to several thousand times a second. This data is then processed and referenced to the different mapping tables in order to get for the load on the engine at the relevant rpm the right ignition timing and amount of fuel each cycle and additionally the boost control for the modern turbos.

Factors influencing the map

Ambient air intake temperature: It is important because the hotter the air the the less oxygen it containes by volume, which means a reduction in fuel is needed when ambient temperature rises and a lower temperature requires more fuel to maiontain the same level of richness. The air temperature sender takes care of this.

Ambient humidity: Humidity aids combustion and the higher the humidity is the more power the engine will produce with the relevant fueling. No specific sensor is allocated for it, but lambda sensor, knock sensor and possibly the AIT sensor will pick up on this.

Ambient air pressure or barometric pressure: The ambient air pressure is one factor responsible for the amount of oxygen by volume and the barometric pressure is the second one. The higher the barometric pressure the more fuel needs to be injected, giving the car a better performance. Depending on the type of ECU this is catered for by a barometric pressure snsor or by the MAP (Manifold Absolute Pressure) sensor.

Fuel quality: The fuel quality is not only influencing power delivery due to the octane rating but also due to the additive package of different fuel suppliers. This is why power differences are experienced by users when the fuel is changed. To get the best performance out of each fuel it is needed to adjust the ignition timing. The sensor that is coming into place in connection with fuel quality is the knocksensor.

Mixing of different brands of fuel and/or different grades: Mixing different brands of fuel means mixing different additive packages, which can affect each other adversly or enhancing (Mixing Shell Optimax (97 octane) with Shell leaded 4 star (98 octane) in a ratio 1:1 results in 101 octane).

Driving style: Different kinds of driving result in different situations in the combustion area requiring flexibility in the over all running. The maps need to have built in the relevant flexibility.

Insurance requirements: Many underwriters in Europe require a power capping for different cars in order to place them in insurance categories that are suitable for the buyer.


Homologation requirements: In order to fulfill the homologation requirements most ECUs are capped throughout the rpm range. Homologation is one of the worst contributors to the lack of power in a map.

As the map is written to make the particular ECU drivable under all the conditions that we might face on the planet, all the factors are written into the map of each car.

Why re-mapping?

When changing the map (re-mapping or chipping or piggy backing) the idea is to optimise the performance for the standard car. This re-map needs further altering when modifications are done in order to get the optimal performance out of the engine. In either case it is optimised for the local useage.

When it is referred to a generic re-map we usually talking about a re-map that has been done on one car of the same spec and is carried over to any car of this spec when uploading it to the relevant ECU. These generic maps in most of the cases show an improvement, but can sometimes be of little or no effect depending on the production tolerances. These tolerances can be quite substantial. This is why it is advisable to go and do it on the rolling road (I personally would never let anyone come to my door and upload a map this way).

Whether piggy backing, chipping or re-mapping the basic idea is the same.

Some ECUs can't be written to, which means that they either need a stand alone replacement, which is the best but most expensive option in this case or a pigg back. The latter ones usually proove to be rather inefficient and far too costly for the result.

Some ECUs can be chipped, which means that the chip is taken out and replaced or overwritten. Whether it is taken out or overwritten in the ECU does not make a difference to the re-mapping.

Some ECUs can't be chipped because it is virtually impossibly to remove the chip, which can be for different reasons (i.e. gel pack ECU will loose the gel and will be physically destroyed).

Re-mapping is being referred to when the sofware is being loaded up without taking the chip out.

Re-mapping and chipping are essential the same. In both the mapping tables are optimised for improved performance. The mapping tables are an improvement reference data in order to increas/optimise performance.

The difference between a generic map and a custom map is that the custom map is done by evaluating the individual engine rather than the engine type. When optimum performance is required this is necessary because of production tolerances. Some of the door step mappers insist thatthe ECU will adapt, but this is not completely correct.

All modifications to gain performance have one single purpose, which is to draw as much air in as possible. Once achieved it is not only important to get more fuel in, but also to correct the ignition timing, which is an important part of the lengthy custom re-mapping.

A custom re-mapis not necessarily alive re-map. In most of the cases a live re-map on non chipable ECUs is only possible with a special type of hardware, which very few people own.

The advantage of alive re-map is that because it ispossible to simulate the ECU on a laptop that each mapping point can be altered at the same time when tested and the results can be instantly monitored while making the changes.

The same results can be achieved with a non live re-map but will take many times the amount of time and is very impractible to achieve.