What is a remap?

A remap is a change to the software on your car's ECU (Engine Control Unit). The software in the ECU controls everything that your engine does, this includes ignition timing, ignition advance and retard, fuel injection pulse width and turbo boost (not on Pure models unless you have the cycle valve installed). This software has various parameters pre-programmed into it at the factory in the form of a three dimensional map (or 2 dimensional mathematical matrix) this matrix enables the ECU to figure out the engine parameters at varying load and RPMs. An actual map from a City Cabriolet is shown below. This is an unmodified map.

This is a screenshot of some remapping software.

A remap takes the parameters for boost, fuel and ignition timing and changes them according to what the engineer would like the engine to do, usually boost is increased (but not always), ignition timings are advanced slightly more, giving more power but will mean your engine will have to run on higher octane fuel to decrease the likelyhood of knock, and the fuelling is also increased, giving overall more power and torque. The actual changes the engineers of these maps make are closely guarded though, and not all maps are the same, for instance I have been told that certain Stage1 remaps do not change boost levels at all.

The speed limiter can also be removed via a remap as well.

How are remaps made?

First the original software must be downloaded from the ECU on the target car, usually ECUs are built in batches for certain engines and as engine details change through the life of the model series, the ECU software changes slighlty, it may be due to emission regulations, or to get more efficiency from a new component. The software on a smart is write only, you can't read the software through the OBD (on board diagnostics) on a smart car, but you can write new software to it. The only way to get the original file is to crack open the ECU, de-solder the EEPROM that contains the program and place it into an EEPROM reader on a PC. After the original program is downloaded, the engineer finds the maps within using a software program (there are a few out there) and changes some parameters accordingly. (It may also be possible - knowing the CPU used on the ECU - to disassemble the program back into machine code, then recompile it again).

The EEPROM is replaced back into the ECU, and the ECU refitted to the car, the new software is then re-flashed to the EEPROM via the OBD port, and the car then tested on a Chassis Dynamometer for power and torque of the changes made, and any new changes can be made to the original software and re-flashed via the OBD port. The engineer can create several stages of remap according to his wishes, and the originial file can also be used to create custom remaps for customers. Once you have an original file for a particular ECU series (denoted by the numbers on the ECU) any car with that ECU series can then use the remaps that the engineer has created.

How you get your car remapped

You will need to take your car to a company that sells remaps (there's a list of well known remap companies at the bottom of the article). They will check that your car is ok to remap, check which ECU you're using and what you want out of the remap and select the correct remap accordingly, it's uploaded via the OBD port on your car, and it's all over in about 10 minutes. You can get a custom remap, when your car will be put on a rolling road to test the power and torque, your engine modifications will be assessed, and the engine parameters changed to your exacting requirements. Usually if your engine has extensive customisations you'll need a custom remap to get the best out of them.

What a remap does to your car

A remap will increase the power and torque of your car, giving it more drivability, better overtaking, and possibly better fuel economy depending how you drive it. You'll notice that your car accelerates quicker, and the engine will feel 'bigger'.

Which smarts can be remapped?

Almost all smarts can be remapped, with the exception of the petrol forfours (they use Mitsubishi designed engines), this is due to the design of the ECU. The new fortwo also uses the same ECU as the forfour so remapping that could prove problematic.

Issues that can arise

There are some downsides to getting a remap, obviously with more power, the engine will be under more stress, will run slightly hotter, and you will have to change your oil more regularly than without a remap (most people recommend 5000 mile services with a remap). You may also need to run your car on high octane (98+) to get the full benefit of the remap.

[note from spotty badger productions] Following on from the artical about re maps the 44bhp city coupe' Pure is not an easy car to re map. I have had mine done by both Big Performance and Wellsmart but to get the best from the car you really need to change the cycle valve . The cost of the part is only £15 max but it alows more choice of maps.

A list of remap sellers in the UK smart community.

Wellsmart - Sell the Digitec remaps
Smartarse Design - Sell Red-Dot remaps (2 stages, and custom)
Smarts R Us - Sell the Evil Twin remap
BIG - Sell the BIG remap
SW Exclusive - Sell SW remaps

This is not a definitive list, if you'd like to be listed here please email This e-mail address is being protected from spam bots, you need JavaScript enabled to view it