As was the norm with Mercedes-Benz and most German manufactured vehicle. The Mercedes S Class (W140) came with a 155mph speed limiter. The limiter is enforced electronically and removing is fairly straight forward.
The W140 is a superb car featuring fantastic build quality as it should considering it cost over US $1 Billion to develop in the late 1980s/early 1990s.

 

The M120 Engine was Mercedes answer to the BMW V12, it was bigger, more powerful and certainly far more reliable, however it was considerable bigger too.

 

 

We recently removed the Limiter from an S600 V12 vehicle.

There are two major obstacles to removing the limiter:-

  1. The Electronic Limiter on the Engine Management ECU
  2. The Speedo Readout (It stops reading after 160)

 

 

Problem 1:

The M120 Engine in the W140 uses two ECUs. There are two generations of ECU used in the W140 as later models with COP ignition used an updated Motronic unit from Bosch. In all cases the W140 uses Two ECUs, one to control each back.
Above: Early Generation
Below: Later Generation

 

 

Both types of ECU need to be remapped in order to remove the Speed Limiter. When the Limiter kicks in the vehicle will limit the RPM and there is potential for the car running lean. It’s our opinion that this poses a bigger danger than removing the limiter.

 

If you send us the maps or even the ECUs we will be happy to remove the limiter and also add on the later type ECU the Full Throttle Fuel Enrichment which was removed due to emissions laws.

 

Problem 2:

The only solution we are aware of that works correctly is to swap out the cluster to that of a Brabus or AMG model with the 300kmh limit. If someone has access to a Brabus or AMG unit we could be interested in looking at it. Quite possibly its just a matter of altering the software and changing the facia. The Facia could be redesigned quite easily.

 

A Typical W140 Instrument cluster, with a mechanical readout limited to 160

 

 

A Brabus W140 cluster with a maximum mechanical readout of 300kmh (186 Mph)

 

The Result:-

 

Having removed the Speed Limiter from a 1998 S600 W140 V12 with a M120 engine we can confirm that the top speed according to GPS appears to be around 179MPH to 180MPH. On a clear flat road the vehicle perform flawlessly until it redlined the engine. This would indicate that a higher top speed could be possible if one were to change the gear ratios. We may change the rear diff on our S600 but this is something we have not researched.

 

Please bear in mind our test was conducted on a Late W140 with the full throttle fuel enrichment re-added. When the Bosch ECUs were updated Full Fuel enrichment was removed to pass emissions limits being imposed at the time. Without full enrichment then we doubt you could get better than 175MPH.

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