BMW M4 CSL Stage 3, A World Premiere

We started with stage 1 preparation and then moved on to stage 3. During the development of the mapping, our engineers realised that the ECU software was specific to a CSL and different from a conventional M4, which meant that more time was needed for development. After hours of fine-tuning, we were able to achieve a score of 660 bhp and 800 Nm of torque.

We measured its new performance via our Dragy, with a time of 6.96 seconds from 100 to 200 kph. We also put it up against our two McLarens, the 600LT (600 bhp) and the 570S (800 bhp). But unfortunately, our M4 was no match for them (due to its weight...).

We then moved on to preparing for Stage 3, a much-awaited stage for us. On the programme: installation of hybrid turbos, Eventuri intakes and sports catalysts.

Our aim was to gain around 200 extra horsepower, while slightly increasing torque. We chose not to forge the connecting rods from the M4 CSL, as we wanted to retain as much of its authenticity as possible, which limits us in terms of torque. We also wanted to limit torque in order to preserve traction, which was already complicated with the Michelin Pilot Sport 4S tyres.

When we fitted the Eventuri intakes, we realised that they were not compatible with the M4 CSL as they stood. The reason for this is the chassis reinforcement bar specific to this model, which doesn't leave enough room. So, while we waited for an advanced version specific to this model, we had to find an alternative solution. For the time being, we've opted to fit two BMC sports air filters that fit in place of the original airboxes.

In addition, we fitted sport catalytic converters to replace the original ones, while opting to keep the original particulate filters (DPF) and M-Performance Titanium cat-back.

After fitting the new hybrid turbos, we noticed a 20hp increase in power, but with a later operating range compared with Stage 1. In fact, the mapping needs to be redone to take full advantage of the parts fitted.

So it was time to move on to mapping!

Usually, we work remotely with our engineers based in different parts of France and Europe. We send them the vehicle's map, which they modify and send back to us for analysis on a power bench. However, for this project, we chose to go on site to facilitate communication and resolve problems more quickly.

Mapping

After several mapping tests, we quickly realised that several mechanical parts were going to restrict us from achieving our objectives.

Firstly, the original DPFS, which we had wanted to keep, was far too restrictive. We had to replace them with a complete Milltek line.

Secondly, the injection system was too limited. We decided to keep the original system and adapt to this constraint. We had planned to use an E70 blend, i.e. 70% ethanol and 30% unleaded 98, but in the end we used an E30 blend in order to preserve the pumps.

It took dozens of map changes and hours of work to find the settings that were perfectly suited to our configuration.

The result was 816 bhp and 940 Nm! Admittedly, this is less than the 900 bhp we were hoping for, but it's a coherent score for our current configuration.

Performance

Performance has been greatly improved, with the time from 100-200 km/h in Stage 1 dropping from 6.96 seconds to 5.19 seconds, a gain of 1.77 seconds. To improve our times, we'll have to change to Cup 2 tyres, as the Michelin Pilot Sport 4S won't give us enough traction.

This development will benefit the preparation of our next M2, with which we'll go all the way with the development, forging the engine and installing a much more efficient injection system to reach our target of 900+!

We're proud of the work we've done on this BMW M4 CSL and the performance we've achieved. Despite a number of technical difficulties and limitations, we managed to get the best out of this vehicle while meeting our quality and reliability requirements.

We would like to thank our teams and partners for their expertise throughout this project.