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With BMW’s long history of extracting the best from a car with its Motorsport division, one might be excused for thinking it’s going to be tough for independent tuners to find much more – but UK specialist Iain Litchfield has done just that, with the assistance of World Touring Car champion Rob Huff at the wheel.

The result can be seen in the Litchfield BMW M4 on the Akrapovic stand at the Autosport International Show at Birmingham’s NEC.
Off the shelf, the latest F82 BMW M4 is a finely-honed machine that ticks all the right boxes by being faster, more powerful at 425 hp, lighter, and dare we say greener, than the outgoing E92 coupe. Both the M4 and closely related M3 enjoy the return of the famous 3.0-litre straight six engine with the addition of a brace of single-scroll turbochargers.

But some experts reckon that the new M4 misses the mark slightly, particularly with regard to its on-the-limit chassis composure, so Gloucestershire-based world-class tuner Litchfield and Huff, his R&D buddy and ace driver, combined to get to the root of these issues and engineer solutions.

The result is a 25 per cent power boost to 535 hp with the diaphragm-thumping soundtrack of the Akrapovic exhaust system plus enhanced feedback and control for the enthusiastic driver to enjoy.

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Work began on the M4 with a return to Germany for a thorough analysis of its handling and performance at the Nurburgring.
Litchfield proprietor Iain Litchfield explained: “I found that the standard car worked well up to a point. It had decent ride quality in the suspension’s Comfort mode, and on the first few laps of the ’Ring in Sport and Sport + modes it appeared to perform very well.
However, as my confidence grew I felt the suspension lost composure and struggled to keep up at anything over eight-tenths commitment.”

Back in the UK, Iain’s criticisms were confirmed around Silverstone circuit by World Touring Car champion and R&D buddy Rob Huff. Litchfield said: “Rob found exactly the same inconsistencies and also highlighted how critical tyre pressures were to get the balance right.

“We decided that the rebound control of the dampers wasn’t fast enough when pushed, an issue compounded by the M4’s electronically activated rear differential. Essentially, the differential was far quicker to react than the suspension, which made the chassis feel unsettled and the driver less confident of the car’s reactions.”

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Precise data-logging of the BMW’s adaptive dampers confirmed Iain and Rob’s seat-of-the-pants assessments – internal valves that were simply unable to keep up with the stream of commands issued by the car’s ECU.

Damper reaction time was found to be 30 milliseconds, which sounds fast but is ten times slower than a fly’s wing flap, and that each change in damping control could only be initiated when the damper is momentarily static at the end of its travel.

Working with Litchfield’s suspension specialist, the Gloucestershire tuner has developed a suspension solution that works in perfect harmony with BMW’s control systems. The new internal valve in the damper reacts five times faster than the OEM valve, now at just six milliseconds, and the setup can action each change in force immediately, irrespective of the damper’s position in bump or rebound stroke.

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Complementing the hi-tech dampers are new custom-rate springs tuned to cope with the faster reactions for improved body control at speed while engineering in a broader difference in the three suspension modes, making Comfort more appropriate, while Sport and Sport + are better at resisting body roll and pitch.

For the power boost Litchfield made the first UK fitment of the super-lightweight awesome sounding titanium Akrapovic Evolution exhaust system with carbon trims around the quad tailpipes perfectly framed by Akrapovic’s bespoke carbon fibre diffuser.

Litchfield’s dynamometer confirmed the Evolution system’s reduced back pressure benefits with power peaking 52 hp higher at 477 hp. Litchfield then further optimised the engine through an ECU remap, with continued fine tuning pushing the power up to 535 hp and 657 Nm torque, making this M4 even more mouthwatering!

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