TEST DRIVE: Litchfield BMW M4 Enhancements – From Four to ‘Phwooor’!

BMW M4, Test Drives | July 28th, 2016 by 2
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Is it possible to improve the engineering art of BMW’s Motorsport technicians? A drive of Litchfield’s new M4 demonstrator certainly suggests so… If there were …

Is it possible to improve the engineering art of BMW’s Motorsport technicians? A drive of Litchfield’s new M4 demonstrator certainly suggests so…

If there were any stones left to turn in the development of a new M car, most people would assume that engineers from BMW’s mighty Motorsport division were there analyzing and problem-solving long before the car reached production. Thanks to their efforts, the latest F82 BMW M4 is indeed a finely-honed machine that manages to tick all the right boxes by being quantifiably faster, more powerful, lighter and kinder on the environment than the outgoing E92 coupe. What’s more, the M4 and closely related M3 sibling herald the return of the famous 3.0-liter straight six engine format, albeit with lung capacity expanded by a couple of single-scroll turbochargers.

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While it is not possible to argue with black-and-white statistics, some experts have discovered that on a visceral level the new M4 misses the mark slightly, particularly with regard to its on-limit chassis composure. Admittedly, it has taken the combined efforts of a world-class tuner and world-class racing driver to get to the root of these issues and engineer solutions. But the net result is a car that offers tangible improvements in the areas that get enthusiasts truly salivating, namely feedback and control, while creating an opportunity to raise the hairs on the back of your neck through a more stirring soundtrack.

This, therefore, is the BMW M4 according to Litchfield – a tuned and highly polished version of BMW’s future classic that dials the fun factor up to eleven.

Litchfield BMW M4-3

Work began on the M4 just days after taking delivery of the vehicle, returning it to Germany for a thorough analysis of its handling and performance at the Nurburgring. Litchfield proprietor Iain Litchfield took us through his thought processes during this session.

“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.”

Litchfield BMW M4-53

Litchfield BMW M4-60

Litchfield BMW M4-65

Back in the UK, Iain’s criticisms were confirmed around Silverstone circuit by World Touring Car champion and R&D buddy Rob Huff. Iain reports: “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.”

Precise data-logging of the BMW’s adaptive dampers provided the physical evidence to corroborate Iain and Rob’s seat-of-the-pants opinions – internal valves that were simply unable to keep up with the stream of commands issued by the car’s ECU. Reaction times within the damper were found to be 30 milliseconds, which sounds fast but is ten times slower than a housefly’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.

Litchfield BMW M4-43

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 item, now timed at just six milliseconds, and the setup is able to action each change in force immediately, irrespective of the damper’s position in its bump or rebound stroke.

Joining the high-tech dampers are new, custom-rate springs perfectly tuned to cope with the faster reactions and deliver improved body control at speed. Interestingly, a broader difference has also been engineered into the three suspension modes, meaning that Comfort now strikes a more meaningful definition to the word, while Sport and Sport + offer better resistance to body roll and pitch.

Litchfield BMW M4-35
Litchfield BMW M4-30 Litchfield BMW M4-21

With the ‘body’ now taken care of, Litchfield moved on to tackle the M4’s ‘mind’ and ‘spirit’. The latter is tackled with the UK’s first fitment of the newly developed and super-lightweight Akrapovic Evolution exhaust system. This exquisitely crafted titanium system is such a delight it’s almost a shame to hide it under the car, however there is a welcome flourish at the exit point thanks to carbon trims around the quad tailpipes. Also fitted to this car is Akrapovic’s bespoke carbon fibre diffuser that perfectly frame the outlets.

Far more than just a visual accessory, the sound emanating from the exhaust system strikes the perfect sporty tone: guttural in the mid-range and zingy at the top, without any unwanted drone. In fact, if there was such a job as an exhaust sommelier, that person would already be working at Akrapovic.

Litchfield BMW M4-7

Litchfield’s dyno provides evidence of the Evolution system’s liberating effect on the turbocharged straight six, now peaking 52bhp higher at 477bhp. Isn’t it amazing what a carefully chosen bore diameter and sympathetic routing can do to release unnecessary back pressure.

So good has the exhaust system’s effect been on the latest M powerhouse that Litchfield has used its newfound performance like a relay baton in order to further optimize the engine through an ECU remap. Exhaustive testing and fine-tuning of the car’s ‘mind’ has resulted in a potent combination of up to 535bhp and 485 lb/ft torque. This represents a total increase of 25 percent over standard and yet another level of transformation.

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As an entire package, the Litchfield M4 is both mighty and mightily impressive. Thanks to Iain and Rob’s persistence, we feel that all stones have now been turned and the Munich marque’s latest coupe has the power, control and hard-wired driveability you would expect of its Motorsport badge.

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