The base car is a 2016 M4 Coupe that Harold bought in early December 2017 with 25,000 miles on the clock. The fact that he added another 10,000 miles in the first eight months of ownership underlines just how much he likes driving it.
You can see his car coming a mile away. While the distinctive Yas Marina blue paintwork stands out from the Miami landscape like a Maybug on a bar room floor it is also the slammed ride height, big wheels, and huge race style rear wing that really grab your attention.
The carbon-fibre aerodynamic components come from more than one source. Velocity Factor supplied the front splitter, front flics, air intake surround frames and side skirts. Apart from the APR Performance rear wing all the other exterior carbon-fibre components are from IND Distribution who also provided the new interior parts.
Sound and Fury
Harold had planned to tune and personalise his new car from day one, and began to action his shopping list once Christmas had come and gone. So five weeks after he had taken over the title his M4 emerged from Active Autowerke with their catless downpipes, mid-pipes, and exhaust tips, the rather weedy factory soundtrack now replaced by a deeper, more purposeful growl.
With the sound fixed and exhaust backpressure lowered the Stage 1 engine upgrade came next, the ECU remap raising boost pressure to 21psi for a useful 555hp at the wheels.
However, the euphoria did not last long and Harold soon returned for the Stage 2 conversion, whose core is a pair of Stage 2 turbochargers from Pure Turbos. These feature larger scroll housings and turbine and impeller wheels, while a more efficient CSF intercooler unit keeps the charge air temperatures within spec on hot Florida days, even with 30psi of boost on tap.
With the exhaust sorted right at the beginning, it was now the turn of the intake side to be uprated. Boosting the airflow upstream of the turbochargers and ensuring minimal obstruction on the journey through the system is the job of the RK Autowerks carbon-fibre intake system and Burger Motorsports aluminium charge pipes.
As there is a practical limit to the horsepower BMW’s M55 bi-turbo straight-six can reliably make on pump fuel, Active’s Mike Hugh discussed the options with Harold, who had 600hp in mind as the absolute minimum figure he wanted to see at the rear wheels.
The decision was taken to add the Burger Motorsports Water Methanol Injection (WMI) System, which involved the installation of ProMeth lines, holders and nozzles like the factory GTS, along with a three-gallon tank. The system is controlled by a Burger Motorsports JB4 WMI piggyback ECU with a map selection facility that allows you to go from factory stock to race tune and anywhere in between at the push of a button on the steering wheel.
With everything installed Active Autowerke performed a custom dyno tune to get the fuelling, spark, boost and other parameters spot on. The result is a staggering 685hp and 923Nm of torque at the rear wheels on 30psi of boost in the Street setting.
The greater stresses imposed during track work where you are on full boost all the time except when braking see the turbo boost dialled back to 24psi for 655hp and 883Nm. It is only the much more efficient intercooling and WMI that allows the engine to produce this kind of power and torque without going into meltdown.
Suspension and Wheels
Making power is one thing, getting it to the ground quite another. Luckily the M4 starts off with a factory carbon-fibre stress bar in the engine bay to stiffen the shell, and has a race bred chassis that is very amenable to upgrades.
As a first play Harold had the car lowered by 30mm using AST uprated springs. This removes the excessive daylight around the 9.5J and 11.0J x 20-inch Brixton CM10 radial forged alloys shod with 265/30ZR20 and 295/30ZR20 Michelin Pilot Sport 4 rubber. The front and rear forged wheels weight 10.8kg and 11.8kg each respectively.
When these had been fitted, Active’s Mike Hugh walked out of his office, took one look at the car and said, “The wheels don’t fill the arches properly, you need spacers!” That is how the car ended up with a set of one-inch spacers and longer wheel bolts all round. Now the wheels and tyres fill the arches to the brim.
A Drive in the Country
Florida has no hills and very few interesting bends on its country roads. But some of those country roads are long and wide, and with low traffic density out of town they can be a relatively safe place to check out the speed of a fast car.
Harold’s M4 has the sort of power and torque that makes it a senseless exercise to try and take standing start figures as the rear tyres would be overwhelmed from the word go.
A rolling start was thus in order and nailing the throttle in second from around 20mph confirmed the worth of BMW’s M differential and the big rear Michelins. Taking the motor to 7,500rpm in second, third and fourth gears was a real riot, with the tail wiggling in second but then hooking up firmly to the tarmac and punching the car down the road with real ferocity.
The way Active has mapped the power and torque curves the delivery feels similar to stock but with nearly 40% more grunt everywhere. This means the car feels perfectly tractable in normal driving, with only the firmer ride a possible issue for those with a delicate constitution. And of course the lower ride height means you need to be more careful around garage ramps and speed bumps.
On the few bends we found out in the country the car felt hunkered down, stable, and well able to deploy its power so long as you are sensible with the throttle. The stock brakes work just fine in fast road use, but we do wonder if they would be marginal on track. Harold says he will upgrade them if necessary.
Speaking of upgrades, Harold has spent US$19,000 on the car in the last six months and is just about to embark on another round of modifications. This latest shopping list includes AST coilovers with separately adjustable ride height, bump and rebound, and external fluid reservoirs.
As he has started doing track days, a Studio RSR bolt-in half roll-cage is also on the list along with a pair of OMP HTE-R race seats with five-point safety harnesses. The final engine upgrade will be a Fuel-It Stage 4 Port Injection/Fuel System.
A work in progress, Harold’s M4 Coupe is a potent road and track weapon right on the edge of what an S55 motor can reliably produce. It is also a testament to Mike and Karl at Active Autowerke who are no strangers to the outer limits of BMW tuning.