Supercharged Z4 M Coupé / This supercharged Z4 M Coupé will blow you away!
Walk the line
Strapping a supercharged to the already potent Z4 M makes for an exceptional performance machine.
Words and photos Chris Nichols.
Tuning a car is often a fraught process. There’s the stress that comes from buying new products, not knowing if they’ll work until they’re on the car, despite your hours of research. There’s the possibility that the workshop you’ve chosen will do bad work or rip you off. And, of course, there’s the likelihood that fitting upgrades will simply expose weaknesses in other parts of the car you weren’t aware of, forcing you to spend money you hadn’t planned to.
Melbourne, Australia’s Kris Hooper knew about all those potential pitfalls when he chose his 2006 Z4 M Coupé. A tearaway in his younger days, he’d managed to destroy one car and blow two engines in another before getting a 1998 Subaru WRX sedan as his first proper performance car. However, his experience making mild mods to that, coupled with his otherwise methodical thought processes and focus on research, meant when he decided on something European to change things up, he wasn’t going to approach the project with anything other than highly considered plans to ensure he avoided many of those common tuning errors.
“Magazines and forums have taught me how easy it can be to perform a modification only to find you are not happy with the result, to not get enough bang-for-your-buck, or to find further down the track that it is incompatible with something else you have planned.” All this is why, before he even began, Kris had a pretty clear idea as to what he wanted and how to achieve it. The Z4 M base was already a great start – powerful, with great street handling and braking, and looks that Kris fell in love with well before the test-drive. But his desire for a true all-rounder that combined ability on the street with track prowess meant things had to be planned well in advance, particularly as, being such a rare car outside of America, parts were not exactly in huge supply. “Most of the parts I’ve used have come from the US,” Kris says, “simply because the number of E85 Z4s in the States makes production of go-faster bits viable.”
While in some respects, that lack of choice made things easy, Kris still needed to make the right decisions to achieve the goals he wanted, so on top of his research he talked to the guys at SouthernBM, a local and highly renowned specialist shop. The end result was a pretty tasty combination of American tuning parts, such as a 34-row Zionsville radiator, Vibra-Technics engine mounts, a StopTech Trophy BBK, Turner anti-roll bars, Hyperco Linear Race springs, Rogue Engineering rear shock mounts and adjustable rear control arms, and an APR Performance carbon GT wing. In fact, JRZ RS-1 dampers aside, the only brake and suspension parts Kris didn’t get from the US were the Vorschlag E46 M3 camber/caster plates and Carbone Lorraine R6E pads. Even inside, Kris relied on US know-how to help improve the already pleasant Z4 M cabin in the form of beautiful and custommade anti-slip pedals from Ultimate Pedals. To these he added a Recaro Pole Position bucket for himself and a ZHP-style weighted BMW gear knob.
Rather surprisingly, given the S54 engine is from the E46 M3, Kris had trouble finding options even here, specifically in the form of supercharger kits. At the time, only ESS kits were available, so to get the power he wanted Kris had no choice but to go with the company’s VT2-525 blower, intercooler and intake manifold kit. Currently it makes 403whp and 228lb ft of torque. Of course, ESS equipment is hardly second-best, and thanks to upgrading the included Setrab oil cooler for a bigger one, Kris reckons even now, with more options on the market, he wouldn’t change a thing.
Thankfully, Kris’s other engine tuning options were easier to come by. He decided on a beautiful Tekarbon carbon fibre engine cover to spruce up the bay, and a KSS Performance valve-controlled exhaust to allow him to stay street-legal and not annoy his neighbours on those early mornings when he heads to the track yet still enjoy the full metallic scream of the S54 when he gets there. And he’s there a lot.
In fact, thanks to holding onto his WRX for more practical driving, Kris can afford to use the Z4 as almost purely a toy. This freedom, combined with his desire to learn from instructors on a regular basis and to study his own on-board data stats, means he’s able to really enjoy the car at the Marque Sports Car Association (MSCA) sprint days he attends regularly. He actually won his class in both 2014 and 2015.
Not that it’s all been plain sailing on the way to the top. While Kris has generally been very careful to build the car in a holistic way, avoiding many of the pitfalls others fall into, there have been challenges and even a scary on-track moment coming from a rare lapse of judgement when it came to both on-track behaviour and the order in which he fitted his mods. In terms of the challenges, the biggest was getting rid of the stock suspension setup’s on-track understeer. “For a car that handled so well on the street, I wasn’t expecting so much understeer,” Kris says. “An additional strut brace didn’t help. Wider front tyres didn’t help. Additional front camber didn’t help much either. Nor did changing my driving style to add some extra trail braking. It wasn’t until I swapped the suspension to the current coilovers and anti-roll bars and was able to stiffen the rear relative to the front that I was able to get the car to rotate like it should.”
And that scary moment? That was the result of what turned out to be an unwise decision to head to Calder Park, a track with one of Australia’s longest straights, on stock brakes (albeit with nearly new pads) despite having fitted the supercharger kit. Now, in his defence, Kris says the brakes had been ordered at the same time but not arrived before the last-minute spot opened up. We’ll let him tell you what happened next: “Halfway through the day, the pedal was starting to feel a little sketchy, and I began a cool down lap so I could come in and inspect the pad material. Part way into that lap, though, a supercharged Honda Civic tore out of the pits ahead of me, and the red mist descended. About a minute later he was still in front as we hit the main straight. At the end of it, as we were both hitting 220km/h (135mph), some semblance of rational thought returned and I started braking slightly before my marker because of my earlier concerns. Too little, too late. Under my left foot I could feel little more than air. Brake pressure was non-existent.”
As he later learned after pumping a whole extinguisher into the front left caliper, the pad material had just crumbled away by that point, leading to piston seals melting and fluid spraying everywhere. Luckily he still managed to save it, steering the Z4 around the Civic and through the narrow gate at the end of the straight before spinning to slow down in the field beyond. Safe to say, the StopTechs went on straight afterwards!
One additional benefit of fitting the big brakes was that they necessitated a wheel change. Never a fan of the OEM design, Kris had previously chanced upon a forum member running Volk Racing G2s in the same matt black as his own Z4 and decided they were perfect. And, as luck would have it, a member of a different forum who lived locally was selling a set just when Kris needed them. “They must have been the only used set of wheels in the correct fitment available locally at the time, and possibly ever since,” he says. “I was so happy with them that when it came time to get a separate set of track wheels I went straight to Volk, who made me up a set of TE37SLs that, again, are exactly what I wanted.” It’s hard to argue with Kris’s choice, too.
Japanese wheels often look great on BMWs and this is no exception. The relatively rare G2 design’s sharp edges and rounded curves, especially, match perfectly with the E85 Z4 M Coupé’s similar mix of lines, keeping the car looking current and fresh, despite now being ten-years-old. And thanks to Kris’s focus on getting the handling, power and braking right, it’s now a car that doesn’t just look great but one he can enjoy driving for years to come (like his WRX, he has no plans to part with it though).
“The Z4 M, to me, represents a challenge, one that never gets old. There is such a fine line between getting it right and everything going to hell in a split-second. Sprinting along the right side of that line is one of my favourite things in the world.”
DATA FILE #Supercharged
Z4 M Coupé / #ESS
ENGINE AND TRANSMISSION 3.2-litre straight-six S54B32 , #ESS-VT2-525
supercharger kit ( #Vortech-V3Si
intercooler and intake manifold), #K&N
air filter, #Zionsville
aluminium radiator, #Vibra-Technics
engine mounts, #Tekarbon
carbon fibre engine cover, #Bosch-453cc
valve-controlled exhaust with push-button controller, KKS-Performance 4x80mm exhaust tips, software reflash to remove speed limiter and raise rev limiter to 8200rpm, six-speed manual gearbox
CHASSIS 8.5x19” ET+35 (front) and 9.5x19” ET+22 (rear) #Volk-Racing
G2 wheels with 245/35 (front) and 275/30 (rear) Bridgestone Potenza tyres for the street, 8.5x18” ET+35 (front) and 9.5x18” ET+22 (rear) Volk Racing TE37SL wheels with 245/40 (front) and 275/40 (rear) Nitto NT-01 tyres for the track, JRZ RS-1 coilovers with Hyperco Linear Race springs (450lb front, 600lb rear), Turner Motorsport 30/25 E46 M3 anti-roll bars, stock front strut brace, Rogue Engineering adjustable rear control arms, Rogue Engineering rear shock mounts, Vorschlag E46 M3 camber/caster plates and perches, StopTech Trophy Sport BBK with six-pot calipers (front) and four-pot calipers (rear), 355x32mm two-piece slotted rotors allround and stainless braided lines, Carbone Lorraine R6E sintered endurance pads, Motul 600RBF fluid
EXTERIOR Carbon fibre centre grille (sourced by Turner Motorsport), APR Performance rear carbon GT wing, M Power windscreen decal
INTERIOR Recaro Pole Position race bucket (driver’s side only), Macht Schnell Competition Liteweight seat mounts, BMW ZHP-style weighted gear knob, LeatherZ leather door handle covers, custom billet Ultimate Pedals anti-slip racing pedals