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2010 BMW Z4 35i and 2006 BMW Z4 M Coupe - Sibling Disobedience

Peter Wu
Nov 11, 2011

You can bet on an old-versus-new debate every time a new-gen model lands in the showrooms. You’ll have your supporters of the old talking about tradition and character or how the previous car had an analog feel instead of the new car’s digitized detachment. Supporters of the new model will talk about technology, microprocessors, advanced materials and the need to keep progressing or go the way of the Neanderthal.

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The two Z4s featured here could not be more different, so this isn’t so much a comparison as it is an example of how two siblings from the same branch of the family tree have gone on divergent evolutionary paths, with the newer car of the two still evolving.

Unlike some cars that start out as modest tuning projects and then snowball out of control, the owner of the first-gen E85 knew from the beginning he was going to build something specifically for the track. Having owned BMWs since the mid-’70s, including two M5s and an M6, the platform would either be based on a BMW or a Porsche. The car was built over the course of two winters by Fall-Line Motorsports in Buffalo Grove, Illinois, near Chicago. Fall-Line currently runs an M3 in the Grand-Am Koni Challenge series and build racecars for other people, so this E85 build was well within their window. Tim Stratton, the project’s point man, said the E85 chassis had similarities to both the E36 and E46 M3s he’s worked on.

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Fall-Line started by gutting the interior and welding in a six-point rollcage. The stock seats were swapped with carbon Cobra race seats and a Momo steering wheel sits on a quick-release hub. Just behind the wheel there’s an AiM Sports MXL dash/data acquisition logger.

For obvious reasons, with its massive flared fenders and exposed carbon weave, the exterior gets most of the attention. The lines of the kit are similar to but not exactly the same as a Flossmann body kit from Germany. Fall-Line commissioned Prototype Composites out of Glendale, Wisconsin, to fabricate a hood, roof and rear decklid and also create different mounting points for the Flossmann kit so they’d fit better. They also left the carbon/Kevlar-reinforced panels naked to show off the weave. A Crawford Designs Grand Am-spec rear wing is mounted via custom-made wind mounts also by Prototype Composites. As it sits now, Fall-Line managed to shave roughly 400 pounds off the stock car (2,850 vs. 3,240).

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The first thing you notice after you’ve climbed over the cage and into the Cobra seat is just how light the doors are. The panels can’t weigh more than a pound or two, and most of the weight of the doors comes from the metal frame. Aligning perfectly, the doors close with a secure click.

The engine fires up immediately and gets the interior vibrating to its rhythms. The characteristic metallic zing of a stock 3.2-liter straight six is replaced with a deeper rumble. It breathes through a CSL airbox and Dinan throttle bodies and cams. Spark, air and fuel are controlled by a Motec engine management system. And it exhales through a Supersprint stepped header and X-pipe, followed by a custom-built rear section utilizing Borla mufflers. A Fall-Line underdrive pulley kit helps the engine spin more freely. On a Mustang dyno, the engine made 351 whp at 8000 rpm and 255 lb-ft of wheel torque at 6600 rpm, and the rev limit was raised to 8300 rpm.

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The Sachs clutch is racecar stiff but it engages with enough progression to pull away cleanly. As it gathers speed, the gummy Yokohama slicks (280/650 front, 280/680 rear) pelt the underbody with pebbles and marbles, making it sound like the car’s being sprayed by a barrage of small-caliber rounds. Onto clean tarmac and the sound of gears being meshed and the lightly muffled exhaust takes over. It’s sensory overload, and these are just the warm-up laps.

We’re on the Autobahn Country Club’s South Track in Joliet, Illinois. In the passenger seat is Justin Fouts, from Fall-Line’s marketing department, who had earlier shown me the proper lines around the track’s mixture of 15 turns. After a tight first corner, the track unfurls into a series of left and right sweepers that increase in speed until a tricky, chicane-like turn 9-and-10 combo separates the layout’s two high-speed sectors.

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With some heat into the tires and brakes, I start to step more deeply into the throttle. There’s some slight hesitation when I first get into it, which may have been some bad gas, but the engine fought through it to send the meter on the digital dash shooting towards redline. Although torque is abundant, horsepower made through high revs is where the engine thrives. And because it’s utilizing Fall-Line’s shorter 4.10 differential, running through the gears happens just that much more quickly.

The car turns in sharply and the Yokohama slicks hang on tenaciously. The ride is racecar-stiff with the Moton Club Sports coilovers. The Brembo brakes (355mm slotted discs and four-piston calipers in front, 345mm slotted discs and four-piston calipers in back, Cobalt pads all around) wipe off speed with instant bite and seem to have plenty in reserve. Although I didn’t approach the limits in my few short laps, it was easy to tell that Fall-Line had dialed the car in beautifully. It responded to every input, be it brakes or steering, with direct, linear feedback. I’m sure there were some frightening levels of grip left on the table.

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Lapping the same track in the 3D Design Z4 couldn’t have been more different. Set up for the street and retaining all of its sound deadening materials, the car attacks the straights with a restrained whoosh of spooling turbos and the subtle snarl of the Eisenmann exhaust.

Midrange torque seemed to be the dominant characteristic, as with all N54 engines. This particular car’s ECU uses an ESS Tuning Stage 2 program that the company says is good for an extra 90 hp and 70 lb-ft of torque, for a total of 390 hp and 370 lb-ft. As it’s still a work in progress, the car is expecting a bigger, more-efficient intercooler.

Like other N54 engines, the little stock turbos start to run out of breath near the redline. Up to that point, the car surges through the gears effortlessly. There was enough power down low to get the back tires to slip coming out of the tighter turns before traction control spoiled the party. The power down the straights was impressive and it wouldn’t surprise me if we were hitting top speeds similar to its carbon-bodied E85 brother. But all that power made the brakes seem like the weakest link as they started to fade. More aggressive brake pads might be able to make up for that.

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The car sits on a rare set of M3 GTS wheels known as BBS Motorsports GT4 RE. They were brought in by 3D Design North America’s sister company, WheelSTO, and are wound with Yokohama Advan S-Drive tires. KW Variant 3 coilovers take care of the damping duties. 3D Design also had a company out of the Chicago area called IND Distribution take out the height adjustment collar to get the car to sit an extra half an inch lower in back. Dinan camber plates help tilt the front wheels in to clear the fenders and give it some extra turn-in.

The car eagerly attacked every corner it was thrown into and you could feel the front tires starting to slip before the rear started to rotate to get the balance back towards neutral. Then it was just a matter of feeding in the right amount of throttle. And even when the fading brakes meant that the corner had to be taken faster than desired, the car responded well to trailing brakes into the corner.

On the outside, the car wears 3D Design’s carbon M-Sport front lip, rear diffuser, side skirts and trunk spoiler. The result is subtle but adds a racier edge. Inside it’s fitted with 3D Design pedals and footrest and also their gauge pod. That pod and other parts of the dash panels, center console and roll bar covers were painted Alpine White by IND Distribution.

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Despite their diametric differences and reasons for being, both cars had that intangible BMW DNA at their core: driver-oriented, well-balanced and well-behaved. And, obviously, they’re great platforms to start with, whether for the track or the street.

2006 BMW Z4 M Coupe

Longitudinal front engine, rear-wheel drive

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3.2-liter I6, dohc, 24-valve. CSL airbox, Dinan cams and throttle bodies, Motec engine management, Supersprint header and X-pipe, custom exhaust, Borla muffler

Six-speed manual, Sachs clutch and flywheel, Fall-Line Motorsports 4.10 differential

Moton Club Sports adjustable coilovers

Brembo Gran Turismo assemblies, four-piston calipers, 355x32mm, two-piece, slotted discs, Cobalt XR1 pads (f), four-piston calipers, 345x28mm, two-piece, slotted discs, Cobalt XR3 pads (r)

Wheels and Tires
HRE Competition 90 Series, 11x18 (f), 11.5x18 (r)
Yokohama racing tires, 280/650 (f), 280/680 (r)

Carbon/Kevlar widebody fenders, rear quarter and front bumper modified from a Flossmann kit by Composite Prototypes. Roof, doors, rear decklid and hood carbon/Kevlar panels custom made by Composite Prototypes. Crawford Designs Grand-Am spec rear wing with Composite Prototype’s wind mounts

Cobra carbon racing seats, Momo quick-release steering wheel, six-point rollcage, AiM Sports MXL dash/data acquisition logger

Peak Power: 351 hp @ 8000 rpm
Peak Torque: 255 lb-ft @ 6600 rpm

*measured at wheels

2010 BMW Z4 35i

Longitudinal front engine, rear-wheel drive

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3.0-liter I6, dohc, 24-valve, twin-turbo. ESS Tuning Stage 2 ECU program, Eisenmann cat-back exhaust

Seven-speed DCT automated manual

KW Variant 3 coilovers, Dinan front camber plates

OEM calipers, 348mm vented rotors (f), 325mm vented rotors (r)

Wheels and Tires
BBS Motorsport BMW GT4 RE, 9.5x18 (f), 10x18 (r)
Yokohama Advan S-Drive, 235/40 (f), 255/35 (r)
BBS Motorsport lug nuts

3D Design body kit (front carbon-fiber splitter, carbon side skirts, carbon rear diffuser and trunk spoiler), tinted side markers and painted reflectors

3D Design three-gauge panel, 3D Design foot pedals, Stack 3500 Series gauges. Alpine White dash and interior panels

Peak Power: 390 hp
Peak Torque: 370 lb-ft

Autobahn Country Club

In the past few years, private racetracks have been popping up across the country. The idea is that you pay a one-time membership fee and then a yearly maintenance fee for the privilege of having access to the track or tracks practically any time you want. There are a few on the East Coast near the money and population density of New York and New Jersey and a few more scattered across the West and the South. In the Midwest, there’s the Autobahn Country Club in Joliet, Illinois, just an hour south of downtown Chicago.

The Autobahn Country Club was one of the first membership-style tracks in the U.S. and it either set the trend or shares a lot of similarities with the clubs of its ilk. First there’s the track, and, in this case, there are two courses, the North and South, which were designed by Alan Watson, a former director of the Brands Hatch Circuit in England and also the designer of road courses in Georgia, Arizona, Michigan and South Carolina. At Autobahn, the North and South courses can be connected to make one of the longest tracks in the States at 3.56 miles.

Like the other clubs, Autobahn offers driving courses for every skill level and they have a wide variety of performance cars to sample in their Autobahn Experience course, with a Caterham S300 looking particularly appealing.

Local race teams also use Autobahn’s tracks for testing and many of them have set up their own on-site garages for maintenance and storage, while some members have even built multi-storied homes along one of the faster stretches on the South track. And so nearly everyone can get involved; there’s also a karting track so Junior can hone his skills.

Being that members can get onto the track just about anytime they like from Tuesday to Sunday, it’s safe to assume that a lot of doctors, lawyers and CEOs are playing hooky or calling in sick during the racing season. And they’re taking a helmet and gloves instead of a bag of golf clubs to this country club.


Autobahn Country Club
Fall-Line Motorsports
3D Design
By Peter Wu
45 Articles



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