Project BMW Z4 >M

The modifications in this series will be specifically compatible to both the new Z4 M Coupe and M Roadster models. Some upgrades may also work for the non-M Z4 models. There are specific performance objectives and the whole process will be governed by the following guidelines:

Avoid (where possible) warranty-voiding issues to keep the highly useful and paid-for warranty intact.

Adopt a minimalist philosophy. Parts can be replaced, but additional systems will not be added.

Use the scientific method to test and report the merits of all performance enhancements. Control, or baseline, measurements will be compared to the new enhancements in a progressive manner.

No irreversible modification, so it may be returned to stock prior to its eventual sale (in about three years' time).

Real-world testing with a repeatable method of data collection is essential in any quantitative scientific analysis. In this case, it'll be fun too, using the acclaimed Traqmate GPS data acquisition system for lap times, acceleration, braking and lateral g measurements. Later, a two-wheel dyno will measure the relative improvement of each power upgrade.

The Traqmate Complete system was purchased online from Apex Performance, a race supply outfitter located near Pittsburgh, Pennsylvania. This data acquisition system is a cinch to install and use, and better still, it can store a whole track day's worth (and then some) of data. Analysis can be carried out trackside with a laptop, or later at home on a desktop PC with the included Traqview software.

I know the M pretty well now, with seat time both on the street and at a few track outings. Although the suspension is firm and the cornering exceptionally flat, the car can be a little unsure at turn-in. Unlike the E46 M3, the M Coupe does not include a front upper strut brace as standard. A quick look at the BMW accessory listing reveals an OEM front strut brace for the non-M Z4 (part # 51 71 0 305 114). Would it fit over the M's larger S54 engine? It took all of 15 minutes to find out. Simply remove the three nuts on top of the strut tower (be careful not to bump the car and disturb the camber setting), then, with the supplied hardware, bolt up the strut brace mount and torque to 25 ft-lb. Do the same for the other side, and then the bar can be bolted in place securely. Pretty easy, and yes, it clears the Z4 M's engine as it could (and should) have.

Is there a difference? After some spirited runs through the mountains, it's clear the front end is noticeably tighter and better connected to the road, the uncertain turn-in is reduced significantly. To quantify this, I grabbed the Traqmate system and drove to my home track, the two-mile, 11-turn road course at Race City Motorsport Park in Calgary, Alberta. Lap sessions were measured both with and without the strut brace assembly in place. Measurements were performed on the same day, with the same driver, with no in-car lap times displayed to provide motivation. The results revealed the average lap time-in stock form-was 100.8 seconds. With the strut brace, times dropped to an average of 98 seconds, the fastest time being 96.7. The table shows the displays generated by Traqview: the track map and the fastest laps with distance plotted, with respect to each of lateral gs, longitudinal gs and velocity. Baseline results are plotted in blue; in red with the strut bar installed. The red lines indicate more confidence coming into high-speed corners (turns 1 and 9) and that more velocity and lateral g-forces could be sustained through most corners. The front strut brace truly does a great job to keep the front contact patches more stable through the corners.

The next points to address were wheel and tire upgrades. When such upgrades are done just for looks, it can be dangerous, as this can adversely affect handling. The goal here was to enhance handling by taking a different approach: not wanting to increase the 18-inch wheel diameter or weight, yet increasing the contact patch and using stickier rubber.

Forgeline Motorsports has a great reputation for building durable and lightweight forged wheels. The company's newest competition wheel, ZX3-R, uses true-forged 6061 T6 aluminum centers and 6061 T6 spun rim halves for optimum strength and weight savings. It also helps that the ZX3-R is gorgeous. Each is custom-made to fit customer requirements and vehicle specification. I ordered a staggered set of 9x18 (offset: +39mm) and 10x18 (offset: +30mm), each wheel weighing 19 and 20 pounds, respectively. This is a significant weight saving over the stock wheels, which have an inch less width at the front and rear.

Nitto provided a set of its well-respected Invo ultra high performance summer tires, sized 245/40 front and 275/35 for the rear (compared to the 225/45 and 255/40 OE tires). The Invo's tread pattern is sharp and aggressive, with a high-surface-area outer section, and a high-tech silica-reinforced rubber compound to reduce tread flex and contribute to increased performance and a longer life. On the street, they give a quiet, comfortable ride with outstanding dry grip.

The new wheel/tire combination weighs 48.5 pounds in front (a two-pound saving), and 51 pounds at the rear (a four-pound saving). This may seem insignificant-only a 12-pound saving overall-but this includes tire upsizing. Reducing unsprung weight is advantageous when it comes to handling, especially so when it affects rotational momentum. At the track, the new set-up improved handling and grip, resulting in laps times almost three seconds less than with the OEM wheels and tires. The average time was 95.1 seconds, the fastest lap being 93.9. Referring to the table, the black line represents a hot lap with the wheel/tire upgrade. Faster exit speeds result in higher speeds on the straights, and more confident braking at the end of the straights, all due to the larger contact patch, the Invo technology and lighter wheels. Note that lateral g and corner speeds are up all round, especially at the notoriously slippery chicane (turns 8A and 8B). The Nittos are excellent track performers, both cold and hot, even with their relatively high 260 tire wear rating.

Confidence-inspiring upgrades are the ones that really count toward improving overall vehicle performance on the street and at the track. This trend will be continued by addressing the brakes in the next installment, followed by the addition of a coilover suspension.