• The Pit+Paddock x Bilstein E91 M3 GTS is full steam ahead as Precision Sport Industries (PSI) starts installing aftermarket upgrades onto the freshly painted Fire Orange wagon.
• StopTech’s 380mm Trophy kit for the E9X M3 is designed to offer the very best braking performance for track-day enthusiasts, pro-am drivers, or street enthusiasts who demand more from their equipment.
• SPL is renowned for producing high-quality components for top race teams and its reputation has created a fervent desire for its products amongst discerning BMW enthusiasts.
• Additional upgrades include a full refurbishment of OEM parts, OEM M3 sway bars, Powerflex bushings, a new differential with MOTUL 75w140 fluid, a custom wiring harness, and more.

If there’s a lesson that you should extract from our Pit+Paddock E91 GTS Tribute project so far, is this: creating the very best means there’s often much more than meets the eye. The Transformers theme song is looping in my head now as I recall all of the tedious work that our build partner, Precision Sports Industries (PSI) has performed under the skin, but transformative is exactly what this build is becoming.

This round of mods marks an important midpoint of the project. It seems like ages ago that two cars — an E90 M3 and an unassuming, rear-wheel-drive E91 328i — arrived at PSI a few months ago. With their powers combined, the two cars will create the E91 M3 that never existed. But as you can already tell, our total effort benchmarks something much more ambitious than that: a fully modded, 4.6-liter powered M3 wagon conversion that would rival the range-topping E92 GTS. With the car freshly returned from its Fire Orange respray — an important GTS carryover trait — upgrades are coming in fast and this latest chapter picks up where we left off: suspension.

BEST SUPPORTING CAST

Pairing an impressively capable set of Bilstein 2-way Clubsport with factory suspension arms and rubber bushings would be a disservice to our goals. To ensure our chassis could extract the most from the Clubsport’s loftier threshold, we opted to fit the entire SPL suspension catalog on the wagon. SPL is renowned for producing high-quality components for top race programs in various series. Its reputation for achievement and reliability has created a fervent desire for its products amongst discerning BMW enthusiasts. Throughout this suite, spherical rod ends are used instead of rubber. The change provides a much more direct, confident response and grip — especially during corner entry and exit — where OEM rubber would otherwise be unsettling.

The upgrade warranted a complete refresh or new, factory replacement of its surrounding components. Fresh OEM trailing arms, camber arms, E9X M3 sway bars, uprights, and hubs were sourced to ensure there would be no weak links.

The subframe was treated to a fresh powder coat and a helping of fresh bushings from Powerflex, too. It’s been a go-to brand for BMW owners who want more out of their cars over the last three decades. Its yellow (70A) and purple (80A) polyurethane bushings will improve the wagon’s chassis response without giving away too much in terms of comfort and NVH. 

FULL STOP

The additional grunt from the 4.6-liter Carbahn stroker motor required a robust brake solution. StopTech’s 380mm Trophy kit for the E9X M3 is designed to offer the very best braking performance for track-day enthusiasts, pro-am drivers, or street enthusiasts who demand more from their equipment. The Trophy’s unique 6-piston caliper shape provides the appropriate clearance for 18” diameter wheels, which we plan to run to maintain that track-focused aesthetic.

More than the shape, the Trophy caliper also comes in a unique nickel-plated finish, which immediately sets it apart from other big brake kit options. These calipers are 20% lighter, thanks to extra machining work, and the rotors boast a 50% increase in available airflow. The net effect of all this effort is an immense increase in brake performance and heat management.

BIG DIFFERENCE

In the spirit of eliminating any weak links, a fresh 3.15 DCT differential from Diffs Online was sourced as well. Although we could’ve used this as an opportunity to throw in a different final gear, the uprated torque from the new engine should provide enough grunt to offset the difference without creating “buzzy” cruising speeds. Striking the right balance is key. For a project of this caliber, MOTUL’s 75w140 gear oil was the only logical choice. The combination of its lubricating power and ability to withstand motorsport-grade temperatures provides industry-leading anti-wear characteristics, oil film resistance, and reduces drivetrain noise.

THROUGH THE WIRE

As we stated in our first episode, having two cars provides a strategic advantage in creating the best possible end product. Between the E90 M3 and the E91 328i, there were two complete wiring harnesses available. To make a harness for our E91 M3, the Precision Sport Industries team had to identify each car’s unique factory option set. From there, they had to assess which leads needed to be retained and perform every un-pin and re-pin procedure where necessary. The length of this paragraph isn’t a proper acknowledgment of the effort involved, and it’s another testament to PSI’s incredible proficiency in helping us realize our ultimate vision.

NOT DONE YET

Before we go topside, there are a few more mods we plan to address underneath the car in the next chapter of the Pit+Paddock x Bilstein E91 GTS Tribute build. I can’t wait to show you what’s next, but stopping to admire everything we’ve done so far is important because the project is no small undertaking. Be sure to subscribe to our YouTube channel to keep up with our progress and see you next time.

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