Article Summary
- Ronnie Fieg's Kith x BMW E53 packs a CarBahn-rebuilt S85 V10 and a six-speed manual conversion, while keeping the factory all-wheel-drive system.
- A bespoke 9,000 RPM instrument cluster was built from scratch, since the E53 never came with an engine that revved that high.
- The build was done in Lithuania under an OEM+ philosophy, meant to look and feel factory-correct despite the extensive custom engineering.
Ronnie Fieg’s latest project with BMW starts from a specific question: what if BMW M had built the original X5? The Kith BMW E53 takes the first-generation X5 and re-engineers it around one of the brand’s most well-regarded powertrains, following an OEM+ approach — heavy custom work, built to look and feel like it came from the factory this way.
“The idea was to build the ultimate E53 X5 that BMW never made,” Fieg told us exclusively. “We took a completely rebuilt CarBahn S85 V10 with forged pistons, converted the car to a six-speed manual and retained the factory all-wheel-drive system. Then we engineered everything around it — custom mounts, wiring, hardware, software, exhaust, suspension and brakes.”
The goal was to keep the E53’s identity intact while giving it a genuinely M-caliber heart. Instead of building a show car, the team leaned into subtlety: extensive fabrication and engineering hidden under a finish that reads as factory-correct down to the details. As Fieg put it, “Even though so much of the car is custom, the goal was for it to feel like something BMW could have built.”
Powertrain and Drivetrain
The build is centered on a 5.0-liter S85 V10 — the naturally aspirated engine from the E60-generation M5 — rebuilt by CarBahn with forged pistons. It’s paired with a six-speed manual, a gearbox the E53 never came with from the factory. Getting there took custom engine mounts, transmission mounts, wiring, hardware, and software to make the swap work with the car’s original architecture.
The team kept the E53’s factory all-wheel-drive system rather than converting to rear-wheel drive, integrating it with the S85 and manual gearbox to preserve the original platform’s character. A full custom exhaust was built specifically for the V10 swap.
Fieg said the hardest part of the build wasn’t the engine transplant itself. “Putting the V10 into the engine bay is one thing. Making the S85, six-speed manual, factory all-wheel-drive system, electronics, software, cluster and chassis all work together so the finished car feels factory is where the real engineering went.”
A Cluster Built From Scratch
The E53 was never offered with an engine that could rev anywhere near the S85’s redline, so the team built a new instrument cluster with a 9,000 RPM tachometer — a spec no factory E53 ever had. The cluster face was made using the same process BMW uses for its OEM parts, with custom software written to read the S85’s engine data correctly. They also had to work around the S85’s oil-level monitoring, which doesn’t use a dipstick, wiring its electronic readout into the new cluster.
Lots of Visual and Mechanical Upgrades
Suspension is a new sport setup built around KW components, tuned for the V10 swap. Braking comes from an upgraded M brake system with custom K-lettered calipers and sport rotors. The build sticks with BMW’s factory aerodynamic kit rather than an aftermarket body kit, keeping the E53’s original design language intact. Wheels are 20-inch BMW Style 87s — one of the E53’s more recognizable factory designs — fitted with spacers to get the stance right.
The cabin keeps its original E53 layout but gets a full leather dashboard, full leather door cards, custom Kith upholstery and detailing, and the new 9,000 RPM cluster in front of the driver.
The car was built in Lithuania, and the process touched nearly every system: fabrication, mechanical engineering, drivetrain integration, electrical work, software, and hand finishing.
Fieg is careful to draw a line between this car and a simple engine swap. The project is a full reengineering of the E53 around the S85 V10 and six-speed manual, with the factory all-wheel-drive system and period-correct BMW design carried through the whole build. The target, as he describes it, was the E53 M that BMW never made.
Speaking with BMWBLOG at the reveal of the E53 and the 2027 X5 (G65) at the BMW Villa in Pebble Beach, Fieg said the plan isn’t for this car to sit as a showpiece. He and his wife intend to make it their daily driver in New York.
