The Z4 M40i vs. A90 GR Supra

Why Toyota Replaced the JZ with BMW’s 3.0L Inline-Six

When Toyota’s fifth-generation Supra (A90 GR Supra) was announced, the internet exploded — not because it was returning, but because it would be powered by a BMW engine. At the heart of that controversy was the B58: a BMW-developed 3.0L turbocharged inline-six — the very same engine found in the BMW Z4 M40i, among other performance BMWs.

This wasn’t just Toyota outsourcing a powertrain; this was a tuning and engineering endorsement of the B58 engine as a worthy successor to one of the most revered engines of all time — the 2JZ-GTE. In this article, we’ll break down the B58’s role in modern performance cars, compare its performance in the Z4 M40i vs. A90 GR Supra, and explain why this engine has earned legendary status among modern tuners, engineers, and enthusiasts alike.

🧬 BMW’s B58: A Modular, Overbuilt Inline-Six

The B58 was introduced in 2015 as a replacement for the N55 and was designed with three key goals:

• Increased thermal efficiency

• Greater power scalability

• Compliance with stricter emissions standards

From a technical standpoint, the B58 introduced several features that positioned it as a durable, high-performance unit:

The closed-deck block, forged crank, and over-engineered cooling system made the B58 capable of handling serious power gains even before any internal upgrades. This is why Toyota — a company known for conservative, long-lasting performance — chose it as the heart of its modern halo car.

🚗 Z4 M40i vs. A90 GR Supra: Two Flavors of the Same Engine

Both the BMW Z4 M40i and the A90 Supra 3.0 use variants of the B58 TU1 (B58 Gen 2), but there are key differences in calibration, response, and application philosophy.

Key Insight: While both engines are mechanically similar, Toyota’s calibration is more aggressive in later years, offering quicker throttle mapping, more linear boost delivery, and a sharper sports car character. The Supra’s ECU tuning also differs slightly to accommodate Toyota's proprietary software stack, which makes tuning slightly different despite hardware parity.

🧰 Why the B58 Was Chosen Over the 2JZ Lineage

Toyota's 2JZ-GTE was legendary not because of its power output (280–320 hp), but because of its tuning headroom. Built with a cast iron block, forged internals, and an ultra-strong bottom end, it became the benchmark for what a turbocharged inline-six could achieve. Enthusiasts pushed it to 800–1,000+ hp with proper fueling and turbos.

So why replace that with a BMW engine?

Toyota’s Reasoning:

• Modern emissions regulations made the 2JZ obsolete from a compliance standpoint

• BMW's modular B58 already had a high-strength aluminum block and could meet emissions without compromising power

• The B58 was lightweight, efficient, and overbuilt, much like the original 2JZ

• Toyota engineers were heavily involved in chassis tuning, cooling system revisions, and final drivability — ensuring the Supra wouldn’t just feel like a rebadged Z4

In short: The B58 was the only engine on the market that could match the spirit of the 2JZ while surviving in a post-Euro 6 world.

🔧 Aftermarket Support & Tuning Potential

The B58's rise in tuning culture has been meteoric:

Tools Used:

• MHD, BM3 (Bootmod3), Ecutek

• Custom flex fuel setups

• Port injection controllers for additional fueling

• ZF8HP transmission tuning for better torque handling

Both the Z4 and Supra share these tuning pathways — but the Supra has a slight edge in community development, given its cult following and JDM audience overlap.

🔍 Comparative Summary: Supra vs Z4 (Engine & Performance)

Conclusion: Mechanically equal, the Supra feels more raw and ready, while the Z4 is more balanced and refined — but both benefit from the same B58 powerhouse and respond identically to tuning.

✅ Final Thoughts: The B58 Is the Bridge Between Eras

The BMW B58 engine represents more than just an evolution of inline-six technology — it's a benchmark for modern turbo performance. That Toyota — a company with its own iconic powertrain heritage — chose the B58 to power its flagship coupe is the ultimate seal of approval.

Whether in a Z4 M40i or a GR Supra, the B58 continues to prove its worth — delivering OEM refinement, tuning potential, and long-term durability in a single, modular package. Its status as the "modern 2JZ" isn't just fan service — it’s earned.

At RPM Performance, we work extensively with both B48 and B58 platforms, offering calibrated ECU tuning, hybrid turbo builds, bolt-on packages, and full custom solutions for Supra and BMW owners alike. 

Want to experience a whole new level of performance? Contact us now!