Garrett G-Series II G40-1250 CHRA Upgrade Unlocks 170 WHP on S58 BMW M3

When Boost Is No Longer the Answer

For high-horsepower BMW S58 builds, the limiting factor is no longer the engine. It is airflow. That was the case with this 2023 BMW M3 CS (G80) owned by Mike Angelo and built by Prayoonto Racing. The combination was already producing over 1000 horsepower, but the turbocharger had reached its limit.

Building a 1000 WHP Street S58

The goal from the start was clear. Build a street-capable S58 that could reliably produce 1000 horsepower. Prayoonto Racing developed a fully built engine and transmission package including upgraded pistons, rods, camshafts, and valvetrain components. The drivetrain was reinforced with a Dodson-upgraded 8HP-76 transmission, and the car runs on E85 fuel with twin Garrett GVW-40 wastegates for precise boost control.

The original turbocharger setup featured a Garrett G40-1150 G-Series turbocharger, which delivered 1023 horsepower and 847 lb-ft of torque. For most builds, that would mark the finish line. For this one, it became the starting point for the next phase.

The Limitation: Pressure Without Headroom

After initial street driving, the target shifted from 1000 WHP to 1200 WHP. The challenge was not tuning or supporting hardware. The limitation was airflow. The existing G40-1150 was already operating at 45 psi. According to Prayoonto Racing, pushing beyond that level on the S58 platform introduces the risk of head lift. Increasing boost further was not a viable or safe solution. This created a clear constraint. The combination needed more airflow, not more pressure.

The Solution: G-Series II CHRA Upgrade

Instead of redesigning the entire turbo system, the team upgraded the core of the turbocharger. The setup was converted from a G40-1150 G-Series configuration to a G40-1250 G-Series II using a CHRA swap. This approach delivered three critical advantages:

• Direct interchangeability with the existing turbine and compressor housings
• No fabrication or system redesign required
• Increased compressor flow capability at the same operating conditions

The G-Series II compressor aero supports up to 10 percent higher flow at peak pressure ratio and turbo speed compared to the previous generation. For a combination already at its boost limit, this provided the additional airflow required to move beyond the previous performance ceiling

.

The Results: 170 WHP Gain at the Same Boost

With no changes to the engine, fuel system, or boost level, the upgraded configuration produced 1192 horsepower and 1029 lb-ft of torque at 45 psi. This represents a gain of 170 wheel horsepower and 176 lb-ft of torque from a single component upgrade. The improvement was not limited to peak output. Power increased consistently beyond 4000 rpm, demonstrating the impact of improved compressor efficiency and airflow capacity across the usable powerband.

What This Means for S58 and High-Output Builds

This result highlights a key principle in high-performance turbo systems. When boost limits are reached, additional power must come from airflow and efficiency rather than increased pressure. The G-Series II upgrade path allows builders to unlock additional performance without reworking the entire turbo system. By maintaining the existing turbo architecture and upgrading the core, builders can reduce cost, complexity, and downtime while achieving meaningful performance gains.

G-Series II Turbocharger Lineup

The Garrett G-Series II lineup spans a wide range of frame sizes, providing a scalable upgrade path for performance builds:

G25-585 48mm
G25-700 54mm
G30-725 54mm
G30-825 58mm
G35-990 62mm
G40-1000 62mm
G40-1250 71mm
G42-1325 73mm
G42-1325C Compact 73mm
G42-1585 79mm
G45-1610 79mm