MTG Dynamics B58/S58 Billet Main Caps

When building a high-horsepower BMW B58 engine, the strength of the bottom end becomes just as important as the rotating assembly itself. As cylinder pressure, boost, and RPM increase, the factory cast main caps can begin to flex under extreme loads. Even minimal cap movement can affect main bearing alignment, bearing clearances, and crankshaft stability.

The MTG Dynamics B58/S58 Billet Main Caps are CNC-machined from premium billet steel to provide substantially greater rigidity than the factory main caps. Designed for serious engine builders, these caps help maintain precise main bore geometry, reduce cap walk, and provide the stable crankshaft support required for extreme horsepower applications.

Whether you're building a 900 HP street car or a 1,500+ HP drag or roll racing engine, billet main caps provide one of the strongest foundations for a reliable B58 engine.

Features

• CNC-machined from high-strength billet steel

• Direct replacement for factory B58/s58 main caps (professional machining required)

• Significantly stronger than OEM cast main caps

• Helps reduce main cap walk under extreme cylinder pressure

• Improves crankshaft stability at high RPM

• Maintains consistent main bearing geometry

• Promotes improved bearing life and oil clearance consistency

• Designed for high-boost and high-horsepower engine builds

• Manufactured in the Turkiye

Benefits

• Stronger bottom-end foundation

• Reduced main cap flex

• Improved bearing reliability

• Better crankshaft support

• Increased durability for extreme horsepower applications

• Ideal for race, drag, roll racing, and high-performance street builds

Installation Notes

Professional engine machining is required.

These billet main caps are not a bolt-on upgrade. Installation requires:

• Line boring

• Align honing

• Verification of main bearing housing bore dimensions

• Proper main bearing clearance measurement during engine assembly

Failure to perform these machining operations may result in premature bearing failure or engine damage.

Recommended Applications

• 800+ HP Street Builds

• Big Turbo B58 Builds

• Drag Racing

• Roll Racing

• Standing Mile Competition

• Road Racing

• Dedicated Competition Engines

Engine Fitment

Fits BMW B58 Gen 1 and Gen 2 engines, including:

• BMW M140i

• BMW M240i

• BMW 340i

• BMW 440i

• BMW 540i

• BMW 640i GT

• BMW 740i

• BMW X3 M40i

• BMW X4 M40i

• BMW X5 xDrive40i

• BMW X6 xDrive40i

• BMW X7 xDrive40i

• BMW Z4 M40i

• Toyota GR Supra (A90/A91)