B58 S58 Billet Main Caps
We Found the Limit. We Built the Solution!
At 5150 AutoSport, we don’t develop parts because they are trendy. Every part we make has a purpose!
When building a high-performance engine, most conversations focus on turbochargers, pistons, rods, camshafts, and especially dyno results. But behind every reliable high-horsepower engine is a foundation capable of handling extreme loads.
For engines making 1,200+ horsepower, every component matters.
We Don’t Make Parts Just To Be Cool
The main caps are one of the most critical parts of the engine’s foundation. Their job is simple but extremely important: securely support the crankshaft while maintaining precise main bearing alignment under extreme cylinder pressure, RPM, and torque loads.
At factory power levels, B48, B58, and S58 designs perform exceptionally well. But once these engines are pushed beyond their original limits, the forces inside the engine change dramatically.
More boost. More cylinder pressure. Higher RPM. More torque.
That is where the development of the 5150 AutoSport Billet Main Caps for the B48, B58, and S58 platforms began.
Our products are developed through real engine builds, race programs, customer feedback, and working directly with enthusiasts pushing BMW platforms to their limits.
As B48, B58, and S58 engines continued making more power, we started seeing the need for additional support in the main bearing structure.
Real Feedback. Real Testing. Real Solutions.
We don’t just sell a product and disappear. We stay involved with our customers and drivers, follow up on builds, and collect feedback from engines being pushed in real-world conditions.
Through this process, we began seeing concerns in high-power B58 and S58 applications, including:
- Main stud loosening after repeated high-load use
- Abnormal main bearing wear
- Changes in bearing clearances
- Increased bottom-end stress
- In some cases, main bearing failures
After inspecting engines in person, we identified signs of main cap distortion and abnormal bearing wear patterns.
This pointed to one critical area: main cap movement, also known as cap walk.
Why Cap Walk Matters
Cap walk occurs when the main caps move under extreme loads instead of maintaining proper alignment with the engine block.
Even small movement in a precision engine can create major problems, including:
- Reduced bearing life
- Loss of proper oil clearance
- Reduced oil pressure
- Crankshaft instability
- Main bore distortion
- Complete bottom-end failure
High boost, high RPM, aggressive tuning, and extreme cylinder pressure all increase the stress placed on the main bearing structure.
The Complete Solution
Fixing this issue requires more than just one component.
A strong bottom end starts with proper clamping force, stability, and bearing control.
The 5150 AutoSport solution includes:
5150 AutoSport Billet Main Caps
- CNC machined from high-strength billet material
- Heat-treated for increased durability
- Increased rigidity compared to factory cast components
- Precision dowel-pinned alignment
- Improved resistance against cap movement under extreme loads
ARP Main Studs
- Increased clamping force compared to factory fasteners
- Improved consistency under high-load conditions
- Helps keep the main structure securely located
5150 AutoSport Race Design Coated Main Bearings
- Designed to improve durability under extreme conditions
- Provides additional protection against heat, friction, and high-load operation
- Developed as part of a complete bottom-end solution
The dowel-pin design mechanically locates the main caps, helping prevent unwanted movement during extreme operating conditions.
After proper installation, line boring, and line honing, the result is a stronger foundation designed to maintain crankshaft stability and consistent bearing alignment.
We build parts because racers, engine builders, and enthusiasts need them.
5150 AutoSport
Built For Extreme BMW Performance.