ACL Releases New BMW Performance Bearing Application Guide
A Deep Dive Into ACL’s BMW Engine Bearing Range
ACL has officially released its latest BMW Application Guide for ACL RACE Series performance engine bearings (document code BMWAG26). For anyone building, refreshing, or upgrading a BMW engine—whether it’s a classic naturally aspirated inline-six, a high-revving M engine, or a modern turbocharged powerhouse—this guide is a valuable technical reference.
At Spool Imports, we supply a significant volume of ACL BMW bearings, so this post breaks down what the new guide covers, which BMW engines are supported, and how to use ACL’s sizing options to match your build goals.
Why This BMW Guide Matters
BMW engines are known for precision engineering and tight tolerances. Once power, RPM, or sustained track use increases, correct bearing selection and oil clearance control become critical.
The ACL BMW Application Guide consolidates key information including:
- Engine-specific conrod and main bearing listings
- Availability of standard, oversize, HX (extra clearance), and selected coated options
- Coverage spanning classic BMW engines through to modern turbo platforms
- Practical guidance on oil clearance optimisation and bearing mixing
ACL RACE Series – Designed for Performance BMW Engines
ACL RACE Series bearings carry strong motorsport pedigree and are engineered for durability under elevated cylinder pressure and sustained high load. The RACE Series construction used in these BMW listings includes a high-strength steel backing with performance-oriented lining and overlay design.
For performance BMW engines—especially turbocharged and high-RPM builds—bearing stability, fatigue strength, heat transfer, and seizure resistance are all essential. This is exactly the operating envelope ACL targets with the RACE Series range.
BMW Engine Families Supported by ACL (Highlights)
One of the strongest aspects of the new guide is the breadth of coverage. ACL has not focused only on modern engines—this is a wide BMW spread that includes mainstream platforms, M engines, and select MINI engines (BMW-era).
Modern Turbocharged BMW Engines
These are some of the most commonly rebuilt and upgraded BMW engines today:
- N54B30 – Twin turbo inline-6
- N55B30 – Turbo inline-6
- S55B30 – M twin turbo inline-6
- B58B30 – Modern turbo inline-6
- S58B30 – Latest M twin turbo inline-6
ACL offers both conrod and main bearings for these families in RACE Series form, with HX options available for builders targeting additional oil clearance.
Naturally Aspirated Inline-6 Engines
- M20 family (B20, B23, B25, B27)
- M50 / M52 / M54 families
- N52 / N53 families
These engines remain extremely popular for rebuilds, restorations, and swaps. ACL’s sizing range and RACE Series material design are well suited to engines that see higher RPM, spirited use, or track work.
BMW M Engines
- S14 (classic E30 M3 family)
- S50 / S52 (early M inline-6 families)
- S54 (E46 M3)
- S62 (E39 M5 V8)
- S65 (E9X M3 V8)
- S85 (E60 M5 V10)
- S63 / N63 (twin-turbo V8 families)
These engines place serious demands on bearing material and stability, particularly with increased RPM, tuning, or track duty. The new guide makes it much easier to confirm the correct ACL RACE Series set for your specific BMW engine code.
Oil Clearance Control: Understanding ACL “HX” (Extra Clearance)
A key feature of the ACL RACE Series BMW range is the availability of HX bearings, which are designed to provide additional oil clearance compared to standard sizing. This gives builders another lever to pull when dialling in a performance engine.
The guide also outlines a common engine-building method: mixing adjacent bearing grades to fine-tune clearance. This is especially useful when matching real-world crank measurements, block tunnel conditions, and the intended operating environment (street, track, high-boost, etc.).
Why Spool Imports Recommends ACL for BMW Builds
We continue to supply ACL bearings for BMW engines because they consistently deliver:
- Proven performance in demanding street and motorsport applications
- Broad coverage across BMW engine families (including many M engines)
- Multiple sizing options to match real-world machining and build goals
- Strong documentation support—now improved further with this BMW-specific guide
If you’re building a BMW engine and want help matching the right ACL conrod and main bearings to your crank measurements and target clearances, contact Spool Imports with your engine code and build intent (street/track/power level).
Download the ACL RACE Series BMW Application Guide (BMWAG26): Click here to view the PDF .
FAQs
What is the ACL BMW Application Guide?
It’s a BMW-specific reference document (BMWAG26) that lists ACL RACE Series conrod and main bearing sets for a wide range of BMW engines, along with sizing options such as standard and extra-clearance variants.
Which BMW engines does ACL support with RACE Series bearings?
The guide includes coverage across multiple BMW families, including popular turbo engines (N54, N55, S55, B58, S58), naturally aspirated inline-6 platforms (M20, M50/M52/M54, N52/N53), and a strong spread of M engines (S14, S54, S62, S65, S85), plus twin-turbo V8 families (S63/N63).
What does “HX” mean on ACL bearing part numbers?
HX indicates an extra-clearance bearing option. Builders typically use HX variants when they want additional oil clearance for performance use cases such as sustained high RPM, high load, or turbocharged applications.
Can I mix bearing shells to fine-tune oil clearance?
Yes. The guide outlines common practice of mixing adjacent bearing grades to achieve a target oil clearance. This should always be done based on accurate measurements of your crank journals and housing bores, and with appropriate engine-building process and verification.
Do I need conrod bearings, main bearings, or both?
Most full rebuilds and performance builds replace both. Conrod bearings support the rod big-end journals, while main bearings support the crankshaft in the block. The right choice depends on your engine, build scope, and inspection results.
How do I make sure I order the correct ACL BMW bearing set?
Confirm your exact BMW engine code, then measure your crank journals and housing bores. From there, select the ACL set and sizing (standard, oversize, or HX) that matches your measurements and target oil clearance. If you want assistance, Spool Imports can help you match the correct set to your build.
Need Help Choosing the Right BMW ACL Bearings?
Bearing selection is not one-size-fits-all. Intended use, power level, oil viscosity, crank condition, machining tolerances, and target oil clearance all matter. If you want a second set of eyes on your bearing choice, contact Spool Imports with your engine code and measurements.
