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Precision Bearings Built for the 991 Turbo's High Boost Loads
The Porsche 991 Turbo's MA1.71 flat-six spins hard and loads its rod bearings with serious cylinder pressure from the factory twin-turbo setup. ACL's 6B2484H race series connecting rod bearing set replaces the stock bearings with a trimetal construction engineered to survive higher RPM, added boost, and repeated track sessions without the fade that stock bearings eventually show.
Key Features
- Trimetal construction (hardened steel back, copper-lead intermediate layer, tin overlay) for superior load capacity over stock bimetal bearings
- Reduced-friction surface finish that lowers operating temperatures and supports engine longevity under sustained boost
- Increased oil film retention for consistent lubrication during hard acceleration and extended high-RPM pulls
- Manufactured to tight tolerance bands for consistent, predictable clearances across the full 6B2484H set
- Purpose-built application for the 991 3.8L Turbo engine family, not a generic universal-fit bearing
- Trusted by engine builders for daily-driven and track-prepped 991 Turbo builds alike
Fitment Table
| Year Range | Make | Model | Trim |
|---|---|---|---|
| 2013-2016 | Porsche | 911 (991) | Turbo |
| 2013-2016 | Porsche | 911 (991) | Turbo S |
| 2013-2016 | Porsche | 911 (991) | Turbo Cabriolet |
| 2013-2016 | Porsche | 911 (991) | Turbo S Cabriolet |
Specifications
| Detail | Value |
|---|---|
| MPN | 6B2484H-STD |
| Brand | ACL |
| Bearing Type | Connecting Rod Bearing Set |
| Construction | Trimetal (steel back, copper-lead layer, tin overlay) |
| Clearance Size | Standard (STD) |
| Engine Code | MA1.71 3.8L Turbo H6 |
| Recommended Use | Street and track performance applications |
| UPC | Not published by manufacturer |
What's Included
- One complete set of ACL 6B2484H connecting rod bearing shells sized for all cylinders
- Manufacturer packaging with bearing size and clearance identification
About ACL
ACL Bearing Company has manufactured engine bearings in Australia for decades, supplying both OE replacement and race series bearings to builders worldwide. The ACL Race Series line uses trimetal construction specifically to handle the increased loads and temperatures found in forced-induction and high-RPM performance engines, making it a common choice for Porsche, European, and domestic performance rebuilds.
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FAQ
What is the 6B2484H-STD?The 6B2484H-STD is ACL's Race Series trimetal connecting rod bearing set built specifically for the Porsche 991 3.8L Turbo engine (MA1.71). It replaces the factory rod bearings with a construction designed for higher load and temperature tolerance.
Will this bearing set fit a non-turbo 991 Carrera?No. This bearing set is sized specifically for the MA1.71 3.8L Turbo engine and is not designed for the naturally aspirated 991 Carrera engines, which use different bearing dimensions.
What does STD clearance mean?STD indicates standard clearance, precision finished to match OEM crankshaft journal specifications. It is the correct choice for a stock or lightly refreshed crankshaft that has not been machined undersize.
Do I need to replace main bearings at the same time?It is not required, but many engine builders replace main and rod bearings together during a rebuild to ensure consistent wear characteristics and avoid a second teardown later.
Is this bearing set suitable for track use?Yes. The trimetal construction is specifically engineered for the higher loads and sustained temperatures seen in track driving and forced-induction applications, making it a common upgrade for track-prepped 991 Turbo builds.
What is trimetal bearing construction?Trimetal bearings use three layers, a hardened steel back for strength, a copper-lead intermediate layer for load capacity, and a thin tin overlay for break-in protection and corrosion resistance, offering more durability than a standard two-layer bimetal bearing.
Can I reuse my old bearings after inspection?Rod bearings are a wear item and should be replaced as a full set any time the rod caps are removed, since partial reuse can create uneven clearances and premature failure.
Does this bearing set come with installation instructions?Detailed clearance-checking and installation procedures are not included in the box and should follow a qualified engine builder's process, including plastigauge or micrometer clearance verification before final torque.
Install Instructions
- Remove the engine and disassemble to access the connecting rods and crankshaft per the factory service procedure.
- Inspect the crankshaft rod journals for wear, scoring, or out-of-round condition and machine if necessary before bearing installation.
- Clean all oil galleries and mating surfaces thoroughly before installing new bearing shells.
- Install the ACL 6B2484H-STD bearing shells into the rod and cap, ensuring correct orientation and full seating in the bearing bore.
- Verify oil clearance using plastigauge or a micrometer and bore gauge before final assembly.
- Torque connecting rod bolts to the manufacturer's specified value using the correct sequence and a calibrated torque wrench.
- Prime the oiling system before first startup to ensure immediate lubrication to the new bearings.
- Follow a proper break-in procedure and recheck for leaks or unusual noise after the first heat cycle.
Prop 65 Warning
WARNING: This product can expose you to chemicals including lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information, visit www.P65Warnings.ca.gov.
ACL
ACL manufactures performance engine bearings used in race engines across a wide range of motorsports disciplines, from sport compact and drift racing to oval track, drag racing, and land speed record applications. ACL Race Series bearings use a specialized tri-metal construction with a proprietary copper-lead alloy overlay that provides excellent load capacity, conformability, and wear resistance under the high RPM and cylinder pressure conditions of performance engines. Popular ACL Race Series Bearing Applications ACL Race Series bearings are available for main bearings, connecting rod bearings, and thrust washers across a broad range of American, Japanese, and European performance engines including Honda, Toyota, Subaru, Mitsubishi, Nissan, Ford, Chevrolet, and Dodge applications. ACL bearings are manufactured to OEM dimensional tolerances and are available in standard, 0.001-inch, 0.010-inch, and 0.020-inch undersize options to accommodate different crankshaft regrind specificati...
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