BC6708 – VW/Audi 1.8T – ProH625+ Connecting Rods w/ARP Custom Age 625+ Fasteners

Engineering the Foundation: Introducing the BC6708 ProH625+ Connecting Rod Set

For the dedicated builder of the Volkswagen Group’s venerable 1.8T engine, the connecting rod represents the critical pivot point between linear piston motion and rotational crankshaft force. It is the component that must withstand the brutal, repetitive shock loads of high-RPM operation and significant cylinder pressure. The BC6708 ProH625+ Connecting Rod Set from Brian Crower is not merely an upgrade; it is a fundamental re-engineering of this core component. Designed explicitly for the 20V 1.8T (EA113) platform, this set combines a proprietary, ultra-high-strength forged alloy with the industry’s most trusted fastening system. It is the definitive solution for builds targeting sustained performance beyond 500 horsepower, high-revving applications, or engines utilizing aggressive forced induction or nitrous oxide. This product transforms the engine’s lower end from a potential point of catastrophic failure into a bastion of predictable, reliable strength.

Material Science: The ProH625+ Forging Advantage

The “ProH625+” designation is not marketing jargon; it specifies a proprietary 4340 chromoly steel variant subjected to a precise multi-stage heat-treating process. This results in a material with a tensile strength exceeding 220,000 PSI and superior fatigue resistance compared to standard 4340 forgings. The forging process itself aligns the metal’s grain structure along the rod’s profile, creating a monolithic component free of the potential voids or inclusions found in cast or powdered metal rods. Each BC6708 rod is CNC-machined to exacting tolerances from this forged blank, ensuring perfect balance and weight consistency across the set. This precision minimizes destructive harmonic vibrations at elevated RPM, a critical factor for valve train stability and main bearing longevity. The rods feature a fracture-cap design at the big end, which, when assembled, creates a perfect, micron-level seal that is far stronger and more precise than a machined split. For an in-depth look at the metallurgy behind modern performance rods, consider this resource on connecting rod materials and processes.

The Fastener System: ARP Custom Age 625+ Bolts

A connecting rod is only as strong as its weakest point, which is invariably the fastener securing the rod cap. Brian Crower eliminates this variable by including ARP Custom Age 625+ fasteners as standard equipment. These are not generic bolts; they are aerospace-grade, directionally rolled thread fasteners made from a nickel-chromium super-alloy. The “Custom Age 625+” refers to ARP’s proprietary thermal aging process, which further enhances the fastener’s clamp load retention and resistance to stress relaxation under extreme heat and load. Compared to standard ARP 2000 or OEM torque-to-yield bolts, the 625+ alloy provides approximately 25% greater tensile strength, allowing for higher clamping force without compromising the fastener’s ductility. This ensures the rod cap remains absolutely fixed under the dynamic loads of high-RPM operation, preventing cap walk and the subsequent bearing failure it causes. Each fastener is pre-lubricated with ARP’s proprietary Ultra-Torque® lubricant, guaranteeing accurate and consistent clamp load during assembly when the specified torque-plus-angle procedure is followed.

Comprehensive Benefits of the BC6708 ProH625+ Rod Set

• Unmatched Tensile & Fatigue Strength: ProH625+ forged alloy withstands extreme cylinder pressures and inertial forces encountered in high-horsepower and high-RPM applications, providing a massive safety margin over stock components.
• Precision CNC Machining: Guarantees perfect bore alignment, center-to-center distance, and weight matching, which is critical for engine balance and smooth operation.
• Fracture-Cap Big End Design: Creates an exceptionally precise and strong big end bore for optimal bearing seating and oil clearance control, superior to a machined split.
• Industry-Leading Fastener Package: Includes genuine ARP 625+ bolts, offering the highest available clamp load and thermal stability, eliminating the rod bolts as a failure point.
• Optimized for Performance Use: Designed with the strength and durability required for sustained use with turbochargers, superchargers, and nitrous oxide systems where detonation or pre-ignition events are possible.
• Direct OEM Replacement Profile: Maintains stock rod length and piston pin diameter, ensuring compatibility with standard and aftermarket pistons without requiring custom crankshaft work.

Vehicle Fitment: Application-Specific Engineering

The BC6708 set is engineered as a direct, drop-in replacement for the factory connecting rods in the following Volkswagen AG vehicles equipped with the 1.8-liter 20V turbocharged (EA113) engine. It is crucial to verify your engine’s internal specifications (crank journal size, piston pin diameter) before purchase. This set is designed for the common 144mm center-to-center length and 19mm small end.

Volkswagen: Golf Mk4 (1999-2005), Jetta Mk4 (1999-2005), GTI 1.8T (1999-2005), Beetle 1.8T (1999-2005), Passat B5 (1998-2005).

Audi: A4 (B5, B6 chassis 1996-2005), TT (8N chassis 2000-2006), A6 (C5 chassis 1998-2004). Also applicable to many 1.8T longitudinal and transverse applications in this era.

Note: Always confirm engine code (e.g., AWP, AMB, AWW, etc.) and consult with your machine shop or builder. These rods are intended for performance rebuilt engines and require professional measurement, bearing selection, and assembly.

Technical Specifications & Dimensions

Disclaimer: All dimensions are nominal. Final machining and bearing selection for proper clearances must be performed by a qualified engine machinist based on measurements of your specific crankshaft journals and block.