BC6104 – Brian Crower ProH625+ Connecting Rods for Mitsubishi 4G63 (1st Gen/6-Bolt) with ARP Custom Age Fasteners

In the pantheon of legendary four-cylinder engines, the Mitsubishi 4G63 stands as a colossus. Its inherent strength and tunability forged its reputation in the fires of World Rally Championship dominance and grassroots drag strip warfare. To extract the next echelon of power and reliability from the 1st Generation, 6-bolt 4G63, the foundational rotating assembly must be addressed with components engineered without compromise. The BC6104 ProH625+ Connecting Rod Set from Brian Crower represents this exacting standard. Far more than merely upgraded factory components, these are purpose-built, race-proven rods designed to serve as the unyielding backbone for high-horsepower, high-RPM builds, transforming your engine’s lower end from a potential liability into an absolute asset.

Engineering the Unbreakable Link: ProH625+ Material & Design

At the core of the BC6104’s performance is its construction from ProH625+ premium alloy steel. This is not a standard 4340 material; it is a proprietary formulation and heat-treatment process developed by Brian Crower to achieve a superior balance of ultimate tensile strength and fatigue life. ProH625+ exhibits a nominal tensile strength of 180,000 PSI, a significant margin over conventional 4340 steel rods. This material science translates directly to mechanical confidence, allowing these rods to withstand the immense cylinder pressures generated by large turbochargers, aggressive nitrous oxide shots, and high levels of boost without fear of stretch, bend, or catastrophic failure.

The design philosophy extends beyond mere material selection. Each rod is machined from a premium-grade American steel forging, ensuring a continuous grain flow that follows the rod’s contours for optimal strength. Critical areas like the big-end beam and small-end pin bore are meticulously engineered with radii that eliminate stress risers—common failure points in lesser rods. Furthermore, the beams are shot-peened, a process that bombards the surface with small media to induce compressive stresses, dramatically improving resistance to fatigue cracks that can initiate under cyclic loading. This combination of advanced material and deliberate design creates a connecting rod that is, for all intents and purposes, unbreakable within the realistic operating window of a 4G63 platform.

Precision Machining for Flawless Integration & Balance

Raw strength is meaningless without precision. Every BC6104 rod undergoes CNC machining to exacting tolerances, ensuring consistency in length, center-to-center dimensions, and overall weight. This precision is paramount for maintaining proper piston deck height, optimizing quench, and achieving exemplary engine balance. A balanced rotating assembly reduces harmful harmonics, minimizes bearing wear, and allows the engine to rev more freely and reliably. The small-end pin bore is honed to a precise finish for optimal wrist pin fit and oil retention, while the big-end is sized to exact specification, ready for installation with performance rod bearings. This level of out-of-the-box precision saves hours of machining and balancing labor, providing a true “bolt-in” solution for builders seeking perfection.

Unmatched Fastener Technology: Included ARP Custom Age 2000® Fasteners

A connecting rod is only as strong as its weakest link, which is invariably the fastener. Brian Crower eliminates this concern by including the industry gold standard: ARP Custom Age 2000® rod bolts as part of the BC6104 kit. These are not generic ARP bolts; they are custom-spec fasteners designed specifically for this rod application. Manufactured from a proprietary 8740 chrome molybdenum steel alloy and subjected to ARP’s renowned “Custom Age” heat treatment process, these fasteners achieve an unparalleled clamp load with reduced stress risk.

The advantage of this partnership is profound. The ARP fasteners provide a more consistent, reliable, and reusable clamping force compared to any OE-style or lesser aftermarket bolt. Their fatigue resistance is exceptional, which is critical in a high-performance engine where rods are constantly subjected to tension and compression cycles. Using a torque-to-yield method with the included ARP Ultra-Torque® lubricant ensures perfect preload every time, securing the rod cap with absolute authority and eliminating cap walk—a primary cause of bearing failure. This inclusion makes the BC6104 a complete, no-compromise package.

Comprehensive Benefits & Vehicle Fitment

The BC6104 ProH625+ Rods deliver a system-wide upgrade to your 4G63’s durability and performance envelope. Below are the key benefits this set provides:

• Extreme Strength & Durability: ProH625+ alloy with 180,000 PSI tensile strength handles 1000+ horsepower applications with a significant safety margin.
• Race-Proven Reliability: Shot-peened beams and stress-relieved design combat metal fatigue for extended service life under extreme conditions.
• Precision Balanced & Machined: CNC-machined to ultra-close tolerances for perfect fitment, optimal balance, and reduced assembly time.
• Complete Fastener Solution: Includes custom ARP 2000® rod bolts and nuts, ensuring maximum clamp load and fastener integrity.
• Direct OE Replacement: Designed as a direct-fit for the 6-bolt 4G63, requiring no block machining or unusual bearing sizes.
• Foundation for High RPM: Robust design stabilizes the rotating assembly, enabling safer, sustained high-RPM operation.

Vehicle Fitment: 1st Generation (6-Bolt) Mitsubishi 4G63 Engines

The BC6104 set is engineered specifically for the early-style, 6-bolt crankshaft 4G63 engine. This fitment is critical, as the 2nd Generation (7-bolt) engines use a different rod design. These rods are a direct replacement for the factory components in the following applications:

• Mitsubishi Eclipse GS-T / GSX: 1990-1992.5 (6-bolt engines)
• Mitsubishi Galant VR-4: 1991-1992
• Eagle Talon TSi AWD / FWD: 1990-1992.5 (6-bolt engines)
• Plymouth Laser RS Turbo AWD / FWD: 1990-1992
• Various Import & JDM Applications: Including early Lancer Evolution I-III (where equipped with 6-bolt block) and other vehicles utilizing the 6-bolt 4G63 powerplant.

Note: Always verify your engine’s crankshaft bolt pattern (6-bolt vs. 7-bolt) before purchasing. The 6-bolt pattern features six bolts securing the flywheel/flexplate to the crankshaft flange.

Technical Specifications & Conclusion

The following table details the precise technical specifications of the BC6104 Connecting Rod Set. These figures are vital for engine builders calculating compression height, selecting pistons, and planning the complete rotating assembly.

For builders dedicated to pushing the 4G63 platform to its absolute limits, the Brian Crower BC6104 ProH625+ Connecting Rod set is not an option—it is a fundamental requirement. It synthesizes cutting-edge material science, precision manufacturing, and top-tier fastener technology into a single, cohesive package. By choosing these rods, you are investing in the structural integrity of your engine, buying peace of mind at 8000 RPM, and laying the groundwork for a powertrain that is as reliable as it is powerful. This is the definitive connecting rod solution for the discerning 6-bolt 4G63 builder seeking maximum performance without sacrifice. To further understand the critical role of fastener technology in engine assembly, we recommend this technical article on fastener preload and clamping force from ARP.