BC0149 – Mitsubishi 6G72/VR-4 Stroker Kit – 84mm Stroke/ProH2K Rods

In the pursuit of significant, reliable horsepower, engine displacement remains a foundational truth. For the Mitsubishi 6G72 platform, particularly the revered twin-turbo VR-4 variants, the path to ultimate torque and power density is paved with a meticulously engineered stroker assembly. The BC0149 Stroker Kit from Brian Crower isn’t merely an assortment of parts; it is a fully integrated, precision-machined system designed to transform the 3.0L 6G72 into a robust 3.4L powerhouse. Engineered for the rigors of forced induction and high-RPM operation, this kit leverages an 84mm stroke billet crankshaft, proprietary ProH2K connecting rods, and forged pistons to deliver an unparalleled combination of strength, responsiveness, and volumetric efficiency. It represents the definitive solution for builders who demand nothing less than absolute mechanical integrity and peak performance from their platform.

Engineering the Foundation: The 4340 Billet Crankshaft

The heart of any stroker kit is its crankshaft, and the BC0149 is centered around a masterpiece of metallurgy and machining. Fabricated from 4340 chromoly billet steel, this crank undergoes a rigorous process of CNC machining, heat-treating, and micro-polishing to achieve its final form. The critical increase to an 84mm stroke is executed with precision, maintaining optimal rod angularity and piston speed characteristics to ensure engine longevity and smooth operation. Each journal is micro-polished to a mirror finish, drastically reducing friction and wear on the main and rod bearings. Furthermore, the crankshaft is fully counterweighted and balanced to exacting standards, a non-negotiable requirement for a smooth-revving, high-performance engine that will see sustained high-RPM use. This component alone elevates the entire rotating assembly’s potential, providing a stable, unyielding foundation for immense cylinder pressure. For a deeper technical understanding of crankshaft metallurgy and design principles, consider this resource on performance crankshaft design from industry experts.

The ProH2K Connecting Rods: Redefining Tensile Strength

Connecting the increased stroke of the crank to the pistons are Brian Crower’s signature ProH2K connecting rods. These are not simply repurposed H-beam rods; they represent a specific, advanced alloy and manufacturing process. The “H2K” designation refers to a proprietary 4340+ material that is heat-treated to achieve an ultimate tensile strength exceeding 220,000 psi—a figure that places them in the upper echelon of performance connecting rods. This extraordinary strength-to-weight ratio is critical in a stroker application, where piston speed and inertial forces are increased. The ProH2K design features a stepped I-beam profile in the center for immense rigidity, coupled with a precision-machined H-beam style at the ends for optimal weight reduction and strength. Every rod is shot-peened, magnafluxed for cracks, and weight-matched to within 1 gram to ensure perfect harmonic balance within the rotating assembly, directly contributing to reduced bearing wear and enhanced engine stability.

Forged Pistons & Complete Rotating Assembly Balance

Completing the reciprocating assembly are custom forged aluminum pistons, designed specifically for this 84mm stroke application. These pistons account for the altered deck height and compression ratio requirements that come with a stroker crank. Typically manufactured from 2618 forgings, they offer superior ductility and fatigue resistance under extreme heat and pressure compared to hypereutectic cast pistons, making them mandatory for high-boost or nitrous applications. The pistons include valve reliefs machined to accommodate aggressive camshaft profiles and feature a durable anodized skirt coating to reduce friction. Crucially, the entire BC0149 kit—crankshaft, rods, pistons, and pins—is balanced as a complete unit. This “spin-balancing” process ensures that the inertial forces of the rotating and reciprocating masses are neutralized, resulting in dramatically reduced harmonics, lower bearing loads, and a smoother power delivery that extends the operational lifespan of every component in the long block.

• Substantial Displacement Increase: Elevates the 6G72 from 3.0L to a potent 3.4L, providing a foundational gain in torque and horsepower across the entire RPM band.
• Unmatched Rotating Assembly Strength: The synergy between the 4340 billet crank, ProH2K rods, and forged pistons creates a rotating assembly capable of supporting well over 800+ horsepower in boosted applications.
• Enhanced Engine Response and Volumetric Efficiency: The increased displacement improves cylinder filling (breathing), resulting in stronger low-end and mid-range torque, sharper throttle response, and a broader power curve.
• Engineered for Forced Induction: Every component is selected and manufactured with the high cylinder pressures of turbocharging or supercharging in mind, ensuring long-term reliability under stress.
• Precision-Balanced for High-RPM Stability: The fully balanced assembly minimizes destructive harmonics, allowing for safer, smoother operation at elevated RPM limits, which is critical for maximizing turbo efficiency.

Technical Specifications & Vehicle Fitment

The BC0149 Stroker Kit is a comprehensive solution designed for a direct, precision fit. Below are the critical technical specifications that define this performance package.

Vehicle Fitment & Application Notes

This stroker kit is engineered specifically for the Dual Overhead Cam (DOHC) version of the Mitsubishi 6G72 engine. Primary application is for the high-performance, twin-turbocharged variants found in the iconic chassis listed below. It is imperative to verify engine model and year before purchase. This kit is designed for performance/racing use and requires professional installation and tuning, including necessary supporting modifications (fuel system, engine management, turbo sizing, etc.) to realize its full potential and ensure reliability.

Primary Fitment:
• Mitsubishi 3000GT VR-4 (1991-1999)
• Mitsubishi GTO VR-4 (All Japanese Market DOHC 6G72 variants)
• Dodge Stealth R/T Turbo (1991-1993)
Note: This kit is intended for the DOHC 24-valve 6G72 engines. It is not compatible with the SOHC 12-valve versions. Always confirm your engine’s specific identification codes prior to ordering.