AR8713 – Mitsubishi 6G72 ARP Main Studs

In the ruthless arena of performance engine building, where horsepower is king and reliability is the kingdom, the foundation upon which power is built is non-negotiable. For enthusiasts and professional builders of the venerable Mitsubishi 6G72 engine—found in legends like the 3000GT VR-4, Stealth R/T TT, and modernized in later applications—the factory main bearing cap fasteners represent a critical point of failure under elevated cylinder pressures and rotational forces. The ARP 207-5801, also known by its Brian Crower reference AR8713, is not merely an upgrade; it is a fundamental re-engineering of the engine’s backbone. These ARP Main Studs are manufactured to aerospace-grade specifications, transforming the clamping force and alignment integrity of the 6G72’s lower end. By replacing stretch-to-yield factory torque-to-yield bolts with precision-rolled, heat-treated 8740 chrome molybdenum steel studs, this kit provides an immutable foundation, ensuring main bearing bore stability, optimal oil clearance retention, and the absolute security required for forced induction, high-RPM, and high-displacement builds. This is the definitive solution for anyone serious about extracting maximum durability from the 6G72 platform.

The Core Principle: Why Studs Trump Bolts for the 6G72

The factory main bearing caps are secured with torque-to-yield (TTY) bolts. This design, while cost-effective for mass production, is a one-time-use component that stretches permanently during installation to achieve clamp load. Under the intense stress of performance operation, these bolts can relax, yield further, or even fracture, leading to catastrophic main bearing walk or bore distortion. The ARP 8713 kit utilizes a stud-and-nut system. Studs are threaded into the block and remain stationary; the main bearing cap is then lowered onto them and secured with a torqued nut. This method provides a perfectly perpendicular clamping force, eliminating the side-load and thread galling inherent in bolt installation. The result is a significantly more uniform and repeatable clamp load across all five main caps, a critical factor in maintaining perfect crankshaft alignment and bearing oil film integrity under extreme loads. For an in-depth look at fastener engineering principles, consider this resource on the science of stud versus bolt loading from ARP’s technical library.

Technical Advantages and Material Science

ARP’s proprietary manufacturing process sets the 6G72 main studs apart. Each stud begins as 8740 chromoly steel, chosen for its superb strength-to-weight ratio and fatigue resistance. The threads are cold-rolled after heat treatment, a process that compresses the grain structure along the thread root—the most common point of stress failure—rather than cutting it away. This creates a smoother, stronger thread with superior resistance to fatigue cracking. The studs are then heat-treated to a precise Rockwell C hardness and finished with ARP’s patented “Unbrako” 12-point nuts and ultra-flat, case-hardened washers. This complete system ensures that the applied torque translates directly into clamping force without loss to friction, providing a clamping load that far exceeds the yield point of the OEM fasteners.

• Unmatched Clamping Force: Provides a consistent, significantly higher clamp load than OEM TTY bolts, preventing main cap movement and bearing fretting.
• Precision Crankshaft Alignment: Maintains perfect main bore alignment, ensuring consistent bearing clearance and optimal oil pressure.
• Repeatable Installation: Unlike one-time-use bolts, ARP studs can be installed, torqued, removed, and re-torqued repeatedly without any loss of integrity.
• Enhanced Fatigue Life: Cold-rolled threads and premium material offer dramatically increased resistance to cyclic loading failures.
• Foundation for Forced Induction & High RPM: Essential for containing the increased cylinder pressures from turbocharging, supercharging, or sustained high-revving operation.
• Improved Oil Control: Stable main bore geometry helps maintain proper rear main seal and front cover seal alignment, reducing potential for leaks.

Vehicle Fitment: Application-Specific Precision

The ARP 207-5801 / AR8713 kit is engineered specifically for the Mitsubishi 6G72 engine family. Correct installation is paramount and requires machining clearance in the block for the stud bosses and potentially in the main caps themselves. Consultation with your machinist is required. Primary applications include:

Mitsubishi: 3000GT (1991-1999, all models, critical for VR-4 twin-turbo applications), Dodge Stealth (1991-1996, all models, critical for R/T Twin Turbo models). Later Model & SOHC Applications: Also fits many later-model SOHC 6G72 variants found in vehicles such as the Mitsubishi Montero, Endeavor, and Dodge Durango. It is the builder’s responsibility to verify physical clearance and block deck height compatibility for non-standard applications, as oil pan rail and windage tray modifications may be necessary.

Technical Specifications: The Blueprint of Strength

Installation Protocol & Final Recommendations

Installation of the Mitsubishi 6G72 ARP Main Studs is a machine shop operation. The block must be thoroughly cleaned, and the new studs should be installed finger-tight plus an additional 1/4 to 1/2 turn, using a thread sealant on the lower threads if they penetrate the water jacket. The main bearing bore must be align-honed or align-bored with the studs at their final installed height and the caps torqued to specification. This critical step compensates for any minute distortion induced by the significantly higher clamp load, ensuring a perfectly round and aligned bore. Never attempt to install these studs in a finished block without this machining step. Use only the provided ARP lubricant on the nut and washer interface to achieve the correct, consistent clamping force. For the serious builder aiming for a bulletproof 6G72, pairing these main studs with ARP’s head stud kit and a meticulously balanced rotating assembly is the unequivocal path to achieving both monumental power and unwavering reliability.