BC0136 – Mitsubishi 4B11 Evo X Stroker Kit – 98mm Stroke/I-Beam Extreme Rods (I Beam)

In the relentless pursuit of dominant powerband characteristics and unyielding structural integrity, the Brian Crower BC0136 Stroker Kit stands as a definitive engineering solution for the Mitsubishi 4B11 platform. This is not merely an assortment of parts; it is a harmonized system engineered to transform the displacement and durability ceiling of the Evolution X’s powerplant. By integrating a precision-forged 98mm stroke billet crankshaft with purpose-built I-Beam Extreme connecting rods and custom forged pistons, the BC0136 kit facilitates a calculated overbore and stroke increase to approximately 2.5 liters. This displacement gain is the foundational mechanic for generating massive, responsive torque and extending power production deep into the rev range, a critical advantage for competitive motorsport applications, forced induction dominance, and achieving uncompromised street performance. Every component is subjected to Crower’s exacting metallurgical and machining standards, resulting in a rotating assembly that is not just stronger than OEM, but is optimized for the elevated cylinder pressures and inertial stresses of high-output builds.

The Engineering Philosophy: Displacement as a Foundation

The core objective of any stroker kit is to increase engine displacement, which directly influences an engine’s volumetric efficiency and torque potential. The BC0136 executes this with surgical precision. The 4B11 billet crank, the heart of this system, is CNC-machined from a premium-grade 4340 steel billet. This manufacturing process, superior to traditional forging or casting, allows for grain flow that follows the final contours of the crank, eliminating stress points and creating a component of exceptional torsional strength and harmonic dampening. The increase in stroke from the factory dimension to 98mm moves the piston further within the cylinder bore on each cycle, drawing in a greater mass of air and fuel. When combined with the appropriate cylinder head work, turbocharger, and fuel system, this larger “air pump” establishes a more robust platform for power, often allowing for the same peak horsepower figures to be achieved at lower boost pressure, thereby reducing thermal load and increasing overall engine efficiency and safety margin. For a deeper technical dive into the benefits and considerations of stroker engines, refer to this authoritative resource on stroker engine fundamentals from industry experts.

Core Component Breakdown: A Symphony of Forged Strength

The efficacy of the BC0136 kit hinges on the synergistic performance of its three primary components: the crankshaft, connecting rods, and pistons. Each is selected and manufactured not just for individual strength, but for collective balance and longevity under extreme conditions.

Billet 4340 Steel Crankshaft (98mm Stroke)

This is not a reground or welded OEM unit. The Brian Crower 4B11 billet crank is created from a solid block of 4340 chromoly steel, heat-treated to a core hardness of 32-34 Rc. It features precision-micro polished journals and radii, Tuffriding surface treatment for superior wear resistance, and is fully counterweighted and balanced to exacting tolerances. The 98mm stroke is the critical dimension that defines the kit’s displacement increase, requiring the complementary components to be specifically engineered around it.

BC Extreme I-Beam Connecting Rods

To articulate the increased stroke, Crower supplies its Extreme series I-Beam Extreme rods. Machined from 4340 chromoly steel billet, the I-beam design is chosen for its optimal balance of weight, strength, and rigidity in high-RPM, high-load applications. They feature ARP 2000 cap screws (or upgradeable 625+ options) as standard, precision honed big and small ends with bronze bushed small ends for optimal piston pin fitment, and are shot-peened for enhanced fatigue life. These rods are built to manage the increased piston speed and inertia generated by the longer stroke without flex or failure.

Custom Forged Pistons

Completing the assembly are the 4B11 custom pistons. These are not generic shelf pistons; they are specifically forged from 2618 aluminum alloy to match the increased deck height requirement created by the stroker crankshaft and longer rods. They feature a robust design with optimized ring land placement for reliability under high boost, deep valve reliefs to accommodate aggressive camshaft profiles, and are coated with a proprietary skirt coating to reduce friction and scuffing. Available in a standard overbore size (typically +0.5mm or +1.0mm from the factory 86mm bore), they finalize the displacement calculation, bringing the final swept volume to roughly 2.5 liters.

Performance Benefits & Application Goals

The integration of the BC0136 Stroker Kit delivers a transformative set of advantages for the serious 4B11 builder:

• Substantial Torque Multiplication: The increased displacement directly translates to a broader, flatter torque curve. Expect a significant gain in low-end and mid-range responsiveness, which translates to faster turbo spool, reduced lag, and devastating acceleration out of corners or from a roll.
• Enhanced Powerband Width: By increasing displacement, the engine can often make target horsepower numbers at a lower RPM, reducing stress on valvetrain and rotating assembly components. Alternatively, it provides a stronger foundation to safely extend the powerband further with supporting modifications.
• Unmatched Rotating Assembly Durability: The billet crankshaft and 4340 I-beam rods represent a monumental increase in fatigue strength and yield limit over factory components. This built-in safety margin is critical for high-boost, high-RPM, and nitrous or methanol applications.
• Platform for Extreme Power: This kit is the cornerstone for builds aiming reliably for 600whp and far beyond. It removes the displacement and bottom-end strength as limiting factors, allowing the tuner to focus on airflow, fuel, and ignition optimization.
• Improved Driveability (When Tuned Correctly): The added low-speed torque can make a highly-modified Evo X more manageable in street driving conditions, reducing the need for excessive boost to get moving.

Vehicle Fitment & Installation Critical Notes

Primary Application: This BC0136 kit is engineered specifically for the Mitsubishi 4B11 engine found in the 2008-2015 Lancer Evolution X (CZ4A chassis).

Installation Mandates: Installing a stroker kit of this caliber is a precision engine-building operation, not a simple bolt-on. It requires complete engine disassembly (long block). Critical steps include:
Machine Work: The cylinder block must be bored and honed to the exact piston specification with proper deck surface preparation. The crank journals must be measured and the block align-honed with the new main studs installed.
Balancing: The entire rotating assembly (crankshaft, rods, pistons, pins, rings, and harmonic damper/flywheel) must be dynamically balanced by a qualified machinist. The supplied crank is neutrally balanced, but final balancing is essential for smooth, high-RPM operation.
Clearance Verification: Piston-to-valve clearance, piston-to-deck height, and rod-to-cam/crank case clearance must be meticulously checked and documented during dry assembly. Valvetrain geometry should also be verified with the new deck height.
Supporting Modifications: This kit demands a comprehensive build. Upgraded cylinder head hardware (head studs), a performance valvetrain capable of the target RPM, a fuel system scaled for the increased airflow, and a turbocharger and tuning strategy to leverage the new displacement are all necessary to realize its full potential.

Technical Specifications: BC0136 Stroker Kit