ZRP-R-BMW-001-I-6 - The I-Beam Connecting rods for BMW 3.5L M5 & 3.6L M6 S38 are built from the finest raw materials 4340 high tensile steel with a specially optimized shape for high performance and extreme durability. The bushings are made from AMPCO 18 material, for excellent resistance to wear and fatigue and have radial groove acting as an oil reservoir. They are shot peened to relieve stress from the material and multi-stage heat treated to increase rigidity. The tight tolerances in the production process, ensure a perfect fitment while optimizing the oil clearances. Bend and twist is tightly controlled. Each rod includes ARP 2000 cap fasteners that are rated at 220,000psi, optional ARP L19 material 260.00psi available as an upgrade and the whole kit is supplied with ARP moly and full fitting instructions. Additional machining processes Dowel sleeves for perfect fit and accurate re-assembling Lipped Cap Relief for improved big-end integrity at extreme application Grooves in Thrust Face for weight reduction Technical Features of ZRP Connecting Rods I-Beam Shape for extra rigidity Two-Piece forging for great strength Shot Peening for improved fatigue life Magnaflux Inspection guarantees that the consistency of the forged material meets our high-quality standard Double ribbed caps for added support Multi Stage Heat Treatment for maximum strength, dimensional stability, and fatigue life. CNC machining for superior tolerances, precise as much as 0.0002" Center to center is maintained under .001" tolerance Finite Element Analysis (FEA) Computer generated stress analysis of con rods Optimal balancing for weight matched sets of ± 1gram