Manley TurboTuff I Beam Rods are forged, aircraft quality 4340 alloy steel, fully machined in the USA. The highest horsepower Subaru applications are appropriate for the TurboTuff I-Beams. After machining and magnafluxing to check for imperfections, each rod is shot peened to increase strength even further. Standard I-Beam kits received ARP 2000 rod bolts and upgraded kits (with R6 in the part number) receive ARP 625+ rod bolts for further strength and reinforcement. Manley supplies the highest horsepower Subaru engines with rods, pistons, and more.