Z1 uses Carrillo A-beam rods because they are plenty strong for most VQ35 Forced Induction applications and keep the weight down (489 grams).  These are the same rods Nissan Motorports chooses to sell as an upgrade. 

Carrillo rods are made in San Clemente California of a proprietary chrome/nickel/vanadium alloy known as Carrilloloy.  The materials and workmanship is second to none and they include high strength Carillo bolts