Skunk2 Racing Ultra-Series Race Manifold Primary Fuel Rail - Honda B Series Engines Engineers at Skunk2 Racing have developed primary and secondary fuel rails for the popular Ultra-Series Race intake manifold. Skunk2&rsquos newest fuel rails are made from 6061-T6 aluminum, features large 0.669-inch internal bores and -8 AN o-ring thread, and can support up to 1,200hp. Product Notes Supports Up To 1,200 HP 0.669&rdquo Internal Bore -8 AN O-Ring Thread Compatible with E85 and Methanol Requires the use of an external regulator.