The Edelbrock head can be considered a bolt-on, cost-effective alternative to repairing factory castings and a part that has good performance potential. By contrast, the Blue Thunder heads approach the FE market from the other direction, bringing race-inspired features, and significant design revisions to a streetable package. The Blue Thunder heads focus on the more serious engine combinations, with larger displacements of 450 inches or more and RPM expectations beyond 6,500. These heads are delivered with valve seats installed but not machined. Guides are included but not installed. The consumer is responsible for correct machining, component selection, and assembly.
Blue Thunder offers multiple heads from a common external casting, which has evolved and been upgraded over the past few years. Current castings have a 16-bolt Cobra-Jet exhaust pattern, which is raised .400 inch relative to the head’s deck surface. The current offerings include heads with either a high-riser or a medium-riser intake port, neither of which truly resembles the factory parts that share those names.
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The current Blue Thunder heads require nine “long” head bolts (or studs) and a single “short” one in the lower center position. Factory castings in comparison, use five of each length. ARP offers a stud kit specifically for the Blue Thunder heads. Each head-bolt position has a pressedin hardened washer to prevent galling or distortion. All fastener holes have stainless-steel thread inserts.
Rocker mount holes are provided for multiple systems, both factory and aftermarket. Four 3/8 -16 holes are in the normal FE locations, along with eight 7/16 -14 holes that are aligned with the valve centers, as is common in most other engines. Rocker-mounting positions are raised and require the shorter highriser pedestals for factory-style systems. The thread inserts are recessed to allow milling of the rocker-mounting surface if needed for geometry adjustment. TD Machine offers a bolt-on rocker system that utilizes the additional fasteners and “throughthe- pushrod” oiling to address weaknesses inherent in the factory setup when run in race applications with high spring pressures.
The more popular medium-risercasting uses a large CJ/low-riser-sized port opening with the port floor set at the Ford medium-riser position— descriptively closer to being a raisedport Cobra Jet head. The as-cast port is large and well shaped, and can be run unaltered in 482-ci engines making more than 700 hp. The large port opening does limit intake manifold selection—only the Blue Thunder dual-plane intakes and the Edelbrock Victor have enough material to match the runner size without welding.
The Blue Thunder high-riser port is intentionally cast small, so that the engine builder can extensively port it by hand or CNC machine. As delivered, the head has a port opening roughly the same size as a Ford medium-riser head, but with the roof set to the high-riser position— descriptively more like a raised-port medium-riser head. In professional port work I have seen, examples of this casting reach 400 cfm in airflow— a range previously impossible with traditional FE castings. Blue Thunder chose to adopt the unique factory high-riser valve cover rail angle, which means intake selection is very limited, but the “Paquet” port intakes from Dove work well. At this build level, a fabricated sheetmetal intake is also a viable option.
Written by Barry Robotnik and Republished with Permission of CarTech Inc