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.
Medium-riser and high-riser Blue Thunder heads share a common exhaust side. The older version of the heads had the 8-bolt FE pattern, while newer castings now require longer head bolts and have the 16- bolt Cobra Jet pattern for improved clamping force and high-performance use.
The Blue Thunder high-riser head is designed to be CNC ported, and it is shown here on the intake side. The Blue Thunder high-riser heads come with a fairly small port.
Here is a comparison between the Blue Thunder and Edelbrock mediumriser cast port openings using the gaskets as a reference. You can readily see the difference in port opening size and shape. The Blue Thunder is noticeably larger and rounded off compared to the sharpcornered Edelbroc
The combustion chamber on this Blue Thunder head has been profiled. The desired port and chamber shape is digitized, and then tool paths are programmed allowing the CNC mill to effectively duplicate the model.
The Blue Thunder medium-riser heads used to come with a small port, but are now shipped with a much larger port opening that is effectively ready to use. They still require a valve job and components to perform at their best.
Machining a CNC chamber. This is a first rough cut, which will be followed by a fine cut. CNC machining allows quick and exact duplication of a developed and proven port design or chamber profile.
A completely CNCported and polished Blue Thunder high-riser head is a pretty impressive piece to look at—and they run as well as they look. This head was installed on a 520-inch, 12:1 compression, dual-quad-equipped engine that made more than 770 hp.
These Blue Thunder pieces are race-oriented heads, and the differences between these heads and the traditional FE parts are readily apparent. Since these are heads intended for engine builders and specific high-performance applications, valve seats are installed but not machined. Guides are included but not installed, so the builder/owner needs to correctly machine the guides, select the correct components, and assemble the heads. These heads easily accommodate 450-ci-or larger displacement engines that can rev more than 6,500 rpm.
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 Ford FE 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
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