Bigger (stroker) motors can get away with slightly wilder cam profiles. Looking for both power and driveability, we chose a suitable grind from the Crane cams catalog. Crane is back in the performance valvetrain business and has a wide variety of powerful cam grinds for your 5.0L and 351W Ford. Its retrofit cam profiles were designed to work in blocks (like our 351W) not originally equipped with hydraulic roller cams. The dual-pattern, hydraulic roller cam from Crane offered a 0.584/0.595-lift split, a 240/244- duration split, and a 114-degree LSA. The cam was supplied with PN 36532-16 link-bar lifters and a set of Gold 1.6-ratio roller rockers.
To establish a baseline, the Crane cam was first combined with an Edelbrock Performer RPM Air Gap intake and Holley 950 Ultra HP carburetor. This was the classic carbureted combination, designed for performance street use. Sure, a single-plane Victor Jr. might make more peak power, but nothing offers the combination of torque and power of a solid dual-plane manifold for street use. Equipped with the dual-plane intake and 950 Ultra HP carburetor, the 408 Ford produced 530 hp at 6,000 rpm and 535 lb-ft of torque at 4,200 rpm. Torque production with the effective dual-plane induction system exceeded 525 lb-ft from 3,800 to 4,800 rpm.
After running the Edelbrock and Holley, off came the carbureted induction to make way for the eight-stack system from Procomp Electronics. The IR system was run with a Holley EFI using 75-lb/hr injectors, though Procomp Electronics does offer a stand-alone management system as well. The 75-pound injectors were fed by an Aeromotive A1000 fuel and regulator, though Procomp Electronics also offers these components to complete the injection system.
Installation was straightforward, requiring only the purchase of four intake studs for the center mounting holes. Each of the four end throttle bodies was designed to accept a TPS sensor, making wiring harness hookup a snap. The central vacuum fitting was conveniently located, allowing us to run a vacuum line to our 1-bar MAP sensor. The throttle linkage for dyno use consisted of a Morse cable hooked to a short throttle cable and the central bell crank. The throttle crank can be activated as a push or pull system.
One of the common misconceptions regarding the IR system is that the power comes from increased throttle area—the thought being more flow equals more go. Though the IR system does offer unrestricted flow, it is a combination of flow, equalized runner length, and lack of common plenum that accounts for the change in power compared to a traditional induction system. Thus, the polished aluminum, radiused air horns offered show, flow, and go.
Once installed and tuned, the Procomp Electronics system not only provided the expected performance upgrade (peak power numbers jumped to 572 hp and 560 lb-ft), but also a respectable idle (given the cam) and impressive throttle transition. WOT power is actually the easiest part of tuning (taking just 6-8 pulls total), but driveability can require many more hours, especially on an eight-stack (IR) system. The rock-solid throttle linkage minimized deflection, which helped produce synchronized throttle openings.
Individual-runner intake systems almost always look cool, and this system was no exception. What really made this stack attack shine was the combination of good looks, performance and ease of operation.
7 Hooker supplied the 1-3/4-inch...
7 Hooker supplied the 1-3/4-inch Super Comp headers. The headers were run in conjunction with a set of 18-inch collector extensions.
8 Run with the carbureted...
8 Run with the carbureted induction system, the 408 produced 530 hp at 6,000 rpm and 535 lb-ft of torque at 4,200 rpm. As expected, the dual-plane offered a broad, usable torque curve.
9 In truth, the Procomp Electronics...
9 In truth, the Procomp Electronics IR system will likely sell on looks alone. If that isn’t enough, the affordable pricing will be icing on the cake. Retail pricing is $3,499 for the complete system including lower intake, throttle bodies, polished stacks, throttle linkage, fittings, stand alone ECU, wiring harness, all sensors, injectors, fuel rails, adjustable fuel pressure regulator, fuel filter, distributor and gaskets. Systems will likely be sold at a lower cost online. As important as those two variables are in the purchasing decision, we wanted to know how well it worked.
10 The eight stacks offer...
10 The eight stacks offer unrestricted airflow, but the radiused air horns and equal runner length were ultimately responsible for the shape of the power curve.
11 One of the beneficial...
11 One of the beneficial features offered by the system from Procomp Electronics was the centrally located throttle assembly. This eliminated lengthy throttle rods that result in unbalanced (side-to-side) throttle opening.
12 The lower intake featured...
12 The lower intake featured a central plenum designed to provide a common vacuum source from all eight cylinders.
13 The throttle bodies all...
13 The throttle bodies all feature provisions to mount a throttle position sensor. This provides freedom to route the wiring harness.
14 Procomp Electronics even...
14 Procomp Electronics even supplied a set of 75-lb-hr injectors for our test. The dedicated aluminum fuel rails, mounts, and braided fuel line are all included in the kit.
15 Procomp Electronics offers...
15 Procomp Electronics offers its own stand-alone management system, but we elected to run the 408 with a Holley Dominator EFI system.
408 Stroker-Carb vs. Procomp Electronics IR
16 After tuning with the Holley EFI system, the new eight-stack injection from Procomp Electronics offered impressive power gains. The Stack Attack increased the power output of the 408 from 530 hp and 535 lb-ft of torque to 572 hp and 560 lb-ft of torque.
As is evident from the graph, the individual–runner induction system offered more than just a little power. The injection system from Procomp Electronics increased the power output of the 408 from 530 hp and 535 lb-ft to 572 hp and 560 lb-ft of torque. An extra 42 horsepower definitely makes this a worthwhile upgrade, especially when you consider the cost and cool factor. As well as your typical 5.0L EFI or carbureted system works, they just don’t have the wow factor like a trick IR setup.