We also stepped up the cam profile to ensure the 408 offered plenty of power in injected form. The 408 was still equipped with the AFR 205 heads left over from the head test. We would like to have run the new CNC-ported TFS TW heads, but we (meaning I) got lazy and didn't perform the head swap (which also required a valvespring upgrade) before installing the new TFS intake. The XFI cam profile checked in at 238/248 degrees at 0.050, while the lift measured 0.579 inch with a 114-degree lobe separation angle. Hooker headers, an MSD ignition, and the FAST management system were also employed.
The highlight of the EFI stroker was the fuel-injected intake system. We have tested the new Box R intake from Trick Flow Specialties on a 331 stroker, but we have not combined the upper intake with the 351W-based lower manifold. You may remember the Box R intake was tested against the TFS R upper intake on the 331 stroker, with excellent results. The Box R upper intake offered a significant gain in upper-rpm power without the usual sacrifice in low- and midrange torque (compared to the TFS R intake).
A peek inside the two-piece upper intake reveals why it works so well in stroker applica-tions. The first thing you notice is the massive throttle opening, as the Box R was set up to accept a 90mm throttle body. We obliged the intake by supplying the opening with a 90mm throttle body from Accufab. Other beneficial features included generous port volumes with a smooth radius on the entry to maximize air-flow (while minimizing turbulence). Unlike previous box-style intakes, the upper intake featured extensions of the runners rather than simply ending them at the junction of the upper and lower intake. While maximizing the airflow through the runner is important, so is providing proper runner length to optimize the reflected wave tuning. The supercharging effect offered by the reflected waves dramatically improves the power production offered by an intake design.
The lower intake was designed to not only fit on the taller-decked 351 Windsor, but also allow the Box R (or other TFS upper intakes) to bolt right on. In addition to accepting the different TFS upper intakes, the 351W lower manifold also features provisions for the IAT (inlet air temp), ECT (engine coolant temp), and factory fuel injectors. The manifold was drilled and tapped to easily accept the factory fuel rail, thermostat housing, and heater hose assembly. Unlike a number of aftermarket intakes, the TFS Box R was easy to bolt onto the lower intake and did not interfere with the factory (or our taller aftermarket) valve covers. The upper intake was drilled and tapped for a number of different vacuum lines (for the fuel pressure regulator, brake boost, and interior accessories).
We also liked the O-ring seal used between the two halves of the upper intake and the fact that the Box R did not interfere with the large (factory) distributor cap. There is nothing more frustrating than installing an intake in your driveway and having to grind the cap or valve cover to get it to fit properly.
Given the displacement offered by the CHP 408 stroker, we were hoping to exceed 500 hp with the TFS EFI system. The Box R upper intake and 351W lower manifold were installed on the 408 with a set of 36-pound injectors using a Vortech aluminum fuel rail. The FAST engine management system was tuned to provide an air/fuel ratio of 13.0:1 (12.6:1 at the torque peak) and total ignition timing of 32 degrees. After tuning, we were rewarded with peak power numbers of 525 hp (at 6,300 rpm) and 530 lb-ft of torque at 4,500 rpm. While the peak power occurred at 6,300 rpm, note that the torque peak occurred at just 4,500 rpm. Having nearly 2,000 rpm between the peak torque and horsepower numbers meant the injected 408 provided a broad powerband. Torque production from the 408 exceeded 500 lb-ft from 3,600 rpm to 5,400 rpm. Torque production exceeded 450 lb-ft all the way to 6,100 rpm. With 525 hp on tap, there is one injected 408 that can provide a knock-out punch. Now throw in the impressive torque curve and extra efficiency of the EFI system and you have the makings of a serious and reliable street stroker.