After our adventures with the 920hp Kenne Bell 4.6 motor, we suspected that this 800-plus-horsepower motor might benefit from the larger set of race headers as well. Swapping the 1 5/8-inch Hooker street headers for the 1 7/8 to 2 1/8-inch step headers supplied by AccuFab resulted in a sizable jump in power on this supercharged 5.4. Despite our trouble with the six-rib pulley system, the headers offered 35 hp at 5,600 rpm and showed consistent gains of 20-25 hp through most of the rev range. Replacing the dyno water running through the air-to-water intercooler with ice water netted an additional 30-35 hp. The lower charge temperatures had little effect on the boost supplied by the blower, but the increased air density provided an impressive power gain. The combination of the headers and ice water improved the power output of the 5.4 by as much as 55-60 hp. It's too bad the six-rib belt stopped us from successfully running the motor past 6,200 rpm. This combination would surely have exceeded 900 hp with an eight-rib or cog-belt system without changing the blower pulley to increase the boost.
In preparation for a top-speed event, Sean Hyland supplied this 5.4 Four-Valve motor specifically built for forced induction. The idea was to run the 5.4 with a Vortech YSI reverse-rotation blower supercharged at the maximum allowable boost/timing level available on 100-octane fuel. Naturally set to deliver maximum boost and flow, the YSI is capable of exceeding 1,200 hp, but our combination was designed for a top-speed event in which it would have to run on 100 octane. Thus, the boost level was kept reasonable to allow the motor to live at wide-open throttle for extended periods. Equipped with a 3.00-inch blower pulley and a 7.5-inch crank pulley, the supercharged 5.4 pumped out 843 hp and 689 lb-ft of torque. This was a considerable jump in power from the 434 hp and 387 lb-ft produced in normally aspirated trim. Unfortunately, the use of a six-rib belt presented a serious belt slippage issue that ultimately limited the effective operating range and power production of the supercharged combination.