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Supercharged Zex Appeal
It's Boost Versus Juice For This Tale Of A 2004 Cobra Terminator
The first step was to increase the boost pressure supplied by the factory supercharger. To this end, we replaced the factory crank and blower pulleys with a combination from South Florida Pulley Headquarters. The crank pulley was upgraded with a 7.5-inch version, while the stock blower pulley was replaced by an adjustable set. Our testing was run with a 3.2-inch blower pulley, as the smaller 3.0-inch blower pulley did not net us any more peak power. This was possibly due to belt slippage, though the dropping boost curve offered by the Roots blower with every other pulley combination was a clear indication that we were pushing the flow and power limits of the stock blower. Wanting to minimize any inlet flow restrictions, we also replaced the factory intake and throttle body with high-flowing units from Accufab. This was an important step, as positive displacement superchargers are very sensitive to inlet restrictions. Any vacuum present in the inlet system will result in less boost and power provided by the supercharger.
The '04 Cobra motor was tuned to perfection using a FAST management system, and all testing was run with Hooker long-tube headers feeding 18-inch collector extensions. In our effort to maximize power, all testing was run using 100-octane fuel, though we suspect it would perform equally well (and safely) on 93-octane pump gas. In anticipation of our elevated power level, we replaced the factory injectors with 65-pounders from FAST, and filled the crankcase with fresh Lucas 5W-30 synthetic oil. Run in this configuration, it produced 533 hp and 506 lb-ft of torque. The peak boost reading was 12.1 psi, though the boost dropped off to 11.2 psi at the power peak. Torque production exceeded 500 lb-ft from 3,000 rpm (and lower had we started our test earlier in the rev range) to 4,800 rpm. These were serious numbers from a motor displacing just 4.6 liters, especially given that the motor was stock beneath the blower.
Now that we had our boost, it was time for some juice, which came from the folks at Zex, who supplied a universal wet EFI system. Designed to add 75-125 hp to just about any EFI motor, the nitrous kit offered a number of trick features, including a controller that actually learned the voltage curve of the TPS. This feature insured the nitrous system could not be accidentally activated until it was armed and the motor was running at WOT. Hook up was easy, especially on the dyno-we drilled and tapped the Accufab intake to accept the single fogger nozzle that combined both fuel and nitrous. All that was necessary was to run a dedicated fuel line from the fuel regulator and the nitrous line from the bottle. Wiring the controller was easy, as were the steps to allow the system to learn the TPS voltage. When all was said and done, we engaged the nitrous to the tune of 636 hp and 637 lb-ft of torque. Running the nitrous actually increased the peak boost pressure reading to 13.3 psi. Torque production now exceeded 600 lb-ft from 4,400 rpm to 5,400 rpm and never dipped below 500 lb-ft whenever the nitrous was engaged. Boost and juice obviously work well together (nitrous acts as an intercooler) and we wouldn't think twice about stepping up this combination with another 100-125 hp worth of nitrous.
It's no surprise that motors respond well to nitrous, but it is nice to know that it works well even on supercharged combinations. Still, for those looking to eliminate the inconvenience of filling the nitrous bottle, we decided to offer up a second option.