Muscle Mustangs & Fast Fords
Supercharged Zex Appeal
It's Boost Versus Juice For This Tale Of A 2004 Cobra Terminator
Count me as one of the many who are very excited about the new 5.0 Coyote engine. Even if the best thing about it was the 5.0L name (I still have a soft spot for the original), the new motor would be very popular.
Lucky for Ford fans, the Four-Valve 5.0 is much more than a successful marketing ploy. Trick intake, variable cam timing and Chevy-topping performance (thanks no doubt in part to a lower curb weight), the new Mustang is an impressive piece indeed. If there is one complaint, it is the lack of forced induction. I know the Shelby GT500 is blessed with a blower, but I can't help wonder if, and when, we might get a supercharged 5.0.
Given the success of the Ford Racing Aluminator engine program, we should at least see low-compression versions of the Coyote available through the FRPP catalog. As great as the new 5.0 motor is internally, it still doesn't quite match the (seemingly) underrated Terminator motors offered from '03-'04. The supercharged 4.6L offered not only serious factory horsepower (and more importantly torque), but the ability to digest massive amounts of boost. Credit factory forged internals, topped by free-flowing cylinder heads and factory forced induction for the serious power potential.
We all know and love the '03-'04 Cobra motors. There is nothing quite so satisfying as having immediate boost followed by a surge of torque that accompanies a positive displacement supercharger. Impressive even in stock trim, the factory tune was purposely conservative, which meant there were bucket loads of power left on the table. Add a splash of good fuel, a more aggressive tune (altering both air/fuel and timing), and a few extra pounds of boost, and you had one pleasingly powerful Pony. In fact, the motor was so capable that eventually, the supercharger itself became the limiting factor in terms of maximum performance.
In all fairness to the Eaton Roots blower, it was never sized for 700-plus-horsepower, but the rest of the motor certainly seemed to be. Having pushed these factory engines well into the four-digit power territory, we can safely say Ford blessed these motors with a sizable safety margin. With this margin in mind, we ventured down two different paths in an effort to realize that potential.
The most obvious path was to maximize the existing supercharged combination and then add a dose of chemical warfare. The idea for round one was to take a stock '04 Cobra motor, crank up the boost on the Eaton supercharger and then hit is with a small does of nitrous oxide. In truth, we could have run considerably more nitrous, but the effort does illustrate the potential of the combination of boost and nitrous. Both are great at improving power production separ-ately, but combined they are even more formidable. The supercharged, Four-Valve test motor came from an '04 Cobra that had plenty of power, but as it turned out, very little talent behind the wheel. Crash damage destroyed a perfectly good Camaro killer, but the motor was still factory fresh.
Naturally, we were going to run this motor at a level higher than stock, but we also wanted to limit our modifications to external bolt-ons. With forged internals and free-breathing heads, the only thing missing (in our mind) was a set of performance cams. Tempting to be sure, we nonetheless resisted the urge to even remove the valve covers, and instead concentrated our attention on boost and juice.
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.
Photo GalleryView Photo Gallery
If some boost is good, then more must be better. Unfortunately for us, we were already pushing the limits of the factory Eaton, so more boost would require more blower. In our case, more came from a Kenne Bell twin-screw upgrade. Designed as a direct bolt-on replacement for the factory Roots blower, the Kenne Bell offered not only increased displacement (blowers available up to the new 3.6L), but improved efficiency which translates directly into lower charge temperatures. In truth, the factory air-to-water intercooler is effective at removing vast amounts of unwanted heat from the charge temperature. Less inlet air temp equates directly to more oxygen molecules, the essential building blocks of horsepower. The Kenne Bell was installed after swapping over the factory intercooler core. The blower was equipped with a 3.25-inch blower pulley to nearly match the 3.2-inch blower pulley run on the stock supercharger. The KB was run with the same Accufab throttle body, though the intake between the blower and throttle body differed between the two superchargers.
We were obviously hoping for more boost and power from the twin screw, and that's exactly what we got. Equipped with the 2.4L Kenne Bell supercharger, the peak boost pressure jumped to 16.5 psi at 6,500 rpm, and the power output followed suit. Though still climbing rapidly, we shut the party down at 6,500 rpm where the 4.6L produced 682 hp. Peak torque checked in at 594 lb-ft at 4,700 rpm compared to 506 lb-ft at 4,400 rpm for the stock blower. With a bigger blower and more boost, the Kenne Bell certainly offered more power than the stock combination, but a comparison is inevitable between the blower/nitrous combo and the boost-only set up. The Kenne Bell offered more peak power (682 hp versus 636 hp), but lost out in torque production (637 lb-ft to 594 lb-ft).
As indicated previously, these are simply two different methods of improving power and the test motor will certainly withstand much more of either (or both). The only thing better than having more power, is having more ways to achieve it. Whether you choose more boost or Zex appeal, either one makes a killer combo.
'04 Cobra-Eaton SC vs. Zex Nitrous (125 hp)Adding nitrous to any motor instantly transforms it into a serious contender, and this supercharged '04 Cobra motor was no exception. Despite being blessed with a supercharger, the '04 Cobra motor was the ideal candidate for nitrous. Equipped with forged internals and low compression, the 4.6L could easily handle the extra power offered by the Zex nitrous kit. Having run these Cobra motors near 1,000 hp in turbocharged form, they are more than capable of withstanding serious power levels. Literally at the push of a button, the Zex wet fogger kit improved the power output of the modified '04 Cobra motor from 533 to 636 hp, though the gains were as high as 127 hp elsewhere along the curve. For those looking for even more power, the Four-Valve Cobra motor would easily take another 100hp worth of nitrous.
After cranking up the factory Eaton supercharger with the pulley upgrade from South Florida Pulley Headquarters, we replaced the factory blower with a twin screw from Kenne Bell. Retaining nearly the same pulley combination (3.25 blower/7.5 crank), the peak boost pressure jumped from 12.1 psi with the Eaton to 16.5 psi with the Kenne Bell (2.4L). The improved efficiency and extra boost had a positive effect on the power output, as the supercharged Cobra motor now thumped out 682 hp and 594 lb-ft. As indicated by the graph, the power curve was climbing steadily and was well on its way to the 700hp mark had we elected to run the motor past 6,500 rpm. Pulley changes would certainly push this motor past 800 hp, while the new 3.6L blower from Kenne Bell can easily top 1,000 hp.