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Four-Valve Modular Engine Upgrades - Cobra Crankup
Testing ported heads, cams, and intake upgrade—plus nitrous—on a 4.6L Cobra Mod mill.
A huge thanks goes to John Mihovetz for providing the necessary tools for performing the cam surgery and assistance with dialing them in. Without the valvespring compressor, custom piston stop (to precisely locate TDC), and associated components, we would never have been able to degree the cams properly.
While the main components are very similar to the Two-Valve GT motor, the Four-Valve also featured a secondary drive assembly from the exhaust cam to the intake. This secondary chain drive required a second pair of cam sprockets and a dedicated chain tensioner. The cam installation also required removal and compression of all 32 of the hydraulic lifters. In the end, the Four-Valve 4.6L cam installation was not terribly difficult, just time consuming.
The ported heads and XE262AH cams were combined with a ported stock intake, also from Sean Hyland, but no changes were made to alter the runner length of the factory intake. We also tried a larger throttle body, but at this power level, the stock throttle body seemed more than adequate.
The final performance upgrade included Hooker headers to replace the factory exhaust manifolds. Since we were looking for all the extra power we could find, the headers were a natural upgrade. After the upgrades and a tweak in the tune, output jumped to 435 hp and 409 lb-ft of torque. Not only did the upgrades improve the power output by just over 100 hp, but the torque peak was up 80 lb-ft. In fact, the power output was up through the entire rev range.
Having made all of the changes at once, we still had some daylight to burn and a healthy Four-Valve just begging for more mods. Despite not being offered by Ford Racing any longer, we decided to pull out an FR500 intake manifold we had stashed away. The FR500 is unique—not only is it made of lightweight magnesium, but it also offers dual runners. The design combined one set of long runners to bolster low-speed power with a set of short runners to enhance the top end. Unfortunately, we didn't have the actuators to switch between the long and short runners, and were instead forced to run the intake with the short runners activated. Looking primarily for peak power numbers anyway, the FR500 increased the output of the 4.6L to 483 hp at a lofty 7,400 rpm.
For the last hurrah, we added nitrous. Though a simple wet fogger system would suffice, we dusted off an old Nozzle system from NOS. We like the equal distribution offered by the individual-port system, as well as how cool the thing looks once installed. The system features individual nozzles that are positioned between the injectors and receiver holes in the intake manifold. For this test, we removed the FR500 and reinstalled the ported stock intake.
Like most systems, the NOS kit is adjustable using different nitrous and fuel jets. With jetting designed to supply an additional 100 hp, we pushed the button and were instantly rewarded with peak numbers of 547 hp and 526 lb-ft of torque. Big numbers with nitrous are so easy, just make sure you have plenty of fuel and retard the timing as we did by 3-4 degrees at this power level. Looking back at how easy it was to increase the power output of the Four-Valve, we'd say the 4.6L has a solid future in the performance industry.