Run on the dyno, the FR500-inducted...
Run on the dyno, the FR500-inducted 4.6L made 435 hp at 6,100 rpm and a peak of 483 hp at 7,500 rpm.
Originally introduced in the Mustang in 1996, the Four-Valve modular motor recently gained a new lease on life when Ford introduced the latest and greatest 5.0L version. With the new Mustang sporting a 5.0L and the Shelby offering the supercharged 5.8L, you have to ask—where does that leave the old 4.6L?
Actually, the 4.6L Cobra motor is alive and well, for good reason. Though no aftermarket heads have become available, the factory stuff can be made to flow pretty well. With the proper porting, big cams, and a ported intake, you have the makings for one healthy beast—add cubes, like we did with our recent DOHC build, and you can crack 500 hp quite easily. Back that up with nitrous or boost and you're talking about really serious power.
One need only look at Accufab's John Mihovetz to see just how far you can take a 4.6L. With twin-turbo mod motors exceeding 2,000 hp, the 4.6L can still hold its own with the very best performance motors. And to illustrate what is possible on a normally aspirated 4.6L Cobra motor, we decided to subject one to a series of bolt-ons.
Probe Racing supplied a set...
Probe Racing supplied a set of flat-top pistons to duplicate the factory slugs. The pistons were used with a factory Cobra (steel) crank and forged rods. Note also the Fel Pro MLS gaskets and ARP head studs.
The idea was to first test a stock motor and then add performance components to illustrate how well the Cobra responded. The quad-cam arrangement on the 4.6L meant this would be best achieved on an engine dyno, though the head, cam, and intake swap could be accomplished in the car as well.
While a stock NA 4.6L Cobra motor would suffice, we already had a 4.6L test mule courtesy of Sean Hyland Motorports. The motor had seen plenty of abuse, having previously been subjected to all manners of normally aspirated and boosted modifications. Combine that with extended periods of inactive duty, and we decided the motor deserved at least a light hone and fresh set of rings.
L&R brought the short-block back to life, as well as sourcing us a set of stock Four-Valve heads to serve as our baseline. We already had stock cams from a previous test, so after the hone and new rings, the motor was reassembled using Fel Pro MLS head gaskets and ARP head studs. Odds are that this mod motor will eventually see boost, so the head gaskets and ARP hardware was money well spent.
The stock heads came off a low-mileage '01 Cobra and required only a clean-up before installation. Add in the stock intake and exhaust manifolds, and toss on a Meziere electric water pump, and we were in business.
1. The stock Cobra heads...
1. The stock Cobra heads were just freshened up and installed on the awaiting short-block.
Run with a FAST XFI, it produced 336 hp and 332 lb-ft of torque. Often considered a high-rpm motor, the Cobra produced peak power at just 6,000 rpm, while peak torque came at 4,900 rpm.
Having established a baseline, off came the stock heads, cams, and intake to make room for our upgrades. First on the list was a set of ported stock heads from Sean Hyland. In addition to full porting on the intake and exhaust, the heads were also treated to slightly larger valves and a valvespring upgrade that provided sufficient coil-bind clearance for the Comp cams we had planned. The spring upgrade also allowed the motor to rev safely to 7,500 rpm. The ported heads were combined with Comp XE262AH cams. The dual-pattern XE262AH cams offered 226 degrees of intake duration, 222 degrees of exhaust duration, and a 114-degree lobe separation angle to go along with the 0.425 lift (both intake and exhaust).
2. Both the stock and SHM...
2. Both the stock and SHM heads were treated to a set of Comp valvesprings. The spring upgrades allowed us to run these stock heads with aftermarket cams in the future.
3. All testing was run with...
3. All testing was run with the FAST XFI engine management system. The FAST made short work of tuning each new combination to (safely) maximize power production.
4. The stock Four-Valve was...
4. The stock Four-Valve was run with factory exhaust manifold, but we swapped them out in favor of Hooker headers on the modified Cobra motor.
5. Run in stock configuration,...
5. Run in stock configuration, the Four-Valve Cobra motor produced 336 hp and 332 lb-ft of torque.
6. First on our list of upgrades...
6. First on our list of upgrades was a set of ported heads from SHM. Though the stock Four-Valve heads flowed well, additional porting can unearth plenty of power.
7. The intake and exhaust...
7. The intake and exhaust ports were given the full treatment. Care must be taken not to port right through to a water jacket, but proper blending and bowl work can yield large dividends.
8. Our ported heads also...
8. Our ported heads also featured oversize valves to improve flow. At some point, the valves themselves become the choke point in terms of flow.
9. Working with the high-flow...
9. Working with the high-flow heads was a quartet of Comp cams. The XE262AH cams offered 0.425 lift (both intake and exhaust), a 226/222-degree duration split, and a 114-degree lobe separation.
10. The factory Cobra intake...
10. The factory Cobra intake was also the recipient of minor porting, though no change was made to the runner length.
11. We even tried a single-blade...
11. We even tried a single-blade Accufab throttle body, but the factory Cobra throttle body seemed more than sufficient.
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.
12. The heads and cams were...
12. The heads and cams were swapped with the engine still hot on the dyno. We made sure to degree in the new Comp cams as the Four-Valve motors are notorious for inaccurate cam timing.
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.
13. After swapping the heads,...
13. After swapping the heads, cam, and intake and adding the Hooker headers, we were rewarded with substantial power gains. The peak numbers jumped from 336 hp and 332 lb-ft to 435 hp and 409 lb-ft, with gains posted through the entire rev range.
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.
14. Having completed the...
14. Having completed the test of upgrades to our 4.6L Cobra, we decided to use the remaining dyno time for a few extras, the first being this FR500 intake manifold.
15. Not only did the FR500...
15. Not only did the FR500 intake offer lightweight magnesium construction, but also dual-runner operation.
16. Shown from the bottom,...
16. Shown from the bottom, the dual runners are evident. Actuators are used to open the throttle blades that allow the motor to breathe through the shorter runners. Since long runners improve power down low and short-runners higher in the rev range, the FR500 (theoretically) offered the best of both words.
17. Our tired 4.6L Cobra...
17. Our tired 4.6L Cobra test motor needed a little work before making any more dyno runs. Accufab’s John Mihovetz was kind enough to lend his knowledge and experience to our effort.
18. The final test of the...
18. The final test of the afternoon was to install this trick Nozzle NOS system on the factory Cobra intake.
18b. Though a simple single-fogger...
18b. Though a simple single-fogger nozzle system would work equally well at this power level, the nozzles offered even distribution and flat out looked cool on the mod motor. Run with jetting to provide 100 hp, the NOS system improved the power output from 435 hp and 409 lb-ft to 544 hp and 623 lb-ft of torque.
Stock vs. Modified - Graphs tell so much more than simple peak power numbers. Adding the ported heads, intake, and Comp cams to the 4.6L, Four-Valve motor offered dramatic power gains. The peak power outputs jumped from 336 hp and 332 lb-ft of torque to 435 hp and 409 lb-ft. The combination improved power output through the entire rev range, with sizable torque gains coming down as low as 3,500 rpm. Credit the time spent degreeing the cams for some of the additional power.
Modified 4.6l 4V Intake Test--Ported Stock vs FR500 - Though no longer available, we had access to one of the dual-runner FR500 intake manifolds previously offered by Ford Racing. We tested the intake in short-runner form only, meaning we were most concerned about maximizing peak power. The short-runner intake performed as expected, allowing the motor to make peak power at 7,400 rpm instead of 6,100 rpm. The result was a jump in peak power to 483 hp, though the FR500 lost out to the factory intake below 6,000 rpm
Modified 4.6l 4V-NA vs NOS Nitrous (100hp) - After removing the FR500 intake, we had one final test to run. A few years back, NOS had shipped a set of nozzles that combined the nitrous and fuel in unique fittings designed to house the factory injectors. Given the limited amount of nitrous we used on this test, the same power gains could be expected from a simple single-fogger nozzle placed in the throttle body or air intake, but we liked the even distribution offered by the Nozzle setup. After installation of the Nozzles on the ported stock intake, we ran with jetting to provide an additional 100 hp. The result was a jump from 435 hp to 547 hp, with torque up from 409 lb-ft to 526 lb-ft.