Richard Holdener
November 1, 2007
Bolting on the right intake manifold can make or break your 5.4L Four-Valve combination. Like the cam profiles, the intake design must be chosen to work in the desired rpm range.

Given the amount of time and effort that goes into the design of a factory intake manifold, it's not surprising that it's sometimes difficult to improve upon the stock induction system. Stock induction must make good power for the application, but it must also produce a broad powerband, good fuel economy, fit under the stock hood with all the necessary components, and be inexpensive to produce, as hundreds of thousands will need to be made.

Obviously, each factory intake for any application was designed with much more than just peak power in mind. Take the 5.4L Navigator, for instance. Does it make sense to top a 5.4L Four-Valve modular truck engine with an intake that will pull strongly to 8,000 rpm? While some of us would certainly like a 5.4 Cobra R motor powering everything with a Blue Oval, the reality is that such a combination is not ideal for the heavy SUV application. What the sport/ute really needs is a motor that offers plenty of low-rpm torque production.

For Ford, the first order of business was to supply it with the largest mod motor available, namely the 5.4. To further improve the response rate of the motor and help get the hefty curb weight properly motivated, Ford saw fit to equip the 5.4 with an intake design that would enhance low-speed power production. Ford even went to great design lengths to equip the long-runner intake with a dual-plenum divider to broaden the torque curve. In short, it optimized the engine combination for the intended application, not for just peak horsepower.

The application-specific nature of an intake design means that only one absolute is possible, and there's no one ideal intake for every conceivable application. Arguments to the contrary amount to nothing more than a big waste of time.

Our test motor was a modified 5.4L supplied by Sean Hyland Motorsport. The 5.4L Four-Valve motor was equipped with ported Navigator heads, SHM Stage 2 and 3 cams, and a forged rotating assembly. Loyal readers will remember that this same motor produced 1,002 hp at just over 17 psi with a twin-turbo kit from HP Performance last month.

As trick as the Cobra R, the Boss 290, or even the Sullivan Performance intakes are, they're not all things to all people. Neither of the three powerful intakes listed are ideal for an otherwise-stock Navigator motor powering a heavy SUV. By the same token, the stock Navigator intake isn't the ideal choice for a 5.4 race motor running effectively above 7,000 rpm.

What's needed for any car or truck owner is an intake that provides the best possible power curve in the intended rpm range. This usually means sacrificing power elsewhere in the curve, but such trade-offs are inherent in any design. On rare occasions, it's possible to enhance the power output of a combination throughout the rev range, but more often than not, power gains at the top of the rev range will be accompanied by losses down low. The key is to minimize the trade-offs associated with the gains. Please note that the effective operating range is still in effect with the presence of boost, as the intake design still dictates where the motor makes power, even with a turbo or blower.

Some may think we ran the intake testing on this 5.4 Four-Valve to illustrate the ideal intake choice, but nothing could be further from the truth. We ran this test to illustrate the effect of various designs on the power curve. Not one in the bunch can be considered the "best" intake, as it's always possible to make more power or more torque at a given engine speed with another combination. This doesn't even take into account the cost or availability factors. Sure, the Boss 290 intake performed well, but try getting your hands on one-if you do, check out how much it costs. If price was no object, we'd all have custom intakes machined for our motors that were idealized for our combination, but cost is always a major consideration when choosing a manifold, or any performance upgrade, for that matter.

5.4L Four-Valve Stock Navigator Intake
Not surprisinglY, the stock Navigator intake manifold looked right at home on the modified 5.4L Four-Valve motor. Though the factory Navigator intake was equipped with an electronic dual-plenum divider, we didn't have the ability to activate this during testing, and it was run in the open (connecting both plenums) position. We suspect from previous testing on the 4.6L Two-Valve truck intake (which was likewise equipped), that the dual-plenum trickery is used to further enhance low-speed torque production. Equipped with the Navigator intake, the 5.4L produced 426 hp and 411 lb-ft of torque with a torque curve that exceeded 375 lb-ft from 3,000 rpm to 5,900 rpm.

5.4L Four-Valve Stock Navigator vs. Kar Kraft
What happens when you remove the factory upper intake and replace it with a trick carbureted piece? Removing much of the runner length had the expected result of reducing torque production lower in the rev ranges, but the carbureted upper intake had a positive effect on peak power production. Compared to the factory (long-runner) Navigator intake, the Kar Kraft-carbureted conversion lost power up to 4,600 rpm but offered a gain of 22 hp on the top end. We really liked the look of the carbureted upper intake. The Kar Kraft intake went a long way toward transforming the 5.4L Four-Valve motor into a Boss 429 look-alike.

To establish a baseline, we ran the factory Navigator intake on the modified 5.4L. Equipped with the Navigator intake, the low-compression 5.4L produced 426 hp and 411 lb-ft of torque. As expected, the Navigator intake offered exceptional (and unequaled) low-speed torque production.

The ease of installation is another consider-ation, as the Kar Kraft-carbureted upper intake was by far the easiest to install. In most cases, enthusiasts are willing to give up a few horse-power and lb-ft of torque for things like price, availability, and ease of installation. The same can be said of the Wow! factor, as lifting the hood to reveal something wild, different, and/or impres-sive is usually worth a few extra bucks.

To illustrate the effect different intake designs have on the power curve, and to cater to the Mustang (or other fast Ford) crowd that has embraced the displacement and attending power gains offered by the 5.4, we decided to run a few comparisons. The first order of business was to build a suitable test motor. Actually, this part of the equation was already taken care of, as we still had our modified 5.4 from Sean Hyland Motorsport.

This 5.4 was used previously with a Vortech supercharger and then again with a pair of turbos from HP Performance to the tune of 1,000 hp. Still in excellent condition, the low-compression 5.4 features a forged reciprocating assembly topped off with a set of ported Navigator heads and Stage 2 and 3 SHM cams. The idea was to run the modified engine with a pair of factory intakes and then with a variety of aftermarket versions. Included in the list were the factory Navigator and Boss 290 intakes along with a carbureted upper intake from Kar Kraft, a replacement intake from Sullivan Performance, and even the author's own adjustable design. Thanks go out to the guys at Sullivan Perfor-mance and Kar Kraft for getting the intake to us in time for testing, and going the extra mile to provide a manifold we could hack up in a quest for the necessary intake flanges.

First up was the stock Navigator intake. From the factory, the intake featured long runners and dual plenums. Much like the 4.6 Two-Valve used in truck applications, the dual plenum was separated by a divider that was electronically operated. We chose to eliminate this system by wiring the divider in the open position. (For those interested in the effects of the divider, check out the author's book, Building 4.6L/5.4L Ford Horsepower, available from www.Cartechbooks.com.) The two-piece (long-runner) Navigator intake featured a dual-blade throttle body and a dedicated water crossover. This was replaced by the more familiar tubular steel crossovers employed on the Four-Valve Cobras for the other intakes. Equipped with the Navigator intake, the 5.4L produced 426 hp and 411 lb-ft of torque. Torque production exceeded 400 lb-ft, from 4,000 rpm to 5,400 rpm, and exceeded 375 lb-ft at 3,000 rpm. Given its intended application, the Navigator intake performed admirably and, as we were to find out, it offered the best low-speed torque production of any combination tested.

Since we started with the two-piece Navigator, we decided the easiest route was to replace the factory upper intake section with the system supplied by Kar Kraft. Basically a replacement for the entire upper intake, the new manifold from Kar Kraft allowed us to replace the throttle body and EFI setup with a simple Holley or Barry Grant four-barrel carburetor. It should be noted that it's also possible to run the Kar Kraft upper intake with the four-hole throttle body and retain the injectors in the lower manifold, running it as an EFI system. Time did not allow for a test in that configuration, however. While the EFI system would obviously provide better control of the air/fuel ratio, the carburetor might offer improved performance thanks to the charge cooling offered by fuel atomization.

5.4L Four-Valve Stock Navigator vs. Sullivan Performance
Next on the list was the carbureted/EFI intake from Sullivan Performance. Like the system from Kar Kraft, it was possible to run the Sullivan intake in either carbureted or EFI configuration. Had sufficient time been available, we would have run both intakes in both configurations, using a four-hole throttle body in place of the carb, but no such luck. We ran the Sullivan intake in EFI configuration with a 90-degree elbow and 90mm AccuFab throttle body. You'll remember that this intake was employed on the twin-turbo 5.4L that produced 1,002 hp at just 17 psi. Equipped with the Sullivan intake, the 5.4L Four-Valve produced 458 hp and 395 lb-ft of torque. The short runners in the Sullivan intake lost torque to the factory Navigator intake but picked up peak power. In retrospect, we should have run the test motor higher than 6,500 rpm to give the Sullivan a fair shake, as this design offered impressive high-rpm power.

Basically a single-plane carbureted intake, the manifold from Sullivan Performance was run with injectors and a 90-degree elbow fed by a 90mm Accufab throttle body. We hoped to run it with a carb as well to demonstrate the power differences offered by the fuel atomization (which cools the intake charge), but time did not allow for such testing. Equipped with the Sullivan intake, the 5.4L produced 458 hp and 395 lb-ft of torque.

Kar Kraft also offers a dual-quad upper intake for this application as well, and we hope to test one of those in the near future. Removing the upper intake dramatically shortened the intake runner length, which had the effect of reducing low-speed torque but increasing top-end power. The peak numbers registered by the Kar Kraft upper and 750 carb were 448 hp and 407 lb-ft of torque. Check out the graph to see the overall effect on the power curve.

Next up was the intake from Sullivan Performance. We have built and/or covered a number of high-horsepower modular motors equipped with the Sullivan intakes, including our own 1,000hp 5.4 and the amazing 1,300hp blower motor built by John Mihovetz. The Sullivan intake is basically a single-plane carbureted manifold equipped with provisions for injectors.

Like the Kar Kraft upper intake for the Navigator lower, we could have run the Sullivan intake in either carbureted or injected form, but we elected to run it with a 90mm throttle body and matching 90-degree elbow. As with all of our testing, the FAST management system was used to control the fuel and timing curves (timing only with the Kar Kraft upper). The short runners on the Sullivan intake offered plenty of top-end power but lost out to the long-runner Navigator intake lower in the rev range. From the looks of the power curve, we know the Sullivan intake had more rpm to offer, but we kept the maximum engine speed at 6,500 rpm on the long-stroke 5.4L. Equipped with the Sullivan intake, the mod motor produced 458 hp and 395 lb-ft of torque but was still rising at our self-imposed shut-off point.

5.4L Four-Valve Stock Navigator vs. Boss 290
The Boss 290 intake was actually a factory Ford piece. An offshoot of the ultimate 5.4L Four-Valve intake-the Cobra R-the Boss 290 is offered on 5.4L-powered vehicles in Australia.

While a factory offering, the Australian manifold is difficult to come by and, as such, is quite expensive. Unlike the original Cobra R, the ports on the Boss 290 were sized to run on the smaller '03 Cobra heads and were slightly smaller than the ported Navigator heads run on our test motor. The Boss 290 intake also relied on a single (round) throttle body rather than the conventional oval or dual-port Cobra version. The cross-ram design looked impressive especially with the upper plenum cover removed.

With no factory throttle body available for testing, we were forced to rely on an aftermarket throttle body for an LS1. Equipped with the Boss 290, the 5.4L produced 457 hp and 420 lb-ft of torque. Compared to the other intakes tested against the Navigator manifold, the Boss 290 offered slightly longer runners, and this showed in the results. The Boss 290 intake matched the output of the Navigator at 4,000 rpm and pulled away steadily thereafter. As with all the others, the Boss 290 lost out to the Navigator below 4,000 rpm.

5.4L Four-Valve Stock Navigator vs. Custom Intake
The great thing about building an adjustable intake is that it's possible to find out exactly what the engine combination responds to. Using this principle, we were able to adjust the custom intake to produce not only 456 hp, but also the highest peak torque of the bunch, a solid 433 lb-ft of torque. True to form, the custom intake did not match the torque production of the factory Navigator intake below 3,600 rpm. From there on up, the custom intake offered both more power and torque. Torque production from this design exceeded 400 lb-ft, from 3,800 rpm to 5,950 rpm.

We were anxious to see the battle of the factory Fords, with the Navigator intake slugging it out with the Australian Boss 290 intake. The Boss 290 intake featured slightly smaller ports than those on our ported Navigator heads, but the intake design offered longer runners than the Sullivan or Kar Kraft manifolds. This extra runner length showed in the results, as the Boss 290 produced the best torque number of the bunch (until running our final competitor) with a peak reading of 420 lb-ft.

Basically a mini Cobra R manifold, the Boss 290 from Australia was a factory Ford piece. Too bad we don't see this combination on any Mustangs in the states. The cross-ram design looked trick and made impressive power-always a good combination. Equipped with the Boss 290, the 5.4L produced 457 hp and 420 lb-ft of torque.

We ran into one difficulty with the Boss 290 test, namely a suitable throttle body. The Boss 290 intake was supplied by the great guys at Sullivan Performance, but the stock throttle body was nowhere to be found. To cure this problem, we clamped in place an aftermarket throttle body designed for an LS1, and were off and running. Vacuum readings in the manifold indicated that the LS1 throttle body did not represent a restriction at this power level. The cross-ram Boss 290 intake demonstrated its worth by producing 457 hp and 420 lb-ft of torque, bettering the Navigator intake from 4,500 rpm to 6,500 rpm. Even down as low as 4,000 rpm, the Boss 290 equaled the power output of the Navigator, though below that point, the torque production of long-runner Navigator clearly held the advantage.

The final intake to be run on the 5.4L was of the author's own design. This intake would not likely fit under a production Mustang hood, but the same could be said of some of the others. The tall deck height of the 5.4 combined with the intake height makes for a tall package. In truth, this was not one intake design but many, as the adjustable nature of the manifold allowed us to dial in the optimum runner length for this particular application. Though it was possible to improve both low and high-speed power production, this combination provided the best overall powerband. Running dual plenums joined at the rear with a 3.5-inch crossover tube, dual 75mm throttle bodies, and full-radiused air horns inside each plenum, the custom intake offered 456 hp and 433 lb-ft of torque. This combination bettered the power output of the Navigator intake from 3,600 rpm to 6,500 rpm but lost out from 3,000 rpm to 3,600 rpm. It should be obvious from the supplied power graphs (peak numbers tell only a small portion of the story) that the right intake can make a major change in the shape of the power curve. The trick is to dial in the effective operating range and install a manifold that will run well in that rpm band.