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.