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.