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.