On the dyno, the normally...
On the dyno, the normally aspirated 5.4L produced 441 hp and 387 lb-ft of torque.
The final touch on the 5.4L was the induction system. Though the motor was run in normally aspirated trim with a set of Hooker headers, the crowning touch on this combination was a Sullivan 5.4L intake manifold. Naturally, a stock Navigator intake was not going to get things done, so we stepped up to the Sullivan piece to further improve the breathing potential. In addition to the additional airflow offered by the Sullivan intake, the short-runner design (compared to most production intakes) enhanced power production higher in the rev range. While we had no intention of running this motor to 8,000 rpm, or even 7,000 rpm, we knew peak power would occur somewhere north of 6,000. Since we were looking for a four-digit peak power number, the short-runner Sullivan unit was just what the doctor ordered. To ensure adequate breathing throughout, we installed a 90-degree elbow from Coast High Performance, along with a 90mm throttle body from Accufab. The combination offered impressive breathing potential, especially once under boost. The final touch was the Sullivan fuel rails feeding the 65-pound injectors from Holley. As it turned out, even the 65-pound Holley injectors were insufficient to feed this thirsty mod motor once we installed the turbos.
The HP kit included a set...
The HP kit included a set of 67mm turbos capable of supporting over 1,200 hp, more than enough flow to meet our needs.
With the naturally aspirated combo finalized, it was time to talk turbos. We went right to the experts at HP Performance in Roswell, New Mexico. We suspect alien technology from the Roswell landing in the '50s, but whatever the reason, those guys know how to make boosted power. We relied on a twin-turbo kit designed for the 4.6L Cobra. HP is currently working on an upgrade kit for the Shelby motor, but our testing came before completion of that project. Besides, our 5.4L wasn't exactly a GT500 motor anyway. The twin-turbo kit featured a pair of 67mm turbos, complete with 0.70 A/R compressor housings and Stage 5 turbine housings with 0.63 A/R ratios. The combination offered an exceptional response rate and ultimate power potential. In fact, we suspect the 1,000hp mark was obtainable even with smaller 57mm turbos, but it's always nice to have more than you need, right? The kit also featured a front-mounted air-to-air intercooler, which we employed on the dyno using a dedicated cooling fan. The only change to what would be in the car was shorten-ing the tubing running from the exhaust manifolds to the turbos and to run the motor with a FAST management system.
The first step toward big power was to break in the new 5.4L combination. The normally aspirated motor was run with Lucas conventional oil and lightly loaded for 25-30 minutes before attempting any full-throttle runs. After the break-in procedure, the motor was tuned by Big Ernie Mena at Westech, and run in anger to the tune of 441 hp and 387 lb-ft of torque. Torque production from the 5.4L exceeded 375 lb-ft from 4,300 rpm to 6,100 rpm, making for one impressive powerband. After break-in, we installed the HP twin-turbo kit. The turbo system was run with pump gas up to 9 psi. At this point, we filled the tank with Rockett Brand race fuel just to be on the safe side. Given the boost and timing level required to reach our goal of 1,000 hp, we'd like to revisit the motor with larger injectors and pump gas. After tuning the different boost levels (in 2-psi increments), we finally reached 17 psi.
It was at this boost level that the 65-pound Holley injectors went static (at 6,000 rpm), but a fuel-pressure adjustment gave us just enough fuel for the twin turbo 5.4L to produce 1,002 hp at 6,500 rpm and 832 lb-ft at 5,500 rpm. With over 800 lb-ft available from 4,600 rpm to 6,500 rpm, this is truly a mod motor maxout.

The hot (turbine) side of...

The hot (turbine) side of the turbos featured Stage 5 wheels and 0.63 A/R ratios.

Boost pressure was fed through...

Boost pressure was fed through an efficient air-to-air intercooler before being forced into the awaiting 5.4L.

The only change to the twin-turbo...

The only change to the twin-turbo kit supplied by HP Performance was to shorten the tube connecting the tubular (and Jet Hot-coated) exhaust manifold and the turbo. This was done to facilitate mounting the system on the dyno and had no effect on the performance.

The kit was supplied with...

The kit was supplied with a pair of Tial wastegates to provide absolute control over the boost. The waste-gates were equipped with long (red) wastegate springs, which produced a minimum of just over 7 psi on this combination. Boost was further adjusted using a Turbo XS manual wastegate controller.

This shot illustrates the...

This shot illustrates the oil feed to the turbo and return line back to the oil pan. It was necessary to weld 11/42-inch tubing onto the factory oil pan to serve as oil drains.

Normally Aspirated 5.4L Four-ValveThe...

Normally Aspirated 5.4L Four-ValveThe combination of the SHM 5.4L short-block, ported Navigator heads, and Stage 2 cams produced an impressive normally aspirated combination. The Sullivan intake was on hand to allow the motor to produce effective power past 6,000 rpm. So equipped, the 5.4L produced 441 hp at 6,500 rpm and 387 lb-ft of torque at 4,900 rpm. Despite the rather low static compression (this is a turbo motor), torque production exceeded 375 lb-ft from 4,300 rpm to 6,100 rpm. What we had was an efficient normally aspirated motor just begging for boost.

Twin-Turbo 5.4L Four-Valve...

Twin-Turbo 5.4L Four-Valve (17 psi)Our guess is the first thing people will notice about this power curve is that horsepower was still climbing rather rapidly at our shut-off point of 6,500 rpm. Had we not run out of available injector, both the HP twin-turbo system and the 5.4L had plenty more to offer. Still, any motor that pumps out 1,002 hp and 832 lb-ft of torque is plenty potent. Every bit as impressive as the peak power numbers was that they came at just a hair over 17 psi. Credit for the big power at a low boost level goes to the effort made to produce an efficient normally aspirated package along with the impressive twin-turbo system from HP Performance. The twin 67mm turbos offered full boost as low as 3,500 rpm (the lowest tested with the turbo combination) along with the ability to easily surpass 1,200 hp.

Since the 5.4L was not run...

Since the 5.4L was not run with the factory manage-ment system, we replaced the MAF assembly with a revised section of inlet tubing from the intercooler to the throttle body.

A dedicated intercooler fan...

A dedicated intercooler fan was positioned directly in front of (closer than in photo) the air-to-air intercooler.