While we generally start off with a bone-stock motor and seek ways to improve upon the stock power output, this "Mods for 5.4 Mods" started out with something altogether more radical. This 5.4 Four-Valve motor from Sean Hyland Motorsports was anything but stock, and would serve well as a workhorse to run a number of tests. The first test involved the installation of the Vortech YSI supercharger originally intended for the top-speed shootout. Before adding the blower, the newly built 5.4 Four-Valve motor was broken in and run in normally aspirated trim. It produced 434 hp at 6,500 rpm and 387 lb-ft of torque at 5,200 rpm before the Vortech was added. I have to apologize to Vortech here as I feel that I let them down by configuring the 5.4 with nothing more than a six-rib blower drive. I was not able to locate a suitable eight-rib belt in the size required by the drive assembly and, instead of reconfiguring the drive (which required a great deal of fabrication), I went ahead and ran the motor hoping the six-rib was up to the task, at least enough to finish a couple of high-boost runs. It wasn't.
The six-rib drive system ultimately prevented us from reaching those huge power numbers, but it allowed us to see some big power numbers and even learn the effects of large-tube headers and ice water in the air-to-water intercooler. Using a custom tensioner, the six-rib serpentine system (coated with sticky track bite) provided sufficient tension to produce a repeatable boost and power curve to roughly 6,200 rpm. Beyond that, the belt slipped and the power plummeted. Equipped with the new Vortech YSI reverse-rotation blower, the 5.4 produced 843 hp and 689 lb-ft of torque at just over 15 psi. For our needs, the motor produced 799 hp at 6,100 rpm using a set of 1 5/8-inch Hooker street headers.
Suspecting the small headers might be limiting the power output, we installed a set of 1 7/8- to 2 1/8-inch race headers supplied by Accufab's John Mihovetz. Used on his old supercharged race car, the headers were large for most street applications, but since the power output had already exceeded 800 hp, we suspected the motor might benefit from additional exhaust flow. The headers were worth additional power, raising the peak power at 6,100 rpm to 823 hp, though the headers were worth as much as 35 hp at 5,600 rpm. Obviously, an 800hp motor will require something larger than your typical 1 5/8-inch street header, but good luck making a set fit in a 4V Cobra, especially one with a 5.4 engine swap.
The final modification on the list involved replacing the dyno water running through the Spearco air-to-water intercooler with ice water. The dyno water was actually hotter than ambient air by 15 degrees, so we knew additional charge cooling was available with ice water. We had planned to run ice water during the top-speed event and wanted to know if the modification was worth additional power, or was it just being used as a hedge against detonation? The ice water was run through the Spearco core using an electric pump and dedicated reservoir. Running 32-degree water through the intercooler was worth additional power, raising our peak number at 6,100 rpm to 852 hp. The gains offered by the ice water were as high as 35 hp at 5,900 rpm, so obviously it is a good idea to run ice water at the dragstrip or for a top-speed event where the transfer medium can be kept cold for the length of the full-throttle run. Naturally, this cannot be employed effectively on the street, as the ice in the water will eventually melt and heat up, lessening its effectiveness. We have more "Mods for 5.4 Mods" in store, including a Two-Valve Lightning buildup, the transformation of our current SHM motor into a Cobra R clone, and the installation of a pair of turbos. Mods gone wild indeed.
After running the motor in normally aspirated trim, we drained the conventional oil and replaced it with 5W-30 synthetic oil from Lucas. | 
Vortech supplied a reverse-rotation YSI supercharger for our test. The impressive impeller used on the YSI was capable of delivering over 1,200 hp, but, unfortunately, not with just a six-rib drive system. | 
Vortech also supplied a number of different blower pulleys for this motor, but we chose to start with the largest 3.00-inch pulley. |
On the dyno, we ran this Spearco dual-core air-to-water intercooler using the dyno water as the transfer medium. | 
The ysi blower produced just over 15 psi and pushed the peak power to 843 hp. | 
Since Vortech did not have a dedicated blower kit for the 5.4 Four-Valve application, it was up to us to find a drive system for the new blower. |
Replacing the 1 5/8-inch street headers with larger 1 7/8-inch headers improved output by as much as 35 hp. | 
Running ice water through the intercooler instead of dyno water improved the power output by another 30-35 hp. It's too bad the wimpy drive system fabricated by the author didn't allow us to rev the motor beyond 6,200 rpm, because this 5.4 was well on its way to exceeding 900 hp. | |