Ford GT Motor Modifications - Mods For Ford GT Mods

Much like the factory Eaton Roots-style supercharger used on the Lightning and Cobra, the blower pulley on the 2.3 twin screw blower used on the 5.4 Ford GT motor was not set up for easy pulley swaps. Not surprisingly, Ford did not want to provide GT enthusiasts the ability to crank up the boost at will, at least not while the motor still enjoyed the full factory warranty. With the stock blower pulley a press fit, and the pulley dimensions relative to the snout size ultimately limiting the size of a smaller pulley, Kenne Bell decided the best way to approach the pulley dilemma was to change out the whole nose drive assembly.

Though Kenne Bell will have a complete blower upgrade capable of pushing the GT motor to stratospheric power levels, we took a look at the pulley upgrade system for this round of "Mods for Ford GT Mods." Since the motor was already equipped with a twin-screw blower, Kenne Bell designed a new nose drive assembly machined from billet aluminum and polished to a mirror finish. In fact, the new billet nose drive deserves a matching blower housing, as the polished Kenne Bell upgrade looked out of place on the satin twin-screw blower. Though constructed of polished billet aluminum, the real key to the new nose drive assembly was the ability to change blower pulleys at will. The stock blower pulley on this '05 GT measured 3.19 inches, though we have heard of different measurements on other GTs. The new Kenne Bell nose drive provided for pulley changes down to 2.50 inches, allowing GT owners to run nearly 20 psi of boost (though likely not on pump gas despite the super efficient factory intercooler).

Replacing the nose drive assembly required removal of the supercharger, but GT owners and tuners alike will be happy to know that blower removal took just a few minutes. Lifting the blower assembly out past the firewall braces required an extra pair of hands (we took great care when working on this car), but the removal required only a few retaining bolts, vacuum lines, and the factory corrugated air inlet tube. Then, Ken Christley from Kenne Bell drained the fluid and unbolted the factory nose drive. The new billet GT-HCD drive was installed using a new drive coupler.

After filling the new drive with the supplied gear oil, we were ready to install the blower assembly back on the 5.4. For this first test, the drive was set up with a 2.75-inch blower pulley, which resulted in a peak boost pressure of roughly 15 psi (we relied on the factory gauge). The increased boost pressure really made itself known by upping the peak power output of the GT motor from 562 hp to 615 hp. The peak torque also took a sizable jump, from 503 lb-ft to 555 lb-ft. While the peak power and torque gains are nice to brag about, the real gains in acceleration come from the fact that the power gains were present throughout the rev range. Acceleration is all about average torque production, and this is where positive displacement superchargers really shine.

While the power gains offered by the additional boost pressure were impressive (who can argue with 53 hp), we noticed several dips in the torque curve produced by the new blower pulley. Here is where data logging paid huge dividends. It told us the dip in power from 2,700 rpm to 3,500 rpm was due to excessive timing retard on the part of the ECU. Apparently, the factory computer (wisely) pulled timing down low when recognizing the higher boost pressure (seen by the map sensor and MAF). Knowing that additional torque gains were available in this rpm range and that additional peak power gains were available from the conservative timing and air/fuel curve, Christley took to the computer to tune in some more power. Not wanting to grenade a brand-new GT motor, we took the liberty of adding 109-octane unleaded race fuel to the tank to hedge our bets against detonation. Why the 5.4 motors were not equipped with knock sensors is anyone's guess, but if there's one motor from Ford that should have the precautionary safety devices, it is this super-charged GT powerplant.

The extra octane provided by the race fuel allowed Christley to get slightly more aggressive on the tune, adding timing and leaning out the mixture in an attempt to maximize the power output throughout the curve. The results were impressive, as the tune (using SCT software) unearthed as much as 100 extra lb-ft of torque at 3,300 rpm. The peak torque now stood at 604 lb-ft (a solid jump of 50 lb-ft from the untuned combination,) and the power peak was now up to 645 hp. With just a pulley change and tuning, we had managed to increase the power output of the 5.4 GT motor by nearly 100 hp and 100 lb-ft of torque.

While you might think the average GT owner would be happy with an additional 100 hp and 100 lb-ft of torque, we're not stopping here. In our next installment of "Mods for Ford GT Mods," look for exhaust modifications from Ford Racing, a revised throttle body and inlet from the flow fanatics at AccuFab, and possibly even more boost with a smaller blower pulley. Of course, we will have to revisit the tuning wizards at Kenne Bell to dial in the new combination, but we hope the GT motor continues to respond favorably to modifications. If all goes well, we hope to top the 700-rwhp mark without removing so much as a valve cover. We know that additional boost will bring the desired power, but we hope to find at least some power elsewhere.

Heck, even if we find no power in the induc-tion or exhaust, we get to work on a Ford GT. That alone is worth the hours spent on the dyno. Watching the changes in the dyno graph is just icing on the cake. We can tell you from first-hand experience that this car is easily a mid-10-second ride. We can't remember riding in a car that pulled this hard on the street, and we look to make it even faster.