Richard Holdener
November 1, 2006
Who else would you want working on your mod-motored Ford GT than the wizard himself, John Mihovetz?

Things are good for your author, since I was recently lucky enough to be invited to a standing-mile acceleration test put on by our sister magazine, Motor Trend. That ranks high on the cool scale, especially given my affinity for all things related to top speed. Leave the drag racing to Smitty and Galimi-I prefer road racing, and even trips to Bonneville and El Mirage. This standing-mile acceleration test slots in there nicely, too.

As if the top-speed event wasn't enough, I also had a kind Ford GT owner use his car for the test. Imagine, a Ford GT owner willing to let us crank up the boost and timing, and fiddle with all the intricate items in the motor in order to make what is arguably the fastest vehicle ever to come with a Blue Oval even faster. Heck, the stock GT has been clocked at over 210 mph (sans limiter).

Preparation for the event allowed yours truly to gather much needed data for MM&FF's ongoing "Mods for Mods" series. Obviously, no such series would be complete without information on the ultimate modular motor, the Ford GT version.

The 5.4L Four-Valve combination stuffed into the rear (actually middle) of the low-slung Ford GT supercar combines all the torque-enhancing displacement of the supercharged Two-Valve Lightning motor with the free-breathing four-valve heads of the '03-'04 Cobra. In fact, this Ford GT motor does those systems one better by selecting not just any old supercharger, cylinder heads, short-block or oiling system. The 5.4 block used in the GT is specific to that application and features aluminum construction and dry-sump oiling. This means the block cannot be retrofitted for use in a Mustang chassis without taking the machining steps necessary to provide for the starter and wet-sump oiling system.

After spending several hours getting the low-slung Ford GT on the chassis dyno, the stock supercharged 5.4 pumped out 562 hp and 503 lb-ft of torque.

While the 5.4 Lightning and '03-'04 Cobra motors made do with the Eaton roots super-charger, the Ford GT is boosted by a 2.3L twin-screw supercharger. Considerably more efficient than the Eaton Roots blower used on the Lightning and Cobra applications, the twin-screw design provides the flow potential (and efficiency levels) required for supercar power levels at a reasonable boost pressure. Gains of 50-100 hp are available with just a pulley swap. Making that pulley swap happen is a bit more complex than yanking off the old one and installing a new one, but Kenne Bell has seen to make that exact scenario a reality for the handful of lucky GT owners.

We mentioned previously that the 5.4 is blessed with four-valve heads to maximize the breathing potential. While the '03-'04 Cobra heads would certainly offer flow and power gains over the two-valve PI heads used on the Lightning, the Ford GT engineers reached all the way up to the top shelf for headgear for their supercar.

Far and away the best set of factory cylinder heads for the modular motor came on the '00 Cobra R. The R heads featured revised port locations that offered tremendous gains over the standard offerings. Nestled between the impressive cylinder heads and 2.3L twin-screw supercharger was a dedicated intake casting and improved air-to-water intercooler. Rather than rely on the effective air-to-water intercooler system on the '03-'04 Cobra motor, the GT engineers stepped up things once again and designed a larger, more efficient intercooler system for the 5.4. Like the Lightning and Cobra intercoolers, the system used on the GT will easily support (and effectively cool) elevated boost levels.

Extensive cooling studies and powertrain development went into the GT project, the results of which were a motor capable of supporting a great deal more power than the rated output of 550 hp. We are proud to say that, like the '03-'04 Cobra before it, the power output of the Ford GT is significantly underrated. We measured near 550 hp (and 500 lb-ft of torque) at the wheels in bone-stock condition. No wonder this car will kick the living crap out of a Corvette.

The secret to the impressive power production is this supercharged Four-Valve 5.4 mod motor. This powerful DOHC motor can push the stock Ford GT to over 200 mph in stock trim.

Technical details abound for the Ford GT, but this episode of "Mods for Ford GT Mods" covers the ease at which we improved the power output of the already powerful supercharged 5.4L motor. Obviously, the first thing we needed to do was establish a baseline. Since the testing was performed at Kenne Bell, we hooked up all manner of data-logging equipment in order to take an in-depth look at the important variables that affect the generation of the power curve. Naturally, the torque, horsepower, and air/fuel curves are provided by the Dynojet, but for our needs, we also took a look at the timing curve, air temps (in and out of the blower), and even injector pulse width. Basically, we had all the data necessary to determine not just that we improved the power output, but (every bit as important) why a specific power gain occurred. The data would also be helpful in sourcing potential problems, but as luck would have it, none developed during testing.

Running the car in as-delivered condition, the impressive supercharged Four-Valve pumped out 562 hp and 503 lb-ft of torque at a maximum boost pressure of 11.7 psi. The wavy curve made it difficult to pinpoint the exact power peak, but know that this motor is rated at 550 flywheel horsepower and manages at least that much at the wheels in stock trim. As we have come to expect of these supercharged mod motors, the twin-screw-enhanced 5.4 offered a broad, flat torque curve. The motor exceeded 440 lb-ft of torque at the wheels as low as 2,000 rpm and hovered near 500 lb-ft for a solid 1,000 rpm. Even out at the factory rev limiter of 6,600 rpm, the torque curve was still showing 445 lb-ft. From the looks of the curve, we suspected the power curve was still on the rise as the engine encountered the 6,600-rpm rev limiter. Since the guys at Kenne Bell were set up with SCT software, we had the ability to raise the factory rev limiter. This modification would come after we increased the boost pressure via a brand-new billet blower-drive assembly from Kenne Bell. Since both the air/fuel and timing curves were conservative from the factory, we felt confident in cranking up the boost a few pounds.

Here is a shot of the factory blower snout compared to the new billet-aluminum version offered by Kenne Bell. Note that the factory snout featured a press-fit blower-definitely not designed with ease of replacement in mind.

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.