Richard Holdener
January 2, 2014

The avenues for maximizing mod motor performance are many and varied, ranging from your basic bolt-ons to full-blown build-ups. We here at MM&FF enjoy a good air intake, throttle body, or after-cat test as much as the next guy, but this particular story is about going into full beast mode.

Beast mode is serious, by the way. How does 1,600 horsepower worth of beast sound? Once you discover the purveyors of the powerplant, the output should come as no surprise, but the method to our madness in no less impressive.

As fanatics of forced induction, we have come to expect big power from boosted Blue Ovals. One need only look at the factory ratings of some of the recent mod motors to understand our fascination. The Two-Valve Lightning, the Four-Valve Cobra, and now the 5.8L Shelby have clearly demonstrated how well the mod motors respond to boost.

Healthy in stock form, owners soon realized the factory output was just scratching the surface. Increased head flow, wilder cam timing, and (of course) more boost brings even more power.

Though cranking up the boost is a time-honored tradition among enthusiasts, there is obviously a limit to any combination, or is there? Sporting a Chevy-smashing 662 hp, the current 5.8L Shelby GT500 is one serious piece of hardware. Considerable chunks of power are just a blower pulley away.

Truth be told, the pulley swap requires additional tuning, but it is not uncommon to see three-digit power gains. Eventually, the factory supercharger with be the limiting factor, but swapping out the Roots blower for a twin-screw can yield dramatic results.

One need only look at the Shelby Super Snakes and GT1000 packages to see just how much power is available from a new mod motor equipped with a Kenne Bell supercharger. Not long ago, 1,000 horsepower was serious business, but the recipe for a 1,000hp Shelby motor has become somewhat common.

As impressive as these combinations are, The Beast has officially raised the bar on mod motor performance—a lot!

Not surprisingly, this monster mod motor came from the experts at Accufab Racing. With the title of World’s Most Powerful Mod Motor (comfortably over 2,000 hp from 281 inches), the gang at Accufab took what they learned from years of running their turbocharged 4.6L and applied it to a supercharged 5.4L.

The results are unofficially the most powerful supercharged 5.4L on the planet. They were hesitant about forking over some of the specs (like cam timing), but we’re offering up the remainder of information about what it takes to coax 1,600 hp from a blown cammer.

The project started by providing the necessary strength to withstand the tremendous cylinder pressure. The Ford GT aluminum block was deburred, precision machined, and prepped to receive a Bryant forged steel crank (stock stroke), custom Manley rods (built to Accufab specs) and a set of custom JE forged pistons. That the ultra-thick forgings were built to withstand the rigors of boost came as no surprise, but who expected combining 14.0:1 compression with 26 psi of boost?

Knowing that the best route to pressurized power was to maximize normally aspirated performance, Accufab rightfully chose the elevated static compression.

For your typical street motor, the combination of high compression and boost can be problematic. For this combination, the issues associated with high compression and boost were addressed with octane and intercooling.

First and foremost, the use of M1 methanol fuel added a safety margin that’s just not available on gas, even C16 race fuel. The methanol offered both a charge-cooling effect and elevated octane rating, but Accufab took the cooling one step further with the use of an ultra effective air-to-water intercooler system.

At the track, runs are made with ice water to maximize cooling, but all dyno testing was performed with ambient dyno (meaning more power was available). According to Accufab’s John Mihovetz, the combination of ice water and a slightly pressurize inlet system might yield as much as 50 additional horsepower. One additional factor that contributed to the ability of running both high compression and boost was the cam timing. You learn a great deal about mod motor cam timing after campaigning turbo and supercharged versions for more than a decade. While he would not provide the exact specs, Mihovetz points to the cam timing as one of the critical elements in the success of this monstrosity.

After years of figuring out how to seal up force fed Fords, Accufab took what it learned and applied it to the Kenne Bell supercharged 5.4L. Since boost alone wasn’t enough, the solid short-block received a number of upgrades that allowed it to properly process the airflow. Remember, power is a function of airflow into and out of the motor. Helping the airflow equation were ported heads, the aforementioned cams, and a dedicated induction system.

For this project, Accufab started with Ford GT heads, but the castings were treated to extensive porting, larger (38mm/32mm) valves, and even custom valveseats. Flow was important, but so too was the ability to withstand the harsh environment.

Sealing is paramount when the boost gauge swings up near 30 psi, so the GT heads were secured using lock-wired, copper head gaskets, and ARP 2000 head studs. The GT500 blower intake was chosen over the Ford GT version for its use of a single injector (Ford GT intake used dual injectors). As with all the components on this buildup, the intake was heavily massaged to maximize performance.

All the trick engine components in the world are useless on a blown motor unless you have the right supercharger. The need for an efficient, high-capacity supercharger lead Accufab right to the Kenne Bell 3.6L and 4.2L Twin Screws, both of which have been used successfully to exceed 1,600 hp.

As delivered from Kenne Bell for use on a GT500, the Kenne Bell supercharger upgrade kit utilized the factory air-to-water intercooler. Expecting this combination to double the power output of a typical modified GT500 mill, the experts at Accufab modified the air-to-water intercooler to increase the effectiveness. The combination of an 8-inch crank pulley, a 3.5-inch blower pulley, and an engine speed exceeding 8,000 rpm eventually produce peak boost levels of 26 psi.

Looking to minimize any airflow restrictions into the blower, Accufab whipped up a trick, dual-throttle body inlet designed to accept a pair of its massive 105mm throttle bodies. Wanting even more, they added a pair of radiused airhorns for good measure. The crowning touch was a dedicated Motec management system controlling 225-lb/hr injectors.

1. Replacing the stock blower with a Twin-Screw unit from Kenne Bell has the potential to take your Shelby into four-digit power levels.
2. The Beast from Accufab was tested with both the 3.6L and 4.2L blowers from Kenne Bell. Both units exceeded 1,600 hp.
3. The current Kenne Bell twin-screw supercharger is the result of extensive research and development, including work on its in-house blower dyno.
4. The new series of Kenne Bell blowers were available with liquid cooling designed to stabilize the temperature differential between the cool (inlet) and heated (discharge) sides of the blower casing.
5. Inlet restrictions are critical on positive displacement superchargers, so The Beast was fed by this fabricated Accufab intake featuring a pair of 105mm throttle bodies, complete with radiused air entries.
6. Massive power production required extensive work to the Ford GT heads. According to Accufab, the heads flowed a touch over 330 cfm on the intake and 280 cfm on the exhaust.
7. The work performed to the Ford GT head included a set of intake and exhaust valves measuring 38mm and 32mm, respectively.
8. No, he won’t divulge the specs, but Accufab was quick to credit the custom cam profiles for much of the power level.
9. Reliability and power were increased on the high-compression, supercharged 5.4L thanks to a dedicated dry-sump oiling system.
10. Custom coil packs were employed alongside the Motec management system to ensure precise tuning and plenty of spark energy.
11. Blower speed is a function of the engine speed multiplied by the pulley ratio. The Beast pumped out 26 psi of boost at 8,000 rpm thanks to the combination of an 8-inch crank and 3.50-inch blower pulleys.
12. Accufab tried a number of header combinations but eventually settled on a custom set of 2.0-2.125-inch step headers with 4.0-inch collectors.
13. With methanol flowing freely through the 225-lb/hr injectors, the supercharged mod motor pumped out an amazing 1,601 hp and 1,144 lb-ft of torque.
The first thing you notice about this graph are the huge power numbers, peaking at 1601 hp and 1,144 lb-ft of torque, but also note this 5.4L revved past 8,000 rpm. That is a lot of engine speed (and attending piston speed) considering the sizable stroke on the 5.4L.