Big Game
Pro Dyno pumps up John Antunes’ Shelby GT500 with a big-bore 6.2
By Steve Turner
Photos courtesy of Pro Dyno
If you weren’t a Mustang enthusiast, you might assume that a Shelby GT500 with a supercharged 5.4-liter engine would provide more than enough propulsion. We know better. A stock GT500 is fun. A modded GT500 is a blast. However, while most people are happy with bolt-on enhancements and tuning, others want something a bit more aggressive. John Antunes falls into the latter category.
“…I wanted to have one of the fastest street GT500s,” John said.
To bring that plan to fruition, he turned to the skilled crew at Pro Dyno in Fort Mill, South Carolina.
“He came to us a few years ago to build his Boss 302 Laguna Seca; it ended up with a built Coyote with a (ProCharger) D-1 on it. He was more than ecstatic with how that build turned out so we entrusted us with his Shelby build that he had in mind,” Pro Dyno said. “This build has been ongoing for almost two years now. John wanted nothing but the best for this build, with nothing left untouched. A lot of time, money, attention to detail, blood, sweat and tears went into this build for John, to make sure he got the build he would be more than happy with!”
The original plan called for creating a big-bore engine for his 2008 Shelby GT500 base on an 2011-2012 5.4 aluminum block. However, when it was discovered that those blocks were out of production, they turned to one of the vaunted Trinity 5.8-liter blocks as the foundation for this big-bore beast. However, that plan presented its own challenges.
“…We had to upgrade to the 5.8 block, which in the end turned out to be a much better way to go,” Pro Dyno added. “The entire motor is all ’13-’14 components, so we had to piece together the entire motor. Every bolt and nut we had to buy separate because we did not have a donor motor, so tracking down each part was difficult.”
Like any thing worth waiting for, the results turned into something quite impressive. The 5.8 block allowed the Pro Dyno crew to really push the displacement envelope with a set of Darton Sleeves. In the end, they created a whopping 6.2-liter engine. They couldn’t top that with just any supercharger, so they crowed the 381ci engine with one of Whipple’s massive 4.5-liter twin-screw blowers.
The resulting combo assaulted the rollers on Pro Dyno’s in-house Dynojet chassis dyno with an output of nearly 1,200 horsepower and over 1,000 lb-ft of torque. That is enough to impress just about any enthusiast, but John has an especially high standard thanks to his personal collection of high-performance rides. Watch it run right here…
[video=youtube;4Yiw4RtoflU]https://www.youtube.com/watch?v=4Yiw4RtoflU[/video]
“I have a few fast cars, turbo Porsches, Ferrari, and a Ford GT, but none of them are as fast as this car!” John enthused.
Just because it’s fast doesn’t mean it’s finished, however. He plans to round his GT500 with gear that will better support its newfound steam.
“I’m going to upgrade the suspension for the new horsepower levels and traction issues that may be present in current form,” John added. “I have a friend that owns funny cars that is going to build the suspension for it. The car is currently set up for the previous 715 rear-wheel horsepower. After that I will be driving the car on the street and at the track.”
For now, however, you can keep reading to see the highlights of how Pro Dyno built the car up to four-digit power.
Rather than pulling the stock engine, Pro Dyno built a fresh engine for John Antunes 2008 Shelby GT500. That meant John could keep enjoying his ride until they installed the 381-cube powerplant.
While they had planned to start with an aluminum 5.4 block, those were out of production. As such, Pro Dyno opted for a Trinity 5.8 aluminum block and machined it to accept a set of Darton Sleeves.
Like a glove… The custom CP pistons fit the 3.70-inch bore provided by the Darton Sleeve-equipped Trinity block.
Pro Dyno spec’d out a set of custom Carrillo Billet Pro H-beam rods that deliver a stroke of 4.415 inches.
It took over a year to receive it, but the custom Sonny Bryant billet crankshaft is the heart of this combination.
Swinging on the billet Carrillo H-beams are a set of custom CP Pistons retained by H13 pins.
With a 3.70-inch bore and a 4.415-inch stroke, John’s new combo yields a whopping 6.2-liters of displacement.
To feed the big-bore short-block, Pro Dyno ordered a set of CNC-ported Trinity heads from Livernois Motorsports. These heads receive the full treatment, including a five-angle valve job, and a complete Livernois valvetrain.
Don’t let the looks fool you. Underneath those paint-matched timing gear is some impressive hardware. The cam covers shroud a set of Bullitt Race Cams custom blower grinds, which are spun via rugged Terminator Cobra timing chains and sprockets.
Harnessing the output of this earth-shaking combo is one of McLeod Racing’s GT500 Street twin-disc clutches, which are rated to handle up to 1,400 horsepower.
A big engine needs a big blower, and it doesn’t get much bigger than Whipple Superchargers’ 4.5-liter twin-screw supercharger. It’s good for up to 30 pounds of boost. This combo is fed by one of Fore Innovations’ Level 4 GT500 fuel systems and a set of Injector Dynamics ID2000 injectors.
With 6.2-liters of engine and 4.5 liters of supercharger, John’s GT500 needs to breathe. To make sure the exhaust wasn’t a restriction, Pro Dyno added a set of Kooks Custom Headers’ Cobra Jet race headers paired with the company’s 3.5-inch X-pipe.
Spun by an ATI 15-percent overdriven damper, the new Whipple 4.5 shouldn’t have a problem providing plenty of boost. With the engine and blower installed, there are just a few things to clean up before this jumbo combo is ready to roll on the Pro Dyno Dynojet with main man Dan Desio dialing in the tune.
With the massive, 4.5-liter Whipple cranking out 26 pound of boost, John’s 381ci GT500 put down 1,199 horsepower and 1,056 lb-ft of torque at the rear wheels, but we’'ll round it up and say it’s 1,200 horsepower. Either way it’s awesome.
