After we discovered Sean Porter of ATS Diesel had spent an inordinate amount of time and money on a '99 Ford F-350 called Great White, we were eager to see what he was up to these days. For the second part of his tale, the big fish is similar, but this time it's an '08 F-350 with a twin turbo 6.4L Power Stroke under the hood. We met up with Sean just before the annual ATS Diesels on the Mountain event (featured in our March '09 issue) to see how the new project was progressing.
Obviously, the new 6.4L engine is way more complicated than his 7.3L, but it's cleaner and quieter. And, instead of a single turbo that Ford used on previous Power Strokes, the main component of this system is a smaller, fixed-vane turbo providing constant boost to a bigger variable geometry turbo. The twin-turbo system is designed to provide better throttle response while in motion, but ATS has gone even further with its aftermarket upgrades for the 6.4L.
As on the previous Great White, Sean raided the ATS parts bin for an Aurora 5000 turbo and E-Power programmer. It's critical to have the two working together, since simply pressurizing the cylinders with more boost doesn't do any good without precise fuel and airflow. That's where the E-Power programmer comes in, which requires new software for the newer engine, with fuel maps for as many as 10 different settings. Sean is still playing around with five of them in particular, which increase the power gradually from 60 hp to 120 hp, along with competition and fuel economy settings.
Getting back to the hard parts, the stock high-pressure turbo remained stock for low-end acceleration, but the ATS Aurora 5000 fixed-vane turbo replaced the larger factory unit for even bigger gulps of air. If you look closely at the underhood photos, the engine bay looks fairly stock, except for the AFE intake and some extra sensor lines. That's because he outfitted the factory turbo housing with Aurora's compressor and turbine wheels. Before fitting them inside, he had to machine and chamfer the entire housing diameter about 40 to 60 thousandths, leaving about two thousandths of clearance between the blades and wall.
In contrast to the generic factory unit, the ATS fixed blades on the billet wheels are custom shaped for better efficiency and a bit more pitch. The initial flow of exhaust gas from the manifold has not been changed. Although, since the downpipe is still the stock 4-inch diameter, it connects to a 5-inch exhaust system via an adaptor.
For engineering purposes, Sean mounted six blue-tinted instruments above the rearview mirror. There is a gauge for each turbo to monitor drive pressure, along with a monitor for exhaust backpressure, boost pressure, and exhaust gas temperature. He's being extra careful on the power gains to avoid mistakes made in the past. Why so? The reason is fairly obvious: "It's called money. My theory is I'm gonna drive one of these trucks home in one piece. The new emissions equipment makes it much more of a challenge as well."
 A slew of Auto Meter gauges...  A slew of Auto Meter gauges surround the rearview mirror, where EGTs, boost from both turbos, and transmission temperature can be viewed with a quick glance. |  Aside from an AFE intake,...  Aside from an AFE intake, the engine compartment looks relatively stock. But the low-pressure turbo was outfitted with Aurora's new compressor and turbine wheels, which required reworking the factory housing diameters for proper clearance. |  The Gorilla exhaust stacks...  The Gorilla exhaust stacks from ATS route out behind the cab after flowing through one of ATS' new high-flow diesel particulate filters. According to ATS, its high-flow units improve exhaust flow by 30 percent. |