Shown is the redesigned cobra-head-shaped downpipe on the second-generation 6.7-liter Power Stroke. The shape is slightly more dramatic to accommodate the larger turbo on the updated diesel.

Engineers rarely pay attention to exhaust gases after they exit a diesel’s turbocharger. Just provide a direct path to the aftertreatment and exhaust systems that’s cost efficient and quiet was the usual direction.

Note the location of the turbo and the somewhat smaller cobra-head downpipe on this photo of a first-generation Power Stroke.

Advancement in CFD (computational fluid dynamics) computer modeling, however, is giving engineers more opportunities to open up horsepower and boost torque in addition to chasing those fumes out the tailpipe. Sharp-eyed observers have noted a distinctive “cobra head” shaped downpipe coming from the turbo on the second-generation 6.7-liter Ford Power Stroke engine. The new design was needed when Ford went with a larger turbo on the new engine. While it looks somewhat like an expansion chamber on a 2-stroke engine, the strategy is focused on getting the air out efficiently rather than tuning the exhaust pulses.

“Fluid dynamics allowed us to precisely tune the curvature and width of the pipe to optimize exhaust gas flow,” says Robert Wade, engine air path technical leader, adding that hundreds of hours were logged in simulation analysis to finalize the design. “It turns out that a downpipe shaped like a cobra head is the ideal design for air flow and breathability, which we validated through thousands of miles of durability testing.”

Basic principles of physics demonstrate that a turn or kink in the airflow path will disrupt that flow, thereby increasing pumping losses and forcing the engine to work harder to reach a power target. Ford says the cobra-shaped design acts like “widened, banked turn” and allows the spent gasses to flow smoother through the 90-degree turn and down to the aftertreatment system.

This abrupt 90-degree turn, of course, is necessary due to the “hot-V” location of the turbocharger between the cylinder heads. Ford bolts the turbo directly to the CGI cylinder block to improve packaging and get the exhaust heat to the turbo as quick as possible for improved response. This location also helps reduce noise. The intake charge, then, enters the aluminum cylinder heads from the outside, creating a reverse-flow layout.

The Power Stroke is currently rated at 440 horsepower with 860 lb-ft peak torque.