As for the 6.7L, turbo failure was common on ’11-’14 engines, the connecting rods are a known weak link (with 650 to 700rwhp being their generally accepted limit) and emissions system-related issues come and go. We’ve seen 700rwhp squeezed through the OEM turbochargers and the factory connecting rods capable of handling 900rwhp. However, in performance applications where big horsepower is the name of the game, the 6.4L is tough to beat. As far as its emissions system, fuel system and overall engine longevity is concerned, the 6.4L leaves a bit to be desired-and repairs can be extremely spendy. With nearly 12 years of seat time in the 6.4L and roughly nine years since the 6.7L’s debut, both power plants have been out long enough to draw a host of conclusions. For it, they upped the power numbers to 390hp and 735 lb-ft of torque from a deep-skirt, compacted graphite iron block that created 406 ci of displacement.
Ford fully took over the reins of the 6.7L Power Stroke, creating it in-house. The cast-iron block came from the factory putting out 350hp and 650 lb-ft of torque, with its 3.87-in bore and 4.13-in stroke creating 390 ci of displacement. The 6.4L Power Stroke was the third, and last, Navistar-built turbo-diesel engine for Ford. The all-new V8 introduced the pickup segment to a compacted graphite iron crankcase, reverse-flow cylinder heads, water-to-air intercooling and reached the 400hp and 800 lb-ft of torque thresholds before GM and Dodge could. On the other hand, Ford’s 6.7L Power Stroke was a ground-up undertaking from FoMoCo that practically reinvented the wheel in light-duty diesel enginery. Thanks to its high volume Siemens common-rail fuel system and factory-installed compound turbocharger arrangement, the Navistar-built 6.4L was a great platform for making horsepower, but it shared much of its architecture with the 6.0L that preceded it. There might not be a better way to illustrate polar opposites within the same engine lineage than by comparing the 6.4L Power Stroke with the 6.7L Power Stroke. 6.4L vs 6.7L: Which Power Stroke is Really Better?