These venerable in-line six-cylinder Detroit Diesels boast lineage that dates back some 50 years. The Series 71 engines were originally developed to power World War II Navy landing craft. And today, in evolved form, they can lay claim to being perhaps the most popular Detroils in pleasure-yacht applications, underscoring the soundness of the DDC concept of "evolutionary technology."

Like all DDCs, the 6-71s are wet-sleeved for efficient cylinder cooling, and their crankshaft main journals are dual-drilled for a 110-percent improvement in oil-film thickness, resulting in longer main-bearing life. They also incorporate water-cooled turbochargers innovative bypass blowers, two-pass aflercoolers, and waler-cooled exhaust manifolds.

Two-stroke cycle operation means each piston generates one power stroke for every two piston strokes. This means more horsepower, but at some penalty in efficiency. DDC has overcome much of that deficit with its by-pass blower and careful matching of turbochargers. These kinds of developments have allowed basically the same engine to go from just over 100 hp in its original form lo 485 hp today.

This review/article originally appeared in Power & Motoryacht Magazine, May 1993 and is written by Phil Friedman. For more great powerboat reviews, visit their website and subscribe at: