The GM or "Detroit Diesel" two-stroke diesel engines have a power stroke every time the piston goes down, were most engine most folks know of are four-stroke, meaning there is only one power stroke for every two times the piston is moving down.
So with this in mind, a 4-71 would make power with all four cylinders for every rotation of the crankshaft, while the stock 6 cylinder would only have power from three of it's six cylinder on each rotation of the crank. the crank in the 6 cylinder has to turn twice to fire all 6 cylinders, while the 4-71 would have fired all 4 cylinder twice in two rotations of the crank, meaning you got power from 8 cylinders or two more than the 6 cylinder.
The 4-71 Diesel should have a higher torque rating than the stock 6 cylinder, but it may not have the horsepower. Diesel engines are built for pulling power (torque), while gas engines are built for speed (horsepower).
