The 318 is a member of the LA (Light A-series) small-block family that also produced the 273, 340, and 360. In 1970 it was the standard V8 on most Coronets, Belvederes, and Furys; standard on most pickups; and a no-cost option on cars where it was not standard. Two-barrel carburetor, 8.8:1 compression, period-rated 230 hp gross at 4,400 rpm and 320 lb-ft at 2,000 rpm.
Phil's question — what makes a 440 different from a 383, a 318, or the 305 in his Trans Am — has its plain answer here: the 318 is two cubic inches shy of half the 440's displacement, in the smaller small-block family rather than the big-block RB family, with a meaningful weight savings and a corresponding power deficit. It is not a muscle engine; it is the engine that made cars run for two hundred thousand miles on weekly fuel-ups.