In 1964, Buick replaced the 215 with an iron-block engine of very similar architecture. The new "small block" engine had a bore of and a stroke of for a displacement of . It retained the aluminum cylinder heads, intake manifold, and accessories of the 215 for a dry weight of . The 300 was offered in two-barrel form, with 9.0:1 compression, making at 4600 rpm and at 2400 rpm, and four-barrel form, with 11.0:1 compression, making at 4800 rpm and at 3000 rpm.