A big-block engine is a North American V8 in a family of engines which generally have greater than 5.9 litres (360 cubic inches) of displacement; factory engine sizes reached a peak of 8.2 litres (500 cubic inches) in Cadillac's 1970s range. Smaller V8 engines are known as small-blocks; some members of small-block engine families may exceed 6 litres, blurring the distinction somewhat. The distinction came about in the early 1960s when the large full-size cars needed a bigger V8 than the smaller intermediate and compact cars. Prior to that point, manufacturers normally had only one V8 engine line.

The term is normally used only for engines from the "Big Three" (Ford Motor Company, General Motors, and Chrysler Corporation) since the other companies did not keep two V8 engine size families.

Big-block V8s were most commonly used in full-size and luxury cars, rather than performance vehicles. Thus, they were commonly tuned and built for smoothness, low-end torque to get heavy cars rolling, and effortless cruising. Many big-block engines were less technically sophisticated than their small-block counterparts, and their power-to-weight ratios were often lower.

They did see performance applications, however. Performance-tuned big-blocks were used in NASCAR racing, and homologation requirements saw these engines sold for road use. NASCAR's 7-litre engine size limit explains why many high-performance big blocks are of this size; Chevrolet's 427, Ford's 427, Chrysler's 426 Hemi. In the mid to late 1960s, the explosion of the muscle car market saw performance big-blocks fitted to intermediate-size cars. Some used derivatives of the racing engines, but in addition performance versions of former luxury motors were produced.

After the 1973 oil crisis, the days of the big-block in passenger cars were numbered. By the end of the 1970s, they were no longer to be found. However, these engines remained in use in pickup trucks and other non-car uses.

Ford

• Ford FE engine
• Ford 385 engine

General Motors

• Chevrolet Big-Block engine
• Cadillac V8 engine

Chrysler

• Chrysler B engine
• Chrysler RB engine
• Chrysler Hemi engine