What was the top engine option for the 1970 AMC AMX?

The top engine option for the 1970 AMC AMX was the 390 cubic inch V8.

American Motors offered the AMX with a range of V8s, but the largest and most powerful available engine for 1970 was the 390-cubic-inch V8. It used a four-barrel carburetor and produced 325 horsepower, giving the compact two-seat AMX the muscle-car performance buyers expected.

The 1970 AMX received a substantial styling update, including a longer hood with a pronounced power blister, a full-width grille, and revised rear lighting. Its short 97-inch wheelbase and two-seat layout made it distinct from larger four-seat muscle cars, while the optional Go Package added performance-oriented equipment and was available with the 360 and 390 engines.

A frequent mix-up is the 401-cubic-inch V8, which became important in later AMC performance cars but was not the top AMX engine for 1970. The newly introduced 360 four-barrel was also available that year, but it sat below the 390 in the engine hierarchy. Thus, 390 cubic inch V8 is the canonical answer.