and high-performance applications because they have no problems with their connecting rods breaking; unlike other domestic automakers' large displacement small block engines. The Gen-2 AMX 390 produced and was built in 1968 and 1969. Gen-3 AMC tall-deck (1970–1991) In 1970, all three blocks grew in deck height and gained a new head design. Although the engine is an outgrowth of the Gen-2 V8, these changes cause it to be regarded as the third generation of AMC V8, or "Gen-3". The stroke and deck height on the 290 and 343 were increased by on both engines, becoming the and , respectively. The 1970 AMX 390 remained at the same displacement by using a special connecting rod and piston for this year only. It is believed that AMC kept the 390 this last year due to the reputation it had garnered in the two-seater AMX, then still in production. (It was discontinued after 1970). In 1971 the 390 was also stroked by the same as the other two versions of the engine to become the 401. The other change in 1970 was the switch to the "dog-leg" heads. These heads flow 20% better on the exhaust side than the 1966-1969 rectangular port heads and are thus the best for performance. There are two reasons for the flow increase: (1) the area of the port is larger, due to the dog leg and (2) the shape of the port floor was changed from a concave to a convex curve. The concave floor tended to bend the exhaust flow upwards which caused turbulence when the flow was forced to go down into the exhaust manifolds. By switching to a convex floor the curvature of the flow starts in the head and proceeds much more smoothly into the exhaust manifold resulting in less turbulence and better flow. The center two intake bolts on each head were relocated to prevent accidental mix-ups of Gen-2 and Gen-3 intakes. AMC heads 319 and 291 used between 1970-mid 1971 have the dog-leg exhaust ports and 50-52 cc combustion chambers. They are commonly identified by the first three (319) or last three (291 for the 360-401 heads; 304 used a different casting) digits of the casting number. There was a U.S. auto industry-wide shift to lower compression ratios in mid-1971, so AMC increased combustion chamber size to 58-59 cc. The first three digits of the casting number on the large