The largest engine option in the 1970 Chevrolet Chevelle SS was the 454 V8.
For 1970, Chevrolet expanded the Chevelle SS engine lineup with the 454-cubic-inch big-block V8. It was available through the SS equipment option and came in LS5 and LS6 forms. The LS5 was the milder version, while the high-compression LS6 used a solid-lifter camshaft and was advertised at 450 gross horsepower, making it one of the era's most famous muscle-car engines.
The 454 replaced the previous 396-based top performance choice in Chevrolet's lineup, although the 1970 SS 396 designation remained. That label can confuse readers because the so-called 396 engine was actually a 402-cubic-inch version by 1970, still marketed under the familiar name.
The 427 V8 was not the regular largest engine option for the 1970 Chevelle SS. Chevrolet instead used the 454, with cowl induction available on appropriate versions. The LS6 was extremely potent, but relatively few were produced: 4,475 LS6 Chevelles are recorded for 1970.