* 350 cubic inch small-block V8: This was a very popular choice and came in various horsepower ratings.
* 396 cubic inch big-block V8: Also available in different horsepower versions.
* 454 cubic inch big-block V8: The most powerful engine option available.
There wasn't a single "standard" engine for a 1970 Chevelle SS. To know for sure what engine *a specific* 1970 Chevelle SS has, you'd need to check the vehicle's documentation (like the original build sheet if it survives) or inspect the engine itself for identification numbers.
