* 396 cubic inch (6.5L) big-block V8: This was a popular option and a key identifier of the SS. Several variations existed with differing horsepower ratings.
* 389 cubic inch (6.4L) big-block V8: Less common than the 396, but still possible.
* 283 cubic inch (4.6L) small-block V8: A smaller engine option that was also available.
* 327 cubic inch (5.4L) small-block V8: Another small-block V8 option. This was likely more common than the 283.
To know the *exact* engine in a specific 1966 Chevelle SS, you'd need to check the vehicle's documentation (build sheet if available, or the VIN plate).
