* 3.8L V6: This was a very common engine for the Delta 88 Royale in 1984.
* 5.0L V8: A larger V8 was also available as an option.
To know the exact engine size in a *specific* 1984 Oldsmobile Delta 88 Royale, you'd need to check the vehicle's identification plate (usually located in the engine compartment or on the driver's side doorjamb). The engine size will be listed there.