The R1 was the base Avanti engine. It displaced 289 cubic inches, and was rated at 240 HP. It was advertised as having a four barrel carburetor, 3/4 race cam, and other performance enhancements.

The term "3/4 race cam" is an old hot rodding term to describe a camshaft that had more lift and duration than a stock camshaft, and was still reasonably streetable.

Other Avanti engines were as follows: R2 was supercharged and created 290 HP; the R3 was also supercharged, and it was rated at 335 HP; an experimental R4 with dual quads making 280 HP, but it's not clear if it was ever sold to the public.

Finally, there is documentation that Studebaker had a 304 CI R5 engine, that had twin superchargers, fuel injection, and magneto ignition, producing 575(!) HP.

Reference to other Avanti engines are to be found; whether or not they were ever factory installed and sold to the public remains unclear.