Avanti engines were developed from the basic Studebaker V-8. The R1 was a 289 cubic inch carbureted version with a 4 barrel and the R2 was a 289 cubic inch version equipped with a supercharger. Most Avantis were equipped with one of these two engines, though the R2 could not be equipped with air conditioning. The R3 was a special performance supercharged variation displacing 304 cubic inches and very few of these were built. The R3 version came with a bored out 304.5 cubic inch V-8 stuffed into the engine bay, modified suspension and the standard front disc brakes. Engine development was the responsibility of Andy Granatelli.

Like the earlier 289 cid R2 version, the R3 was also supercharged, fully blueprinted to racing specs and hand built by Paxton. American auto magazine, Road & Track, tested an auto-equipped R3 back in 1963 and recorded a zero to 60 mph (100 km/h) time of 5.5 seconds!

There were also R4 and R5 performance variatrions, but none of these were sold to the public. In 1963 and 1964, Larks and Hawks could be ordered with Avanti engines, and a relatively small number were so equipped. As would be expected, parts for R series engines are harder to find and more expensive than for standard Studebaker V-8's.