Or search: gas, gun, auto, pedal, plane, valve, linac, enzyme, treadle, catalyst, collider, throttle, chemistry, automobile, biocatalyst
4 Syllables: SUUU
educator, elevator, generator, legislator, legislature, liberator, moderator, operator, procurator
5 Syllables: USUUU
collaborator, investigator, refrigerator

Found 12 words across 2 groupings. Skipped 5 excess words of a similar stem.