Dad had a 74 \6 Duster and I had a 70 \6 duster, as well as a 65 \6 Valiant, but the Valiant was a 3 speed manual. Got 29 with the Valiant at 17 years old. Got 28 with the 70 and dad consistently got 30 with his 74. That's to an Imperial gallon. That would convert to 23-25 for a US gallon.