Built from 1946 to 1947, the J1 was released as a two-seater competition car together with the K1 touring two-seater and the L- Type touring 4-seater. The J1 was a starkly trimmed and equipped 2-seater competition car on a wheelbase. Powered by a overhead valve Mercury V8, the J1 had a top speed of , limited by the low rear axle gearing. Only 12 were produced and went only to buyers who would rally them. They had good ground clearance and the front wings were removable. Copies driven by Allard himself, Maurice Wick, and others, and was a successful racer. Imhof won the 1947 Lisbon Rally in a J1 powered by a Marshall-supercharged version, while Leonard Potter took the "Coupe des Alpes" that year.