They had a lightweight, all-aluminum Lotus-sourced DOHC 16V two-liter four cylinder that put out something like 140bhp. The light motor gave it a 50/50 weight distribution for good handling, and the U.S. emissions-compliant version did 0-60 in 8.1 seconds.
This may not sound spectacular either by the standards of the muscle car era or today, but during the Malaise Years, when the 302 V8 in a Mustang Cobra II only had a hundred and thirty ponies, the Jensen-Healey was pretty sprightly. In fact, the next place this motor would turn up was in the early Lotus Esprits...