Responding to complaints about the aircraft's handling qualities, Piper introduced the PA-34-200T Seneca II. The aircraft was certified on July 18, 1974 and introduced as a 1975 model.
The new model incorporated changes to the aircraft's control surfaces, including enlarged and balanced ailerons, the addition of a rudder anti-servo tab, and a stabilator bobweight.
The "T" in the new model designation reflected a change to turbocharged, six cylinder Continental TSIO-360E or EB engines for improved performance, particularly at higher altitudes. The Seneca II retained the counter-rotating engine arrangement of the earlier Seneca I.
The Seneca II also introduced optional "club seating" whereby the two center-row seats face rearwards and the two back seats face forward allowing more legroom in the passenger cabin. A total of 2,588 Seneca IIs were built.
Gross weights are 4,570 lb (2,070 kg) for takeoff and 4,342 lb (1,969 kg) for landing, with all weight in excess of 4,000 lb (1,800 kg) required to be fuel.