For 1964 significant engineering changes occurred, while the model lineup and styling remained relatively unchanged. The engine displacement was increased from 145 to 164 cu in (2.3 to 2.7 L) due to an increase in stroke; the base engine power increased from 80 to 95 hp (60 to 70 kW), and the high performance engine increased from 95 to 110 hp (70 to 80 kW). The Spyder engine rating remained at 150 hp (112 kW) despite the displacement increase of the engine. 1964 saw an improvement in the car's swing axle rear suspension with the addition of a transverse leaf spring along with softer rear coil springs designed to diminish rear roll stiffness and foster more neutral handling attributes. Spring rates could now be softer at both ends of the car compared to previous models. The heavy duty suspension was no longer optional, although all models now had a front anti-roll bar as standard. Brakes were improved with finned rear drums. The remaining pickup, the Rampside, was discontinued at the end of the model year.
Source: Wikipedia, 2012