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The Pontiac Tempest's Smooth Ride
Though the engine was in place, the Pontiac Tempest faced some additional challenges. With competitive power levels, low development cost, and the wide range of commonality with the 389 V-8, the slant-four program was deemed a success. About the only drawbacks were the engine's 557-pound weight and its inherent secondary vertical shaking force.
In a phone interview, retired Pontiac engineer Malcolm R. "Mac" McKellar, who was deeply immersed in the development of the slant-four, recalled that vibration was pretty significant. "The bottom line is that at 195 cubic inches, it was too large a four-cylinder to be built without a balance shaft...We often referred to it as a 'traveling fatigue machine.'"
Indeed, almost all of the engine's accessory mounts had to be reinforced to deal with the constant shaking. Yet, amazingly, nearly all road tests of the day noted how smooth the car was to drive and how it was impossible to tell the engine was a four when driving it.
The secret was a combination of curved driveshaft, torque tube, and special motor mounts. The curved drive-shaft actually served two purposes. In addition to allowing for a nearly flat floor, it would not need the normal balancing procedures of a conventional rigid unit. The shaft's curvature and a pair of rubber bushings inside the torque-tube enclosure worked together to quell vibration. The last part of the equation was the use of special rubber "doughnut" motor mounts located at the front. They were constructed of soft rubber and were large enough to absorb much of the engine's vibration. The rear of the engine was located by the mounts of the transaxle and the torque tube.
"The four-cylinder Tempest was a smooth-driving car, but if a plug became fouled, as they sometimes would with leaded fuel, the mounts could not absorb the additional vibration," said McKellar. "You might not notice so much with a V-8, but with the slant-four, it would really vibrate."
Directly behind the engine was a bellhousing that was connected to the front of the torque tube. Manual-shift cars had the clutch located in the normal position. Both transaxles and the coil-spring, swing-axle rear suspension came from the Corvair and were modified to mate with the torque tube. A three-speed manual was standard; a Powerglide-based two-speed automatic -- "TempesTorque" -- was optional.
The front of the engine was tilted upward to meet the driveshaft and sat on a large box-section subframe, which also held the front suspension. The suspension itself was an independent design with coil springs, unequal-length upper and lower control arms, and ball joints, as well as a recirculating-ball steering box.
The drivetrain and suspension formed an integral, stand-alone unit. This feature allowed the Tempest to be built on the same assembly lines as the full-sized Pontiac, which used a "body-drop" assembly method to mate the Fisher body to the completed perimeter-frame chassis.
Of course, Pontiac engineers put just as much thought into the look of the Tempest as they did the design. On the next page, find out more about the look of the Pontiac Tempest.