 Unless customers checked an option, the Tempest's power plant was a 194.5 CID inline slant-four cylinder motor, derived from the right bank of the venerable Pontiac 389 V8, enabling it to be run down the same production line as the 389, saving costs for both the car's customers and Pontiac.Pontiac engineers ran early tests of this motor by literally cutting off the left bank of pistons and adding counterweights to the crankshaft, and were surprised to find it easily maintained the heaviest Pontiacs at over .In production, the engine received a crankshaft designed for just four cylinders, but this did not completely solve its balance issues.