The Iron Duke engine (also called 151, 2500, Pontiac 2.5, and Tech IV) is a Straight-4 piston engine built by the Pontiac Motor Division of General Motors from 1977 until 1993. Originally developed as Pontiac's new economy car engine, it was used in a wide variety of vehicles across GM's lineup in the 1980s as well as supplied to American Motors Corporation (AMC). The engine was engineered for fuel efficiency, smooth operation, and long life, not for performance. Total Duke engine production is estimated to be between 3.8 and 4.2 million units. Development At the time of the 1973 oil crisis the only engines Pontiac built were , , and versions of their V8 engine. Recognizing that future products would need to be smaller and more fuel-efficient, Pontiac engineers were tasked with developing a new engine that would be suitable for these future products. The engineers considered developing smaller displacement versions of the existing V8, a V6 derived from the V8, a V4 derived from the V8, and an inline-four derived from one of the cylinder banks of the V8 (in the same fashion the 1961 Pontiac Tempest's "Trophy 4" engine), but ultimately decided to create an entirely new four-cylinder engine. The development team's design goals were to minimize noise and vibration while maximizing durability, drivability, fuel economy, and "usable" power at lower engine speeds. They began by analyzing other four-cylinder engines in production at General Motors at the time, and they found that GM do Brasil's version of the Chevrolet 153 cu in four-cylinder—with a shorter stroke and longer connecting rods—had significantly reduced secondary vibration as compared to the original Chevrolet design and the newer 2.3 L four-cylinder from the Chevrolet Vega. This obviated the need for counter-rotating balance shafts, which would have increased the weight, complexity, and cost of the engine. Despite sharing the same bore, stroke, and cylinder spacing as the Brazilian engine, the majority of parts are not interchangeable. Focusing on making power at lower engine speeds was a deliberate consideration in order to meet the rest of the design goals. Careful consideration was made to the design of the intake manifold and exhaust gas recirculation system to ensure power output from each cylinder was equalized. Power consumption of the water and oil pumps were reduced, and the piston rings, cylinder bores, and crankshaft journals were designed to minimize friction. To maximize durability the engine block