Iron Duke engine

Motor vehicle engine

The Iron Duke engine (also called 151, 2500, Pontiac 2.5, and Tech IV) is a 151:cu:in (2.5:L) Straight-4 piston engine built by the Pontiac Motor Division of General Motors from 1977 to 1993. Thereafter GM's 2.2:L OHV 4-cylinder replaced it across the entire lineup of vehicles that offered it. Although its original purpose was to serve as Pontiac's new economy car engine, it was later adapted for use in a wide variety of applications across GM's lineup in the 1980s.



At the time of the 1973 oil crisis the only engines Pontiac built were 350:cu:in (5.7:L), 400:cu:in (6.6:L), and 455:cu:in (7.5:L) 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.:1

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.:1 They began by analyzing other four-cylinder engines in production at General Motors at the time, and they found that GM do Brasil's 151:cu:in (2.5:L) version of the Chevrolet 153 cu in four-cylinder—with a shorter 3-inch (76:mm) stroke and longer 6-inch (150:mm) 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.:1-2 This obviated the need for counter-rotating balance shafts, which would have increased the weight, complexity and cost of the engine.:3 Despite sharing the same more

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