Originally launched in 1977, this 2.5-liter inline-four engine, with its cast iron construction, was at the center of various GM models until 1993. According to Engine Builder magazine, It was one of GM’s first engines to use all-metric fasteners.
By all accounts, the Iron Duke had a simple design, but the specs were pretty impressive. With a bore and stroke of 4 inches and 3 inches, it initially had a compression ratio of 8.25:1, suitable for running on 87-octane fuel. Notably, the engine also underwent several improvements over its lifespan, including the introduction of throttle body injection in 1982, which gave it the Tech IV moniker. These advancements resulted in a peak output of 110 horsepower by the late 1980s.
Besides Pontiacs like the Astre, Phoenix, and Grand Am, GM also used the Iron Duke/Tech IV in some cool cars, like the Pontiac Firebird and the Fiero. Ironically, this gave the Iron Duke a bad reputation. The cars looked sporty, but the engine didn’t match up. So, in the end, conversations about the Duke got drowned by the more powerful engines.
There was, however, an interesting chapter in the Iron Duke’s story — its time in motorsports. Pontiac’s Super Duty division engineered a racing variant of the Iron Duke that participated in IMSA GT and low-level NASCAR, which could produce over 230 horsepower. It shows that with some changes, the Iron Duke could have done a lot more than what it was originally designed for.
