80s Engines: The Iron Duke

This month, we’re starting a new post category on Eighties Cars—engines. They won’t always be the most powerful or most interesting engines, just ones that were relevant in the 1980s.

Cross section of the original Iron Duke

GM’s Iron Duke 2.5 liter/151 ci inline four was one of the least glamorous but most important engines of the eighties. Despite its strong association with the 1980s, the Iron Duke was developed by Pontiac in the mid-1970s and was in use until the early 1990s.

The Iron Duke name was inspired by the new engine’s cast-iron block, with that material chosen for durability. Pontiac used the Iron Duke branding in advertising, perhaps to ensure that potential buyers didn’t associate their new four with the Chevrolet Vega’s extremely unsuccessful aluminum four. Other notable characteristics of the Iron Duke included overhead valves and a relatively short stroke.

The Iron Duke was reasonably reliable, got acceptable fuel economy, and had impressive torque for an inline four. However, Pontiac’s engine wasn’t refined, powerful, or quiet—especially compared to some of the fours that started coming from Europe and Japan during the eighties. The Iron Duke had no balance shafts until 1989, and it never received port fuel injection.

Model yearChanges/NotesBHPTorque
1980Modified for transverse applications90134
1981Emissions changes84125
1982Throttle-body fuel injection (Tech IV)90132
198390132
1984Compression ratio increased to 9.0:192132
198592132
198692132
198792132
1988Heads redesigned98135
1989Balance shafts98135
The Iron Duke in the 1980s—not all vehicles got updates in the same model year

General Motors used the Iron Duke in every one of its North American marques but Cadillac, and it appeared in dozens of sedans, coupes, wagons, trucks, and SUVs. The Iron Duke was also available in a few wildly inappropriate vehicles—notable examples are the Chevrolet Camaro Sport Coupe, the Pontiac Firebird base coupe and S/E, and the Pontiac Fiero. GM also sold the Iron Duke to AMC, where it appeared in the Concord, the Eagle, the Spirit, and the Jeep CJ.

An Iron Duke-equipped vehicle may have driven by you today—most of the Grumman LLVs that the US Postal Service uses are equipped with one.