GM Iron Duke engine
|Bore||4 in (101.6 mm)|
|Stroke||3 in (76.2 mm)|
|Displacement||151 cu in (2.5 L)|
|Power output||85 hp (63 kW)|
|Specific power||0.56 hp/cu in (25.2 kW/L)|
|Torque output||123 ft·lbf (167 N·m)|
The Iron Duke (also called the 2500, 151, Pontiac 2.5, Cross Flow, and Tech IV, though the decal on the air filter assemblies actually reads "4 Tech") was a 2.5 L (151 cu in) I4 piston engine. All Iron Dukes were built by Pontiac beginning in 1977 and ending in 1993.
This 151 was also used by American Motors (AMC) starting in 1980, as the base engine option in the RWD Spirit and Concord, and continuing in both cars through 1982. The AWD (4x4) Eagle carried the 151 as standard equipment for 1981, and carried it midway through the 1983 model year. It was also available (as the Hurricane) in economy model Jeep CJs. AMC replaced the Iron Duke 2.5L I4 with a 150cid Inline-4 of their own, derived from their evergreen sixes.
The Iron Duke is often confused with Chevrolet's Stovebolt-derived 153 from the 1960s Chevy II, but the engines are entirely different - the Iron Duke's intake manifold is on the passenger side, as opposed to the driver side.
- 1977 Pontiac Astre
- 1977-1980 Pontiac Sunbird
- 1984-1988 Pontiac Fiero
- 1982-1985 Pontiac Firebird
- 1982-1985 Chevrolet Camaro
- 1985-1990 Chevrolet Astro
- 1985-1990 GMC Safari
- Chevrolet Citation
- Chevrolet Celebrity
- Chevrolet S-10
- Chevrolet S-10 Blazer
- GMC Sonoma
- GMC S-15 Jimmy
- Chevrolet Monza
- Buick Skylark
- Buick Skyhawk
- Buick Century
- Pontiac 6000
- 1985-1991 Pontiac Grand Am
- Oldsmobile Ciera
- Oldsmobile Omega
- AMC Concord/Spirit (1980-82)
- Eagle (1981-83)
- Jeep CJ (1980-83)
- Grumman LLV United States Postal Service delivery vehicle
|Year||hp (kW)||ft·lbf (N·m)|
|1978||85 (63)||123 (167)|
|1979||90 (67)||128 (173)|
|1980||86 (64)||128 (173)|
The LS6 was a 151 cu in (2.5 L) I4 engine produced from 1978 to 1979.
The LS8 was a 151 cu in (2.5 L) I4 engine produced for 1979.
The LX6 was a 151 cu in (2.5 L) I4 engine produced from 1977 to 1978.
The LX8 was a 151 cu in (2.5 L) I4 engine produced from 1979 to 1980.
Cross-flow cylinder heads were added in mid-1979, leading people to refer to this version as the crossflow. Output stood at 90 hp (67 kW).
|Also called||Iron Duke|
Iron Dukes were fitted with fuel injection (TBI, via a single injector in the throttle body) in 1982. This version was christened the Tech IV, though Car and Driver later ridiculed it as the low-Tech IV. Power output remained at 90 hp (67 kW).
This was replaced by a swirl-port head with 9.0:1 (instead of 8.2:1) compression ratio in 1984 for a 2 hp (1.5 kW) gain. Other additions for 1985 included roller lifters, improved bearings, and a new crankshaft.
A more-modern serpentine belt and crank-triggered ignition was added in 1987, increasing horsepower to 98. The engine was updated one final time one year later with balance shafts, new pistons, rods, crankshaft, and an in-pan oiling system. This 1988 Tech IV produced 110 hp (73 kW).
The Tech IV uses the same bellhousing pattern as the 2.8 L 60-Degree V6.
Over the years, the Tech IV engine has proved to be a reliable, if noisy, workhorse for owners--when not pushed to its limits. All 1978-1990 Iron Duke L-4's are outfitted with a micarta camshaft gear that meshes directly with a steel gear on the crankshaft (no timing chain). 1991-92 VIN R and U engines received a timing chain. The timing gear has a tendency to crumble a tooth anytime after 80,000 miles . The cam gear simply shears a tooth at startup and the engine won't start. When the cam gear loses a tooth, the camshaft AND distributor stop rotating during engine cranking.
Replacing the gear requires heating the new gear in hot oil and quickly installing it for a press fit on the cam stub
A few Tech IV owners experience minor driveability issues with the engine. There are several cheap/easy repairs that the shadetree mechanic can perform to keep this engine running at its best.
Inspection (and replacement, if necessary) of the MAP sensor, and its accompanying vacuum hose, is often a solution to many driveability problems. This sensor largely controls the engine's driveability. Stuck EGR valves are also very common on the Tech IV. When replacing the EGR, a mechanic should only use a new, Delphi-sourced or AC Delco part, as aftermarket EGR valves have diaphram springs that are too weak for this engine. This causes hesitation, sag, stumbling, and sometimes, hard starting. Oxygen sensors should also be replaced every 30,000 miles (48,000 km) on this engine.
- 1985-1993 Chevrolet S-10/GMC S-15 Sonoma
- 1985-1994 Chevrolet Astro
- 1990-1992 Chevrolet Lumina
- 1984-1988 Pontiac Fiero
- 1982-1985 Chevrolet Citation II
- 1982-1984 Pontiac Phoenix, Oldsmobile Omega
- 1982-1991 Pontiac 6000, Chevrolet Celebrity, Oldsmobile Cutlass Ciera, Buick Century
- 1985-1991 Pontiac Grand Am, Oldsmobile Cutlass Calais, Buick Somerset, Buick Skylark
- 1982-1986 Pontiac Firebird and Chevrolet Camaro