GM Iron Duke engine
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The Iron Duke (also called the 2500, 151, Pontiac 2.5, Cross Flow, and Tech IV, though on a 1987 Pontiac 6000's air filter assembly it actually reads "4 Tech") was a 2.5 L (151 in³) I4 piston engine. All Iron Dukes were built by Pontiac beginning in 1977 and ending in 1993. Jeep also used it (as the Hurricane) in the Jeep CJ. It used an iron block and head, pushrods, and had a 4 in (101.6 mm) bore and 3 in (76.2 mm) stroke.
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. One thing that both share is the Chevrolet Small-Block bellhousing bolt pattern.
Applications:
- 1977 Pontiac Astre
- 1978-1980 Pontiac Sunbird
- 1984-1988 Pontiac Fiero
- 1982-1985 Chevrolet Camaro
- 1985-1990 Chevrolet Astro
- 1985-1990 GMC Safari
- Chevrolet S-10
- Chevrolet S-10 Blazer
- GMC Sonoma
- GMC S-15 Jimmy
- Chevrolet Monza
- Buick Skylark
- Buick Skyhawk
- Pontiac 6000
- Oldsmobile Omega
| Year | hp (kW) | ft·lbf (N·m) |
|---|---|---|
| 1978 | 85 (63) | 123 (167) |
| 1979 | 90 (67) | 128 (173) |
| 1980 | 86 (64) | 128 (173) |
Contents |
LS6
The LS6 was a 151 in³ (2.5 L) I4 engine produced from 1978 to 1979.
LS8
The LS8 was a 151 in³ (2.5 L) I4 engine produced from 1979 to 1979.
LX6
The LX6 was a 151 in³ (2.5 L) I4 engine produced from 1977 to 1978.
LX8
The LX8 was a 151 in³ (2.5 L) I4 engine produced from 1979 to 1980.
Crossflow
Cross-flow cylinder heads were added in 1980, leading people to refer to this version as the crossflow. Output stood at 90 hp (67 kW).
AMC/Jeep
Several American Motors models used the Iron Duke from 1980 to 1983, before AMC had finished its own 2.5 L I4. Output was 82 hp (61 kW).
Applications:
Tech IV
Iron Dukes were fitted with fuel injection (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. The engine was updated one final time the next year with balance shafts, new pistons, rods, crankshaft, and an in-pan oiling system. This 1988 Tech IV produced 98 hp (73 kW).
The Tech IV uses the same bellhousing pattern as the 2.8 L 60-Degree V6.
Applications:
- 1985-1993 Chevrolet S-10 Blazer/GMC S-15 Jimmy
- 1984-1988 Pontiac Fiero
- 1985-1991 Pontiac Grand Am, Pontiac 6000, Oldsmobile Cutlass Calais
- 1985-1987 Buick Somerset
- 1986-1991 Buick Skylark
Racing versions
Though not a production engine, the Super Duty 4 racing engine was notable and widely publicized at the time. It was the basis for NASCAR's Touring Car series.
Cosworth also produced a 16-valve head for the Iron Duke.