Iron Duke engine

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This article is about the automobile engine. For the steam locomotive, see
GWR Iron Duke Class
.
Iron Duke
GM 122 engine

The Iron Duke engine (also called 151, 2500, Pontiac 2.5, and Tech IV) is a 151 cu in (2.5 L)

piston engine built by the Pontiac Motor Division of General Motors from 1977 until 1993. Originally developed as Pontiac's new economy car engine, it was used in a wide variety of vehicles across GM's lineup in the 1980s as well as supplied to American Motors Corporation (AMC). The engine was engineered for fuel efficiency, smooth operation, and long life, not for performance.[2] Total Duke engine production is estimated to be between 3.8 and 4.2 million units.[3]

Development

At the time of the

cylinder banks of the V8 (in the same fashion as the 1961 Pontiac Tempest's "Trophy 4" engine), but ultimately decided to create an entirely new four-cylinder engine.[1]
: 1 

The development team's design goals were to minimize noise and vibration while maximizing durability,

cylinder spacing as the Brazilian engine, the majority of parts are not interchangeable.[1]
: 2 

Focusing on making power at lower engine speeds was a deliberate consideration in order to meet the rest of the design goals. Careful consideration was made to the design of the

intake manifold and exhaust gas recirculation system to ensure power output from each cylinder was equalized. Power consumption of the water and oil pumps were reduced, and the piston rings, cylinder bores, and crankshaft journals were designed to minimize friction.[1]
: 3–5 

To maximize durability the

overhead camshaft was eschewed in favor of an overhead valve design with timing gears. Specially-designed bolts that stretch slightly farther than a conventional bolt were used to secure the intake and exhaust manifolds to the cylinder head, to allow slight movement while maintaining the seal of the gaskets in order to prevent cracking the manifolds as they expand with heat.[1]
: 6–7 

A two-stage, two-barrel

air conditioning tended to experience drivability issues in hot weather, other improvements were made including a cut-off switch that shut the compressor off at wide open throttle and a delay incorporated into the air conditioning's circuitry to prevent the compressor from engaging until twelve seconds after the engine was started.[1]
: 7–10 

Early applications

The Iron Duke's first applications were in the 1977 Astre and Sunbird subcompact cars, replacing the 2.3 L Vega engine, and in the compact Phoenix. As these cars were originally designed for Chevrolet engines, the Iron Duke also used the Chevrolet bell housing bolt pattern, instead of the Buick-Oldsmobile-Pontiac V8 pattern. The following year use of the engine expanded to the Sunbird's Chevrolet and Oldsmobile twins, the Monza and Starfire.

For the 1979 model year, the engine was extensively redesigned. The original reverse-flow cylinder head was replaced by a crossflow design, a new two-barrel carburetor called "Vara-Jet" was introduced, the distributor was relocated, and the size of the oil pan was reduced. The only parts carried over from the 1978 engines were the connecting rods.[5] Peak power increased to 90 hp.

For 1980 the Iron Duke engine was redesigned to be mounted transversely, to suit the new

General Motors "X-body" cars. The bellhousing bolt pattern was revised to match that of the new 60° V6 engine
.

1982 AMC Spirit with Iron Duke

GM also began selling the engine to American Motors Corporation (AMC) starting with the 1980 model year. It was the base engine in Spirit, Concord, and Eagle automobiles, as well as in base-model Jeep CJs.[6] The engines purchased by AMC continued to use the Chevrolet V8 bellhousing pattern. The four-cylinder engine was discontinued from AMC's rear-wheel drive models after 1982. During 1983, the all-wheel drive Eagle base engine switched from the Iron Duke to a new, AMC-developed 150 cu in (2.5 L) four-cylinder. The 1980 through 1983 Jeep CJs were also available with the Iron Duke as the base engine.[7]

Year Power Torque
1978 85 hp (63 kW) @ 4400 rpm[8]: 40  123 lb⋅ft (167 N⋅m) @ 2800 rpm[8]: 40 
1979 90 hp (67 kW) 128 lb⋅ft (174 N⋅m)
1980 90 hp (67 kW) @ 4000 rpm[9]: 47  134 lb⋅ft (182 N⋅m) @ 2400 rpm[9]: 47 
1981 84 hp (63 kW) @ 4000 rpm[10] 125 lb⋅ft (169 N⋅m) @ 2400 rpm[10]
Applications:

Tech IV

"Tech IV" decal
"Tech IV" decal

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.[citation needed] Power output increased to 90 hp (67 kW).[11]

This was replaced by a swirl-port head with 9.0:1 (instead of 8.25:1) compression ratio in 1984 for a 2 hp (1.5 kW) gain. Other additions for 1985 included roller lifters, improved bearings, and a new

60-Degree V6. Over the years, the Tech IV engine has proved to be a reliable workhorse for owners when not pushed to its limits. All 1978-1990 Iron Duke engines used a micarta camshaft
gear that meshed directly with a steel gear on the crankshaft. 1991-92 VIN R and U engines used a timing chain instead.

The Grumman LLV (Long Life Vehicle) built from 1987 until 1994 for the United States Postal Service for use in mail delivery were initially powered by the Iron Duke engine. The Postal Service specifications called for a 24-year service life and those with 2.5 L engine have surpassed expectations.[12]

  • "Tech IV" engine
    "Tech IV" engine
  • 1990 GM Iron Duke engine with parts cut away to reveal the inner arrangement
    1990 GM Iron Duke engine with parts cut away to reveal the inner arrangement
Applications:

Super Duty

Super Duty Engine Displacements
Displacement Stroke
2.1 L (131 cu in) 2+3⁄5 in (66.0 mm)
2.5 L (151 cu in) 3 in (76.2 mm)
2.7 L (163 cu in) 3+1⁄4 in (82.6 mm)
3.0 L (182 cu in) 3+5⁄8 in (92.1 mm)
3.2 L (198 cu in) 3+15⁄16 in (100.0 mm)

The Iron Duke block formed the basis of Pontiac's Super Duty four-cylinder racing engines of the 1980s, the last in a line of high-performance Pontiac Super Duty engines. The engines were featured in NASCAR's Charlotte/Daytona Dash Series, the IMSA GT Championship (in GTP and GTU class cars), and even in American Power Boat Association racing boats. Super Duty engines continued to be used in ARCA racing until well into the 2000s.

In addition to parts matching the Iron Duke's stock 2.5 L displacement other crankshafts and their corresponding connecting rods were offered by Pontiac Motorsports, resulting in displacements ranging from 2.1 L to 3.2 L. A 2.7 L, 232 hp (173 kW) Super Duty engine powered the 1984 Fiero Indy Pace Car to over 138 mph (222 km/h) during the race, but Super Duty engines were never available in factory-built GM vehicles. However, GM sold the Super-Duty-specific parts at authorized dealers and all of the parts required to convert a stock Iron Duke engine to a Super Duty version were available.

Kansas Racing Products continued to make the engines in the early 21st century after buying rights to make them from GM.

Cosworth also produced a 16-valve, double-overhead cam head for the 3.0 L version of the racing engine (Cosworth Project DBA, 1987).[13]

References

  • 1979 Chevy Monza Brochure
  1. ^ a b c d e f g h i Sawruk, John M. (26–30 September 1977). Pontiac's New 2.5 Litre 4 Cylinder Engine (PDF). Society of Automotive Engineers: Passenger Car Meeting. Detroit. Archived from the original (PDF) on 5 February 2018. Retrieved 17 August 2019.
  2. ^ Hunting, Benjamin (May 26, 2021). "GM's Unkillable Iron Duke 4-Cylinder Engine Powered Dozens Of Trucks, Cars, and SUVs For Decades". DrivingLine. Retrieved January 20, 2023.
  3. ^ Appel, Tom (September 12, 2018). "What Was The Iron Duke?". The Daily Drive by Consumer Guide. Retrieved January 20, 2023.
  4. ^ Strohl, Daniel (September 20, 2019). "For the last time, the Iron Duke was not the same engine as the Chevy II four-cylinder". Hemmings. Retrieved January 20, 2023.
  5. ^ Weissler, Paul (November 1978). "Servicing the '79 GM Cars". Popular Mechanics. pp. 162–164. Retrieved 17 August 2019.
  6. ^ Martin, Murilee (11 October 2017). "1982: Luxurious AMC Concord gets Ziebart no-rust, GM Iron Duke power". Autoweek. Retrieved January 20, 2023.
  7. ^ "Jeep Engine: GM 151". jeeptech.com. December 1, 2010. Retrieved January 20, 2023.
  8. ^
    Dunne, Jim; Jacobs, Ed (August 1978). "Small-engine sport sedans—good handling, tame performance"
    . Popular Science. Retrieved 18 August 2019.
  9. ^ a b Dunne, Jim; Jacobs, Ed (July 1979). "GM's X-cars challenge traditional compacts". Popular Science. Retrieved 18 August 2019.
  10. ^ a b Dunne, Jim; Jacobs, Ed (March 1981). "U.S. compacts: Is Chrysler's K-car the new champ?". Popular Science. p. 46. Retrieved 27 August 2019.
  11. ^ Dunne, Jim (February 1982). "Are carburetors kaput? Coming: throttle-body injection". Popular Science. p. 52. Retrieved 27 August 2019.
  12. ^ Weinstein, Joshua (June 8, 2022). "GM 2.5L Iron Duke I4 Engine Guide". Junkyard Mob. Retrieved January 20, 2023.
  13. ^ "Cosworth Type Reference". Race-cars.com. Archived from the original on 2011-02-22. Retrieved 2012-06-04.

External links

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