Editing Iron Duke engine

{{about|the automobile engine|the steam locomotive|GWR Iron Duke Class}}
{{Infobox automobile engine
| image = Iron Duke^ 2.5L four cylinder engine - Flickr - dave 7.jpg
| name = Iron Duke
| aka = Tech IV (1982-1990)
| manufacturer = [[General Motors]]
| production = 1977–1993
| predecessor = [[GM 2300 engine]]
| successor = [[GM 122 engine]]
| bore = {{cvt|4|in|mm|1}}
| stroke = {{cvt|3|in|mm|1}}
| configuration = [[Straight-four]]
| displacement = {{cvt|2471|cc|CID L cc|1|adj=ri0|order=out}}
| length = 
| width = 
| height = 
| weight = {{cvt|375|lb|kg}}<ref name="SAE770819">{{cite conference |last=Sawruk |first=John M. |title=Pontiac's New 2.5 Litre 4 Cylinder Engine |conference=Society of Automotive Engineers: Passenger Car Meeting |date=26–30 September 1977 |location=Detroit |url= https://gafiero.akroncdnr.com/docs/IronDuke.pdf |access-date=17 August 2019 |archive-url= https://web.archive.org/web/20180205132841/https://gafiero.akroncdnr.com/docs/IronDuke.pdf |archive-date=5 February 2018}}</ref>{{rp|3}}
| block = [[Cast iron]]
| head = [[Cast iron]]
| valvetrain = [[Overhead valve engine|OHV]] 2 valves x cyl.
| fuelsystem = [[Carburetor]]<br/>[[Throttle-body fuel injection]]
| fueltype = [[Gasoline]]
| oilsystem = [[Wet sump]]
| coolingsystem = [[Radiator (engine cooling)|Water-cooled]]
| power = {{cvt|85–110|hp|kW|0}}
| specpower = {{cvt|{{#expr:85/2.471 round 1}}|hp|kW|1}}-{{cvt|{{#expr:110/2.471 round 1}}|hp|kW|1}} per liter
| torque = {{cvt|123–135|lbft|Nm|0}}
| compression = 8.25:1 (1977–1983) 9.0:1 (1984–1993)
| redline = 5000&nbsp;rpm
}}

The '''Iron Duke engine''' (also called '''151''', '''2500''', '''Pontiac 2.5''', and '''Tech IV''') is a {{cvt|151|cuin|L|1}} [[straight-4]] [[piston engine]] built by the [[Pontiac (automobile)|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.<ref>{{cite web |last1=Hunting |first1=Benjamin |title=GM's Unkillable Iron Duke 4-Cylinder Engine Powered Dozens Of Trucks, Cars, and SUVs For Decades |date=May 26, 2021 |url= https://www.drivingline.com/articles/gms-unkillable-iron-duke-engine-powered-dozens-of-trucks-cars-and-suvs-for-decades/ |work=DrivingLine |access-date=January 20, 2023}}</ref> Total Duke engine production is estimated to be between 3.8 and 4.2 million units.<ref>{{cite web |last1=Appel |first1=Tom |title=What Was The Iron Duke? |url= https://blog.consumerguide.com/what-was-the-iron-duke/ |work=The Daily Drive by Consumer Guide |access-date=January 20, 2023 |date=September 12, 2018}}</ref>

{{TOC limit|3}}

==Development==

At the time of the [[1973 oil crisis]] the only engines Pontiac built were {{cvt|350|cuin|L|1}}, {{cvt|400|cuin|L|1}}, and {{cvt|455|cuin|L|1}} versions of [[Pontiac V8 engine|their V8 engine]]. Recognizing that future products would need to be smaller and more fuel-efficient, Pontiac engineers were tasked with developing a new engine that would be suitable for these future products.<ref>{{cite web |last1=Strohl |first1=Daniel |title=For the last time, the Iron Duke was not the same engine as the Chevy II four-cylinder |url= https://www.hemmings.com/stories/2019/09/20/for-the-last-time-the-iron-duke-was-not-the-same-engine-as-the-chevy-ii-four-cylinder |work=Hemmings |date=September 20, 2019 |access-date=January 20, 2023}}</ref> The engineers considered developing smaller displacement versions of the existing V8, a [[V6 engine|V6]] derived from the V8, a [[V4 engine|V4]] derived from the V8, and an inline-four derived from one of the [[cylinder bank]]s of the V8 (in the same fashion as the [[Pontiac Tempest#First generation (1961–1963)|1961 Pontiac Tempest]]'s [[Pontiac Trophy 4 engine|"Trophy 4" engine]]), but ultimately decided to create an entirely new four-cylinder engine.{{r|SAE770819|p=1}}

The development team's design goals were to minimize noise and vibration while maximizing durability, [[wiktionary:drivability|drivability]], fuel economy, and "usable" power at lower engine speeds.{{r|SAE770819|p=1}} They began by analyzing other four-cylinder engines in production at General Motors at the time, and they found that [[General Motors do Brasil|GM do Brasil]]'s {{cvt|151|cuin|L|1}} version of the [[Chevrolet 153 4-cylinder engine|Chevrolet 153 cu in four-cylinder]]—with a shorter {{convert|3|in|adj=on}} [[Stroke (engine)#Stroke length|stroke]] and longer {{convert|6|in|adj=on}} [[connecting rod]]s—had significantly reduced [[Engine balance#Secondary vibration|secondary vibration]] as compared to the original Chevrolet design and the newer [[Chevrolet 2300 engine|2.3-liter four-cylinder]] from the [[Chevrolet Vega]].{{r|SAE770819|pp=1-2}} This obviated the need for [[balance shaft|counter-rotating balance shafts]], which would have increased the weight, complexity, and cost of the engine.{{r|SAE770819|p=3}} Despite sharing the same [[Bore (engine)|bore]], stroke, and [[Bore pitch|cylinder spacing]] as the Brazilian engine, the majority of parts are not interchangeable.{{r|SAE770819|p=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 ring]]s, cylinder bores, and crankshaft journals were designed to minimize friction.{{r|SAE770819|pp=3-5}}

To maximize durability the [[engine block]] was made of cast iron with five [[main bearing]]s, rather than the relatively fragile cast aluminum block used by the 2.3-liter Vega engine. (Even with the cast iron block the Iron Duke only weighed about 20 pounds more.) The 2.3-liter engine's [[timing belt (camshaft)|belt-driven]] [[overhead camshaft]] was eschewed in favor of an [[overhead valve engine|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 [[thermal expansion|expand with heat]].{{r|SAE770819|pp=6-7}}

A two-stage, two-barrel [[carburetor]] with electric [[choke valve|choke]] was used to improve performance in cold starts, while heat shields incorporated underneath the carburetor and between the intake and exhaust manifolds were used to prevent heat soaking the gasoline in the carburetor thereby improving performance in hot weather. Recognizing that cars with four-cylinder engines equipped with [[automobile air conditioning|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.{{r|SAE770819|pp=7-10}}

==Early applications==

The Iron Duke's first applications were in the 1977 [[Pontiac Astre|Astre]] and [[Pontiac Sunbird#First generation (1976–1980)|Sunbird]] subcompact cars, replacing the 2.3-liter Vega engine, and in the compact [[Pontiac Phoenix#First generation (1977–1979)|Phoenix]]. As these cars were originally designed for Chevrolet engines, the Iron Duke also used the Chevrolet [[bell housing|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 [[Chevrolet Monza|Monza]] and [[Oldsmobile Starfire#Second generation (1975–1980)|Starfire]].

For the 1979 model year, the engine was extensively redesigned. The original [[reverse-flow cylinder head]] was replaced by a [[Crossflow cylinder head|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.<ref name="PopMech1978">{{cite magazine|last=Weissler |first=Paul |date=November 1978 |title=Servicing the '79 GM Cars |url= https://books.google.com/books?id=oM8DAAAAMBAJ |pages=162–164 |magazine=Popular Mechanics |access-date=17 August 2019}}</ref> Peak power increased to 90&nbsp;hp.

For 1980 the Iron Duke engine was redesigned to be mounted transversely, to suit the new [[front-wheel-drive|front-drive]] [[GM X platform (1980)|General Motors "X-body" cars]]. The bellhousing bolt pattern was revised to match that of the new [[General Motors 60° V6 engine|60° V6 engine]].

[[File:1982 AMC Spirit liftback in Vintage Red metallic at PA meet 7of8.jpg|thumb|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 [[AMC Spirit|Spirit]], [[AMC Concord|Concord]], and [[AMC Eagle|Eagle]] automobiles, as well as in base-model [[Jeep CJ]]s.<ref>{{cite web |last1=Martin |first1=Murilee |title=1982: Luxurious AMC Concord gets Ziebart no-rust, GM Iron Duke power |url= https://www.autoweek.com/car-life/classic-cars/a1832536/1982-luxurious-amc-concord-gets-ziebart-no-rust-gm-iron-duke-power/ |work=Autoweek |date=11 October 2017 |access-date=January 20, 2023}}</ref> 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 {{cvt|150|cid|L|1}} [[AMC straight-4 engine|four-cylinder]]. The 1980 through 1983 Jeep CJs were also available with the Iron Duke as the base engine.<ref>{{cite web |title=Jeep Engine: GM 151 |url= https://www.jeeptech.com/engine/gm151.html |website=jeeptech.com |date=December 1, 2010 |access-date=January 20, 2023}}</ref>

{| cellpadding="2" cellspacing="2" style="margin:0 0 1em 1em; border:3px solid skyBlue;"
|-
!Year
!Power
!Torque
|-
|1978
|{{cvt|85|hp|kW|0}} at 4400&nbsp;rpm<ref name="PopSci1978">{{cite magazine|title=Small-engine sport sedans—good handling, tame performance |date=August 1978 |author-link=Jim Dunne (automotive spy photographer) |first1=Jim |last1=Dunne |last2=Jacobs |first2=Ed |magazine=Popular Science |url= https://books.google.com/books?id=BwEAAAAAMBAJ |access-date=18 August 2019}}</ref>{{rp|40}}
|{{cvt|123|lbft|Nm|0}} at 2800&nbsp;rpm{{r|PopSci1978|p=40}}
|-
|1979
|{{cvt|90|hp|kW|0}}
|{{cvt|128|lbft|Nm|0}}
|-
|1980
|{{cvt|90|hp|kW|0}} at 4000&nbsp;rpm<ref name="PopSciXcars">{{cite magazine|title=GM's X-cars challenge traditional compacts |date=July 1979 |first1=Jim |last1=Dunne |last2=Jacobs |first2=Ed |magazine=Popular Science |url= https://books.google.com/books?id=NQEAAAAAMBAJ |access-date=18 August 2019}}</ref>{{rp|47}}
|{{cvt|134|lbft|Nm|0}} at 2400&nbsp;rpm{{r|PopSciXcars|p=47}}
|-
|1981
|{{cvt|84|hp|kW|0}} at 4000&nbsp;rpm<ref name="PopSci1981">{{cite magazine|first1=Jim |last1=Dunne |last2=Jacobs |first2=Ed |date=March 1981 |title=U.S. compacts: Is Chrysler's K-car the new champ? |url= https://books.google.com/books?id=z7nkfLrLoMsC |page=46 |magazine=Popular Science |access-date=27 August 2019}}</ref>
|{{cvt|125|lbft|Nm|0}} at 2400&nbsp;rpm{{r|PopSci1981}}
|}

{{hidden begin
|title      = Applications:
|titlestyle = background:#88FF88; text-align:left;
|bodystyle  = text-align:left;
}}
* 1981–1982 [[AMC Concord]]
* 1981–1983 [[AMC Eagle]]
* 1980–1982 [[AMC Spirit]]
* 1980–1981 [[Buick Skylark]]
* 1980–1981 [[Chevrolet Citation]]
* 1978–1980 [[Chevrolet Monza]]
* 1980–1983 [[Jeep CJ]]
* 1980–1981 [[Oldsmobile Omega]]
* 1978–1980 [[Oldsmobile Starfire]]
* 1977 [[Pontiac Astre]]
* 1977–1981 [[Pontiac Phoenix]]
* 1977–1980 [[Pontiac Sunbird]]
* 1977 [[Pontiac_Ventura#1971–1977|Pontiac Ventura]]
{{hidden end}}

==Tech IV==
[[File:GM Engine Tech4.png|right|"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|date=August 2019}} Power output increased to {{cvt|90|hp|kW|0}}.<ref name="PopSciTBI">{{cite magazine|title=Are carburetors kaput? Coming: throttle-body injection |date=February 1982 |last=Dunne |first=Jim |magazine=Popular Science |page=52 |url= https://books.google.com/books?id=GbTTw-z6NH0C |access-date=27 August 2019}}</ref>

This was replaced by a swirl-port head with 9.0:1 (instead of 8.25:1) compression ratio in 1984 for a {{cvt|2|hp|kW}} gain. Other additions for 1985 included roller lifters, improved bearings, and a new [[crankshaft]]. Several significant changes were made in 1987, which included: an improved cylinder head, intake manifold, and [[throttle-body fuel injection]] module; a more-modern serpentine belt with an automatic spring-loaded tensioner for the accessories; and a [[Distributorless Ignition System]] (DIS). This revision to the engine increased power to {{cvt|98|hp|kW|0}}. In 1988, a [[balance shaft]] was added to smooth engine vibrations. Up to this point, the engine incorporated a 'dogbone' upper front engine mount secured to the cowling of the vehicle's hood latch, aiding in controlling the vibration. Further improvements in later years included new pistons, rods, crankshaft, and an in-pan oiling system. The most powerful variant of the Tech IV raised the rev limit to 5500&nbsp;rpm, and achieved {{cvt|110|hp|kW|0}}. The Tech IV uses the same [[Bell housing|bellhousing]] pattern as the 2.8-liter ''[[GM 60-Degree V6 engine|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-liter engine have surpassed expectations.<ref>{{cite web |last1=Weinstein |first1=Joshua |title=GM 2.5L Iron Duke I4 Engine Guide |url=https://www.junkyardmob.com/guides/gm-iron-duke |work=Junkyard Mob |date=June 8, 2022 |access-date=January 20, 2023}}</ref>

<gallery widths="200px" heights="200px">
File:2.5l tech 4 engine.jpg|"Tech IV" engine
File:1990 GM Iron Duke engine cut-away exhibit.jpg|1990 GM Iron Duke engine with parts cut away to reveal the inner arrangement
</gallery>

{{hidden begin
|title      = Applications:
|titlestyle = background:#88FF88; text-align:left;
|bodystyle  = text-align:left;
}}
* 1982–1992 [[Buick Century]]
* 1982–1991 [[Buick Skylark]]
* 1985–1987 [[Buick Somerset|Buick Somerset/Somerset Regal]]
* 1985–1990 [[Chevrolet Astro]] Cargo Van
* 1982–1985 [[Chevrolet Camaro]] 
* 1982–1990 [[Chevrolet Celebrity]]
* 1990–1992 [[Chevrolet Lumina]]
* 1985–1993 [[Chevrolet S-10]]
* 1985–1987 [[Chevrolet S-10 Blazer]]
* 1985–1987 [[Chevrolet S-10 Blazer|GMC S-15 Jimmy]]
* 1985–1993 [[Chevrolet S-10|GMC S-15/GMC Sonoma]]
* 1985–1990 [[Chevrolet Astro|GMC Safari]] Cargo Van
* 1987–1994 [[Grumman LLV]] ([[United States Postal Service|USPS]] delivery vehicle)
* 1985–1991 [[Oldsmobile Calais|Oldsmobile Calais/Cutlass Calais]]
* 1982–1992 [[Oldsmobile Cutlass Ciera]]
* 1982–1991 [[Pontiac 6000]]
* 1984–1988 [[Pontiac Fiero]]
* 1982–1985 [[Pontiac Firebird]]
* 1985–1991 [[Pontiac Grand Am]]
{{hidden end}}

==Super Duty==
{| class="wikitable floatright"
|+''Super Duty'' Engine Displacements
|-
! Displacement
! Stroke
|-
|{{cvt|131|CID|L|1|disp=flip}}
|{{cvt|2+3/5|in|mm|1}}
|-
|{{cvt|151|CID|L|1|disp=flip}}
|{{cvt|3|in|mm|1}}
|-
|{{cvt|163|CID|L|1|disp=flip}}
|{{cvt|3+1/4|in|mm|1}}
|-
|{{cvt|182|CID|L|1|disp=flip}}
|{{cvt|3+5/8|in|mm|1}}
|-
|{{cvt|198|CID|L|1|disp=flip}}
|{{cvt|3+15/16|in|mm|1}}
|}

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 [[Pontiac V8 engine#Super Duty|high-performance Pontiac Super Duty engines]]. The engines were featured in [[NASCAR]]'s [[ISCARS Dash Touring Series|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 [[Automobile Racing Club of America|ARCA]] racing until well into the 2000s.

In addition to parts matching the Iron Duke's stock 2.5-liter displacement other crankshafts and their corresponding connecting rods were offered by Pontiac Motorsports, resulting in displacements ranging from 2.1-liters to 3.2-liters. A 2.7-liter, {{cvt|232|hp|kW|0}} Super Duty engine powered the 1984 [[Pontiac Fiero|Fiero]] [[Indianapolis 500 pace cars|Indy Pace Car]] to over {{cvt|138|mph|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 [[Multi-valve#Four valves|16-valve]], double-overhead cam head for the 3.0-liter version of the racing engine ([[Cosworth]] Project DBA, 1987).<ref name="Cosworth Type Reference">{{cite web |url=http://www.race-cars.com/utility/coswrthr.htm |title=Cosworth Type Reference |website=Race-cars.com |access-date=2012-06-04 |archive-date=2011-02-22 |archive-url=https://web.archive.org/web/20110222090951/http://www.race-cars.com/utility/coswrthr.htm |url-status=dead }}</ref>

==References==
* 1979 Chevy Monza Brochure
{{reflist}}

==External links==
{{Commons cat}}
* [http://www.jeeptech.com/engine/gm151.html Jeep 151 information]

{{GM late engine timeline}}

[[Category:Gasoline engines by model]]
[[Category:Pontiac engines|Iron Duke]]
[[Category:Straight-four engines]]