Editing Iron Duke engine (section)

==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}}