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Iron Duke engine
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Iron Duke engine
The Iron Duke engine (also called 151, 2500, Pontiac 2.5, and Tech IV) is a 151 cu in (2.5 L) straight-4 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. Total Duke engine production is estimated to be between 3.8 and 4.2 million units.
At the time of the 1973 oil crisis the only engines Pontiac built were 350 cu in (5.7 L), 400 cu in (6.6 L), and 455 cu in (7.5 L) versions of 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. The engineers considered developing smaller displacement versions of the existing V8, a V6 derived from the V8, a V4 derived from the V8, and an inline-four derived from one 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. The 'all-new' claim was partially marketing terminology as many of the external parts, such as the distributor, water pump, manifolds, and carburetor were taken directly from the earlier Chevrolet 4-cylinder engine some with small dimensional changes making them non–interchangeable. Further confusion is due to the bare blocks looking visually nearly identical even though almost none of the internal parts are interchangeable between the two engine series. Borrowing parts like this greatly reduced development, tooling, and production time and costs. The early few years of the Iron Duke are more closely related to the earlier Chevrolet 4-cylinder than the later versions with numerous design changes such as fuel injection, flat belt accessory drive, cross flow heads, and balance shafts. Interestingly, the water pump from the late production years will bolt onto a first year production 1961 Chevrolet 151 4-cylinder engine, although designed for reverse rotation.
The development team's design goals were to minimize noise and vibration while maximizing durability, drivability, fuel economy, and "usable" power at lower engine speeds. They began by analyzing other four-cylinder engines in production at General Motors at the time, and they found that GM do Brasil's 151 cu in (2.5 L) version of the Chevrolet 153 cu in four-cylinder—with a shorter 3-inch (76 mm) stroke and longer 6-inch (150 mm) connecting rods—had significantly reduced secondary vibration as compared to the original Chevrolet design and the newer 2.3-liter four-cylinder from the Chevrolet Vega. This obviated the need for counter-rotating balance shafts, which would have increased the weight, complexity, and cost of the engine. Despite sharing the same bore, stroke, and cylinder spacing as the Brazilian engine, the majority of parts are not interchangeable.
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.
To maximize durability the engine block was made of cast iron with five main bearings, 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 belt-driven 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.
A two-stage, two-barrel carburetor with electric 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 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.
The Iron Duke's first applications were in the 1977 Astre and Sunbird subcompact cars, replacing the 2.3-liter 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. Peak power increased to 90 hp.
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Iron Duke engine
The Iron Duke engine (also called 151, 2500, Pontiac 2.5, and Tech IV) is a 151 cu in (2.5 L) straight-4 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. Total Duke engine production is estimated to be between 3.8 and 4.2 million units.
At the time of the 1973 oil crisis the only engines Pontiac built were 350 cu in (5.7 L), 400 cu in (6.6 L), and 455 cu in (7.5 L) versions of 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. The engineers considered developing smaller displacement versions of the existing V8, a V6 derived from the V8, a V4 derived from the V8, and an inline-four derived from one 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. The 'all-new' claim was partially marketing terminology as many of the external parts, such as the distributor, water pump, manifolds, and carburetor were taken directly from the earlier Chevrolet 4-cylinder engine some with small dimensional changes making them non–interchangeable. Further confusion is due to the bare blocks looking visually nearly identical even though almost none of the internal parts are interchangeable between the two engine series. Borrowing parts like this greatly reduced development, tooling, and production time and costs. The early few years of the Iron Duke are more closely related to the earlier Chevrolet 4-cylinder than the later versions with numerous design changes such as fuel injection, flat belt accessory drive, cross flow heads, and balance shafts. Interestingly, the water pump from the late production years will bolt onto a first year production 1961 Chevrolet 151 4-cylinder engine, although designed for reverse rotation.
The development team's design goals were to minimize noise and vibration while maximizing durability, drivability, fuel economy, and "usable" power at lower engine speeds. They began by analyzing other four-cylinder engines in production at General Motors at the time, and they found that GM do Brasil's 151 cu in (2.5 L) version of the Chevrolet 153 cu in four-cylinder—with a shorter 3-inch (76 mm) stroke and longer 6-inch (150 mm) connecting rods—had significantly reduced secondary vibration as compared to the original Chevrolet design and the newer 2.3-liter four-cylinder from the Chevrolet Vega. This obviated the need for counter-rotating balance shafts, which would have increased the weight, complexity, and cost of the engine. Despite sharing the same bore, stroke, and cylinder spacing as the Brazilian engine, the majority of parts are not interchangeable.
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.
To maximize durability the engine block was made of cast iron with five main bearings, 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 belt-driven 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.
A two-stage, two-barrel carburetor with electric 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 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.
The Iron Duke's first applications were in the 1977 Astre and Sunbird subcompact cars, replacing the 2.3-liter 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. Peak power increased to 90 hp.
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