Pontiac V8 engine

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Pontiac V8 engine
1965 Pontiac GTO Tri-Power 389 Trophy V8
Overview
Manufacturer	Pontiac (General Motors)
Also called	Strato Streak
Production	1955–1981 Pontiac Assembly (engine block and heads) Saginaw Metal Casting Operations
Layout
Configuration	90° V8
Displacement	265 cu in (4.3 L) 287 cu in (4.7 L) 301 cu in (4.9 L) 303 cu in (5.0 L) 317 cu in (5.2 L) 326 cu in (5.3 L) 347 cu in (5.7 L) 350 cu in (5.7 L) 370 cu in (6.1 L) 389 cu in (6.4 L) 400 cu in (6.6 L) 421 cu in (6.9 L) 428 cu in (7.0 L) 455 cu in (7.5 L)
Cylinder bore	3.72 in (94.5 mm) 3+3⁄4 in (95.3 mm) 3.78 in (96 mm) 3+7⁄8 in (98.4 mm) 3.9375 in (100.01 mm) 4 in (101.6 mm) 4+1⁄16 in (103.2 mm) 4+3⁄32 in (104 mm) 4.121 in (104.7 mm) 4.1525 in (105.47 mm) 4.342 in (110.3 mm)
Piston stroke	2.84 in (72.1 mm) 3 in (76.2 mm) 3+1⁄4 in (82.6 mm) 3.5625 in (90.49 mm)
Block material	Cast iron Aluminum (427 Hemi SOHC)
Head material	Cast iron
Valvetrain	OHV 2 valves x cyl.
Compression ratio	7.9:1, 8.0:1, 8.4:1, 8.5:1, 8.6:1, 8.9:1, 10.0:1, 10.25:1, 10.5:1, 10.75:1, 11.0:1
RPM range
Redline	varies
Combustion
Turbocharger	Garrett TBO-305 (in 301)
Fuel system	Rochester or Carter Carburetors Fuel injection
Fuel type	Gasoline
Cooling system	Water-cooled
Output
Power output	120–310 hp (89–231 kW) SAE (370 bhp)
Torque output	245–500 lb⋅ft (332–678 N⋅m)
Dimensions
Dry weight	550 to 650 lb (250 to 290 kg)

The Pontiac V8 engine is a family of overhead valve 90° V8 engines manufactured by the Pontiac Division of General Motors Corporation between 1955 and 1981. The engine featured a cast iron block and head and 2 valves per cylinder. Engine block and cylinder heads were cast at Saginaw Metal Casting Operations then assembled at Tonawanda Engine before delivery to Pontiac Assembly for installation.

Initially marketed as a 287 cu in (4.7 L), it went on to be manufactured in displacements between 265 cu in (4.3 L) and 455 cu in (7.5 L) in carburated, fuel injected, and turbocharged versions. In the 1960s the popular 389 cu in (6.4 L) version, which had helped establish the Pontiac GTO as a premier muscle car, was cut in half to produce an unusual, high-torque inline four economy engine, the Trophy 4.

Unusual for a major automaker, Pontiac did not have the customary "small-block" and "big-block" engine families common to other GM divisions, Ford, and Chrysler. Effectively, Pontiac's V8s were all small blocks, sharing the same connecting rod length 6.625 in (168.3 mm) (except for the later short deck 301 and 265 produced in the late '70s and early '80s before Pontiac adopted universal GM engines).

The V8 was finally phased out in 1981, replaced by a GM "corporate engines" such as the Chevrolet 305 cu in small block V8.

History[]

Pre-development[]

Pontiac began as a "companion make" to the Oakland division of the General Motors line of automobiles in 1926. Pontiac successfully competed against more-expensive inline four-cylinder models with their inline flathead six-cylinder engines. After outselling Oakland, Pontiac became the sole survivor of the two by 1932. In addition to the inline 6, Pontiac used the Oakland V8 for one year, 1932, debuting the Pontiac straight-8 engine in 1933. The two inline engines were used through 1954, when Pontiac unveiled its OHV Strato Streak V8 in 1955. The development of this V8 dates back to 1946, when engineers began considering new engine designs for postwar cars. They came up with a 269-cubic-inch (4.4 L) L-head design. Pontiac engineers tested their 269 cu in (4.4 L) V8 in 1949 or 1950 against an OHV Oldsmobile Rocket V8 303 cu in (5.0 L) downsized to 270 cu in (4.4 L). The results showed Pontiac that an L-head simply couldn't compete with an overhead valve engine.

Despite their work, the division's conservative management saw no immediate need to replace the Pontiac Straight-8 until later in the 1950s. The concept car Pontiac Strato-Streak was used to introduce the V8 and in later years the engine was installed in Pontiac products.

Development[]

By 1949 work on a 287 cu in (4.7 L) OHV V8 had begun, but moved along slowly. When Robert Critchfield took over as general manager in 1952, he launched an ambitious plan to move Pontiac into the upscale, mid-range market occupied by Oldsmobile, and that demanded V8 power. A new engine was fast-tracked, its relatively late start allowing it to take advantage of developments proven in the Oldsmobile V8 and Cadillac V8. As a result, it was remarkably free of teething problems. During 1951–1952, Pontiac had 23 287 cu in (4.7 L) V8-equipped 1953 model production prototypes running tests on the GM proving grounds. Pontiac planned to produce the 1953 models with the V8, but Buick and Oldsmobile appealed to GM management and earned a 2-year delay.

The main innovation of the Pontiac engine was reverse-flow cooling and the stamped rocker-arm system, which had been devised by Pontiac engineer Clayton Leach in 1948. At the request of Ed Cole, general manager of Chevrolet, the layout was also used by the Chevrolet V8 released in 1955, an exception to the customary GM policy of allowing a division one year of exclusive use of an internally developed advance.

Displacement began at 287-cubic-inch (4.7 L) and grew as large as 455-cubic-inch (7.5 L) by 1970. Pontiac continued to manufacture its own engines, distinct from Buick, Cadillac, Chevrolet, or Oldsmobile, until 1981. Pontiac engines were used in its U.S.-market cars; Canadian-built Pontiac automobiles generally used Chevrolet engines. From 1955 through 1959, the Pontiac V8 was also used in some GMC pick-up trucks. Federal emissions standards and the drive towards "corporate" engines shared among all GM divisions led to the progressive demise of the Pontiac V8 through the late 1970s. The last "true" Pontiac V8s, a 265 and 301 cu in (4.3 and 4.9 L), ended production in early 1981.

Design[]

The 1955-up Pontiac V8 that finally reached the public was an overhead valve engine with cast iron cylinder heads and block and wedge-shaped combustion chambers. An innovative design feature was mounting the rocker arms on ball pivots on studs set into the cylinder head, rather than using a separate rocker shaft. Along with being cheaper to build, this allowed more consistent valve action with less weight than a conventional shaft.

All Pontiac V8s from 1955 to 1959 were reverse cooled, known as the "gusher" cooling system. It was removed from the design for the 1960 model year because designers moved the generator and the power steering pump from atop the front of the engine down to the front of the heads to accommodate a lower hoodline. However, the 1959 389 engines had the generator in front of the heads with reverse flow cooling still in use. This suggests that the cost of the reverse cooling was the reason for the change to "equa-flow" cooling.^{[citation needed]}

Pontiac differed from other GM Divisions and most other manufacturers in producing only a single small block V8, rather than adding a larger big block to its line-up. The external dimensions of all their V8s, from 326–455 cu in (5.3–7.5 L) were the same. Engine displacement is a function of bore and stroke. Pontiac's V8s share the same 6.625 in (168.3 mm) connecting rod length, with the exceptions of the later short deck 301, 265, and 303 Ram Air V.

Most Pontiac V8s had an overall length (to the edge of the water pump pulley) of 28.25 in (718 mm), an overall width of 27 in (690 mm), and a height (not including air cleaner) of 31 in (790 mm)× 686 mm × 787 mm^{[clarification needed]}. Dry weight ranged from 590 to 650 pounds (270 to 290 kg), depending on displacement and year. Most Pontiac engines were painted light blue. The 1958 370" engine and the 1959–60 389 version was named the "Tempest" V-8 and changed in 61 to the "Trophy" V8. Pontiac in the 1950s was one of a few US manufacturers that did not regularly identify their engine names and sizes with air-cleaner or valve-cover decals.

Small-journal engines:1955-1981[]

287[]

The V8 engine was introduced for the 1955 model year as the "Strato Streak". Not long before the model year introduction, Pontiac management decided that the entire line would be V8-powered. This was based on results of over 1 million test miles, which was unheard of at the time. The 287 was an "oversquare" engine with a bore and stroke of 3+3⁄4 in × 3+1⁄4 in (95.3 mm × 82.6 mm), for a total displacement of 287.2 cu in (4.7 L). Compression ratio was a modest 8.00:1, with valve diameters of 1.781 in (45.2 mm) (intake) and 1+1⁄2 in (38 mm) (exhaust). It was rated 180 hp (134 kW) @ 4600 rpm and 264 lb⋅ft (358 N⋅m) @ 2400 rpm with a two-barrel carburetor, 200 hp (149 kW) @ 4600 rpm and 278 lb⋅ft (377 N⋅m) @ 2800 rpm with the four-barrel carburetor.

317[]

For 1956 the V8 was bored out to 3.9375 in (100.01 mm), increasing displacement to 316.6 cu in (5.2 L). It was offered in the following forms:

(with manual transmission)

• Two-barrel carburetor, 7.9:1 compression, 192 hp (143 kW) @ 4400 rpm, 297 lb⋅ft (403 N⋅m) @ 2800 rpm
• Four-barrel carburetor, 8.9:1 compression, 216 hp (161 kW) @ 4800 rpm, 315 lb⋅ft (427 N⋅m) @ 2800 rpm

(with Hydramatic)

• Two-barrel carburetor, 8.9:1 compression, 205 hp (153 kW) @ 4600 rpm, 294 lb⋅ft (399 N⋅m) @ 2600 rpm
• Four-barrel carburetor, 8.9:1 compression, 227 hp (169 kW) @ 4800 rpm, 312 lb⋅ft (423 N⋅m) @ 3000 rpm
• Two four-barrel carburetors, 10.5:1 compression, 285 hp (213 kW) @ 5100 rpm, 330 lb⋅ft (447 N⋅m) @ 2600 rpm.

347[]

For 1957 the V8's stroke was increased to 3.5625 in (90.49 mm), for a displacement of 347 cu in (5.7 L). For the first time, Pontiac offered Tri-Power, three two-barrel carburetors with a sequential linkage (replacing the previous dual-quad set-up). Power ratings increased accordingly:

(with manual transmission)

• Two-barrel carburetor, 8.5:1 compression, 227 hp (169 kW) @ 4600 rpm, 333 lb⋅ft (451 N⋅m) @ 2300 rpm
• Four-barrel carburetor, 10:1 compression, 244 hp (182 kW) @ 4800 rpm, 350 lb⋅ft (475 N⋅m) @ 2600 rpm

(with Hydramatic)

• Two-barrel carburetor, 10.0:1 compression, 244 hp (182 kW) @ 4800 rpm, 350 lb⋅ft (475 N⋅m) @ 2600 rpm
• Four-barrel carburetor, 10.25:1 compression, 270 hp (201 kW) @ 4800 rpm, 359 lb⋅ft (487 N⋅m) @ 2900 rpm
• Three two-barrel carburetors, 10.75:1 compression, 290 hp (216 kW) @ 5000 rpm, 375 lb⋅ft (508 N⋅m) @ 2800 rpm.

Several dealer-installed camshafts were optional to increase power further to 317 hp (236 kW). which was seen on the hood of the 1957 Daytona Grand National winning car driven by Cotton Owens.

Standard only for the Pontiac Bonneville was Pontiac's first-ever fuel injection system. A mechanical system built by Rochester, it was similar in principle, but not identical, to the contemporary Chevrolet "fuelie". Pontiac did not release official power ratings for this engine, saying only that it had more than 300 hp (224 kW). Contemporary road tests suggest that it was actually somewhat inferior to the Tri-Power engines, although it did have better fuel economy. Only 630 Bonnevilles were produced for 1957, all of them fuel-injected.

370[]

For 1958 the V8's bore was increased again to 4+1⁄16 in (103.2 mm), increasing displacement to 369.4 cu in (6.1 L). The engine was dubbed the TEMPEST V-8, a nickname it retained until the end of 1960.

The fuel-injected engine became an option on any Pontiac model, carrying a staggering price tag of $500 (almost 15% of the car's base price). It was rated at 310 hp (231 kW) @ 4800 rpm and 400 lb⋅ft (542 N⋅m) @ 3,000 rpm on 10.5:1 compression. Only about 400 were produced before the fuel injection system was quietly dropped.

389[]

For 1959 the V8's stroke was increased to 3+3⁄4 in (95.3 mm), raising displacement to 389 cu in (6.4 L). This was the beginning of factory supplied performance items such as 4 bolt main bearings and windage trays to reduce friction from crankcase oil. The 389 would remain the standard Pontiac V8 engine through 1966, offered in a bewildering variety of outputs ranging from 215 to 368 hp (160 to 274 kW). The 389 was the standard engine for the Pontiac GTO through 1966. Beginning in 1961 the Pontiac V-8 (389 and 421) was dubbed the Trophy V-8, due to its many victories in racing.

Trophy 4[]

Perhaps the most unusual variation of the Pontiac V8 was the 1961-63 Trophy 4, which was a 45-degree inclined 194.43 cu in (3.2 L) inline-4 created from the right bank of the 389 for the debut of the Tempest. With an identical bore and stroke of 4+1⁄16 in (103.2 mm) and 3+3⁄4 in (95.3 mm) it was precisely half the displacement of the 389 and shared numerous parts with the V8,^[1] yet weighed considerably more than half as the engine lower half and block casting were not simply divided down the middle.

326/336[]

In 1963 Pontiac dropped the Buick division built 215 cu. in. aluminum V8 it had offered in the Tempest and replaced it with a small-bore version of the standard 389 cu in (6.4 L) Pontiac V8. It shared the 389's 3+3⁄4 in (95.3 mm) stroke, but its bore was 3.78 in (96.0 mm) for a displacement of 336.66 cu in (5.5 L). It was rated at 250 hp (186 kW) with 8.6:1 compression and 260 hp (194 kW) at 10.25:1 compression. Both used a single two-barrel carburetor. In 1964 when the new "A" body intermediates came out there was a new corporate (GM) engine size limitation to anything less than 330 cu in (5.4 L). and so the 326 bore size was reduced to 3.72 in (94.5 mm), giving a true 326.06 cu in (5.3 L). The 326 subsequently became the optional V8 engine for Tempests, and later the Pontiac Firebird, through 1967 and maintained the 17 degree cylinder head valve angle for its entire production run.

A higher-output four-barrel carburetor version was offered, called the 326 HO (High Output). With higher compression and dual exhaust it produced 280 hp (209 kW) for 1963–1964, and 285 hp (213 kW) for 1965 through 1967, its final year.

400[]

For 1967, Pontiac retired the 389 cu in (6.4 L) and replaced it with the 400 cu in (6,554 cc), a 389 bored-out by +0.06 in (1.5 mm) to a bore and stroke of 4.12 in × 3+3⁄4 in (104.6 mm × 95.3 mm). The 400 remained in production through the 1978 model year, with 1979 cars receiving engines produced the previous year.

In basic 2-barrel form it produced 290 horsepower and 428 ft. pounds of torque in 1968.^[2] This was the engine installed in Pontiac's "executive" line of large cars^[3] and its largest station wagon.

In 1967, the cylinder head design was improved for the 400 4-barrel engine. The valve angle was reduced from 17 degrees to 14 degrees for better breathing. 1967 was the last year for closed-chambered heads. The "670" head was a 1967-only casting, and the only PMD head to have a closed chamber with the new 14 degree valve angle. The 400 2-barrel kept the 17 degree valve angles for '67; starting in '68 all Pontiac V8s went to the 14 degree valve angle. Pontiac went to open-chambered heads in some 1967 models and all 68 and up to improve power, engine breathing and reduce emissions. The valve size increased as well, to 2.11 in (53.6 mm) intake and 1.77 in (45.0 mm) exhaust valves on high-performance heads. Low-performance and two-barrel applications, the standard engine in full-sized Pontiacs, got 1.96 in (49.8 mm) intake and 1.66 in (42.2 mm) exhaust valves and pressed in rocker arm studs.

The four-barrel 400 was a popular performance option for many of Pontiac's cars. When fitted with other high-airflow components, it produced a good balance of low-end torque and higher-RPM power. In the 1968 Pontiac GTO it was given a 10.75:1 compression ratio and tuned to deliver 360 horsepower and 445 foot-pounds of torque.^[2]

350[]

In 1968 the 326 was replaced by the similarly 389-derived 350, which used a 3+7⁄8 in (98.4 mm) bore and 3+3⁄4 in (95.3 mm) stroke for a total displacement of 353.8 cu in (5,798 cc). Like the 326, it was offered in both 2-barrel and 4-barrel versions. In 1968 a 320 hp (239 kW) HO option was offered in the Tempest and Firebird. The 1969 HO 350 HO was equipped with the 400 cu in (6.6 L)'s large valve heads (# 48's) and the 400 HO camshaft and rated at 330 hp (246 kW). In 1974 it was used in the GTO and was rated at 200 hp (149 kW) (net).

303[]

In 1969, Pontiac unveiled its Trans Am model Firebird, and since racing rules required engines of less than 5 L (305.1 cu in), Pontiac unveiled the 303 for racing models only, never available to the public. Bore and stroke were 4.121 in × 2.84 in (104.7 mm × 72.1 mm) 303.63 cu in (4,976 cc). It was rated at 475 hp (354 kW).

301[]

The 301.6 cu in (4.9 L) 301 was offered from 1977 to 1981 and also installed in other GM cars during those years. The 301 had a bore and stroke of 4 in × 3 in (101.6 mm × 76.2 mm). Based in part on designs for the "short deck" 303 cu in (5.0 L) engine designed for the 1970 racing season, it had a shorter deck than the big V8, and used thin-wall castings to reduce weight. The crankshafts were also unique in the fact that they featured only two counter weights instead of the usual five and also featured lightened connecting rod journals. This resulted in a lightweight design weighing less than the Chevrolet small-block V-8. Power output ranged from 135 hp (101 kW) to 170 hp (127 kW). The heads were a new design featuring siamesed intake ports. The short-deck block and different intake ports also required the design of a new intake manifold. The Pontiac 301 EC (Electronic Controls) version offered in 1981 produced 155 hp (116 kW) and 245 lb⋅ft (332 N⋅m), although it's rumored that the actual output was closer to 170 hp (127 kW). The 1980 301 Turbo was rated at 210 hp (157 kW) at 4400 rpm and 345 lb⋅ft (468 N⋅m) @ 2800 rpm. The 1981 301 Turbo gained the electronic controls with an O₂ sensor, feedback ECM and E4ME Quadrajet providing a slight reduction in output to 205 hp (153 kW) and 340 lb⋅ft (461 N⋅m). Although it is much different from the original 1955-vintage Pontiac V-8 powerplant, the 301 has the distinction of being the last true Pontiac V-8 engine, as Pontiac ceased production of these engines effective April 1, 1981.

From 1977 to 1981 there were 4 distinct 301 versions:

• 301 2-barrel (135 hp, 101 kW), (5th digit of the VIN is a "Y")
• 301 4-barrel (150 hp, 112 kW)
• 301 4-barrel 'HO' or 'EC' (170 hp, 127 kW) (with the 5th digit of the VIN being a "W")
• 301 Turbo (210 hp, 157 kW), with the 5th VIN digit being a "T".

For 1981 model year vehicles, the engine codes are the 8th digit of the VIN. The 2-barrel version was last offered in 1979. The 4-barrel version was available from 1978 to 1981 and the Turbo version was available in 1980 and 1981 only.

The 301 Turbo was unique in that it had a beefier block than the 1977–79 versions (which carried on in the non turbo versions in 1980 and 1981), a very mild camshaft with 0.35 in (8.9 mm) lift and 250 degrees gross duration, a 60 psi (4.1 bar) oil pump to ensure adequate oil to the oil-cooled Garrett TBO-305 Turbocharger, a rolled fillet crankshaft, a fully baffled oil pan, and a specific 800 cu ft/min (23 m³/min) Quadrajet carburetor. This had extra-rich "DX" secondary metering rods and a remote vacuum source for the primary metering rod enrichment circuit to allow the Power Enrichment Vacuum Regulator (PEVR) to release the primary metering rods to move to the up position (enrichment) anytime during boosted conditions. This was to ensure there was enough fuel to cool the cast offset dished pistons. Boost was wastegate limited to 9 ± 1 psi (0.621 ± 0.069 bar). The 301 Turbo package mandated air conditioning, THM350 (sometimes referred to as the CBC350 in various literature) non-lockup automatic transmission (THM350C lockup in 1981 Trans Ams), and 3.08 rear axle gearing. The 301 Turbo was limited to Trans Am and Formula Firebird production only, although some literature has indicated that the 301 Turbo may have found its way into the Chevrolet Camaro Z28. GM's parts books do list the turbo engine for the Camaro.

301:Naturally Aspirated

• 1977-1981 Pontiac Bonneville
• 1977-1981 Pontiac Catalina
• 1977-1981 Pontiac Firebird
• 1977-1981 Pontiac Grand Prix
• 1977-1981 Pontiac LeMans
• 1977-1981 Pontiac Parisienne
• 1978-1980 Pontiac Grand Am
• 1978-1981

301:Turbo

• 1980-1981 Pontiac Firebird Trans Am

265[]

Based on the same short-deck as the 301, the "LS 5" 265.1 cu in (4.3 L) was offered only in 1980 and 1981, and featured a smaller bore of 3+3⁄4 in (95.3 mm) coupled with the same 3 in (76.2 mm) stroke of the 301 (same bore and stroke used by Chevrolet when the first small block motor was introduced in 1955). It produced 120 hp (89 kW) After 1981, the Pontiac V8 was replaced entirely by the GM "corporate" V8's from Chevrolet and Oldsmobile.

Applications:

• 1980-1981 Pontiac Bonneville
• 1980-1981 Pontiac Catalina
• 1980-1981 Pontiac Firebird
• 1980-1981 Pontiac Grand Prix
• 1980-1981 Pontiac LeMans
• 1980-1981 Pontiac Parisienne
• 1980-1981 Buick Century
• 1980-1981 Buick Regal
• 1980 Oldsmobile 88

Large-journal engines:1961-1976[]

421[]

The 421.19 cu in (6.9 L) was introduced in 1961 as a dealer-installed Super Duty option. Unlike previous enlargements of Pontiac V8s, it did not replace the 389. The first of the "big journal" Pontiac V8s, it had a bore and stroke of 4+3⁄32 in × 4 in (104.0 mm × 101.6 mm) and came with dual four-barrel carburetors. It featured 3+1⁄4 in (82.6 mm) main journals (which the legendary Smokey Yunick reputedly left Pontiac's engineering department over). The 421 SD became factory installed in 1962 and in 1963 a street version became available from the factory with a dual four-barrel or three two-barrel Tri-Power carburetion. Modified versions of this engine were extensively used in NASCAR stock car racing and drag racing competition. The premier SD 421 cylinder head was the late 1962-early 1963 casting #9771980 aka "980", featuring a larger 11.3 cu in (185 cc) intake port volume, flowing 230 cu ft/min (6.5 m³/min) @ 28 in (710 mm).

The 421 also marked the end of the option for a forged-steel crankshaft. The Armasteel cast crankshaft was the standard hardened cast-iron crankshaft used throughout the entire Pontiac V-8 line until 1967. "Armasteel" referred to its "locking ball" cast-iron,^{[citation needed]} as opposed to the "flaking" type found in other engines. In 1967, Pontiac out of concerns the public misunderstood the engineering terms, went to a nodular cast iron crankshaft, which they used until 1975.

428[]

In 1967 the 421 was enlarged to 426.61 cu in (7.0 L) by increasing its bore to 4.12 in (104.6 mm). Both Chevy and Ford had 427 cu in performance engines, so Pontiac simply referred to its 427 as a 428 to one-up them. It retained the 421's 4 in (101.6 mm) stroke and 3+1⁄4 in (82.6 mm) main journal.

Offered from 1967 to 1969, it produced 360 and 376 hp (268 and 280 kW) in 1967, 375 and 390 hp (280 and 291 kW) in 1968 and 360, 370 and 390 hp (268, 276 and 291 kW) in 1969. The crankshaft in the 428 had a "N" cast on them (designating nodular steel) as opposed to the 421's Armasteel. In 1969, Pontiac also used a revised crankshaft out of a Pearlitic malleable-iron, although it still used the "N" casting letter. This new material had stronger alloys in the iron. All 428 cylinder heads received the 14 degree valve angle, closed chamber only in 67 and open chamber 68 and up.

The 428 was factory installed in large cars only. However, a few dealers would offer them in the GTO or Firebird and do their own installations.^{[citation needed]} It was replaced by the 455 for the 1970 model year.

455[]

The 428 was increased to 456.12 cu in (7,474 cc) in 1970. Again, its bore was expanded, this time 0.03 in (0.76 mm) to 4.1525 in (105.47 mm). The 4.21-inch (106.9 mm) stroke remained the same.^[4] It was rated at 360 hp (268 kW), but the Grand Prix with the same specifications^{[citation needed]} was rated at 370 hp (276 kW).

The horsepower ratings of this era were often dubious, with engines rated higher or lower in output for advertising, political, or insurance purposes.^{[citation needed]} Though listed as slightly less powerful than some high-performance iterations of the 400 (such as the 366 hp (273 kW) Ram-Air), the 455 had 500 lb⋅ft (678 N⋅m) of torque, 55 more lb⋅ft (75 N⋅m).

The engine was available in all full-size Pontiacs. An HO version could be ordered in the GTO, as GM had lifted its restrictions on offering engines larger than 400 cu in (6.6 L) in mid-sized cars (resulting in the 454 (7.44) Chevrolet Chevelle, 455 (7.5) Buick Gran Sport, and 455 (7.5) Oldsmobile 442).

For 1971, Pontiac introduced another High Output (HO) version with standard internal parts, a reinforced block with four-bolt main bearing caps, and improved cylinder head design with 1⁄8-inch taller (3.2 mm) intake ports and special round exhaust ports for better breathing, yet still making just 335 hp (250 kW) gross (or 310 hp (231 kW) in the more accurate SAE Net system). Standard in the Firebird Trans Am, it was still a rare engine.

In 1973 a further refined and even stronger but less powerful version, the Super Duty (SD) engine, was introduced with 310 hp (231 kW) using a similar camshaft specifications to the Ram Air IV 400. The 455 SD used round-port cylinder heads similar to those used on the 1971 and 1972 455 HO, with specific "LS-2" intake and cast-iron exhaust header manifolds. Still, it was the strongest American engine offered that year. Its power was achieved through bending of EPA emissions-testing procedures,^{[citation needed]} which led engineers to de-tune the engine to 290 hp (216 kW) in order to comply (via a camshaft change to the same profile used in the early RA III 400 engines for mid-1973 and 1974), after which point it was discontinued.

An evolution of the RA IV and H.O. designs, the 455 SD was a much improved engine. In addition to the more refined cylinder heads, block casting reinforcements in the lifter galley and main bearing oil pan rail area, it had forged connecting rods with larger 7⁄16-inch-diameter (11 mm) bolts. Made with a provision for dry sump oiling, it truly was a racing engine, detuned for use in passenger cars.

The 455 was used through 1976 when it, as with many other large displacement engines, was discontinued as manufacturers moved to smaller, more efficient models, even in their full size car lines.

HO engines[]

326 HO[]

A higher-output version was offered, called the 326 HO (High Output). It had a four-barrel carburetor, dual exhaust, and higher compression, and was good for 280 hp (209 kW) for 1963–1964, and 285 hp (213 kW) for 1965 - 1966 and the final year, 1967.

350 HO[]

In 1968, there was also a 350 "HO" which had increased power with the addition of higher compression #18 heads (#17 and #46 were the most common 2-barrel heads), a four-barrel carburetor and matching intake that was also used on the 400 and 428 engines. There was also the addition of dual exhaust, and in the case of a stick shift car, a slightly more aggressive cam.

In 1969 the 350 HO was upgraded again with the addition of the 400 HO cam, commonly referred to by Pontiac hobbyists as the 068 cam. Also added was the #48 casting number heads with a 68 cc (4.15 cu in) chamber for higher compression, along with larger 2.11 and 1.77 in (54 and 45 mm) valves. Free-flowing exhaust manifolds from the 400 RamAir were used late in the model year. This was underrated at 330 hp (246 kW). Many of GM's other divisions' 350's like Chevrolet, Buick and Oldsmobile and even the base SS396 were handily beaten by this little 350 "High Output" (HO) Pontiac.^{[citation needed]}

Basically a 350 with 400 heads to match the pistons, the 350 H.O. may have been one of the most overlooked high-performance engines of the era,^{[citation needed]} ignored by buyers of larger 400 engines in spite of its exceptional performance.

400 HO[]

This engine was first offered in 1967 as the third engine in the GTO and Firebird line (after the 400 2-barrel and the base 400)....It produced 360 bhp (268 kW; 365 PS), and had the cast iron headers. The camshaft was the HO cam with 288/301 duration. It was the top of the line engine until the 400 Ram Air was introduced later in the year. This engine was offered as an option in 1967 thru 1970. For 1967 only Pontiac called this engine the Quadra-Power 400. It was renamed 400 HO for 1968.

400 T/A 6.6[]

In 1977 the 400-cubic-inch (6.6 L) T/A 6.6, (RPO code W72) was created to fulfill the vacuum of the lackluster 76 455 HO, with improved flow cyl "6X" casting heads borrowed from the 350 yielding higher compression ratio, specific camshaft and 3.23 gearing it made 200 hp (203 PS; 149 kW) at 3600 rpm and 325 lb⋅ft (441 N⋅m) of torque at 3600 rpm. The base 400 engines in 1977-78 produced 180 hp (134 kW). In 1978 a new dual muffler exhaust was added making 220 hp (164 kW) (net) as published by Pontiac, and provided the Trans Am and Formula Firebird with a breath of new life after some dismal performance years. The 4-speed manual transmission was also available behind the 400 T/A 6.6. Car & Driver magazine named the 400 T/A 6.6 Trans Am with its WS6 suspension package the best-handling American car in 1979.

The 400 T/A 6.6 did not live long however, emission standards and fuel economy restrictions for 1980 model year doomed the powerplant. The 301 Turbo replaced the 400 T/A 6.6 in 1980, disappointing potential customers who were just getting excited about performance returning to Pontiac.^{[citation needed]} The 400 T/A 6.6 Trans AM was the last of the performance cars available with the manual transmission, also yet another disappointment to potential customers. All 400 engines for 1979 were W72 versions and were last produced in 1978, after which time the tooling was dismantled. Some engines in 1979 vehicles may have been cast as early as 1977. W72 versions had chrome valve covers, base 400 versions had painted covers.

The hood scoop decal distinguished which version of the engine was in the vehicle. The W72 cars had "T/A 6.6". The 185 hp (138 kW) 403 cu in (6.6 L) Oldsmobile powered cars as well as the base 400 cars had "6.6 LITRE" on the scoop. It has often been mistakenly thought that in 1977-79 ONLY the "T/A" prefix on the hoodscoop denoted that it was a Pontiac sourced engine, and those ending in Litre were non-Pontiac sourced Olds 403 were 6.6 litre decals. (Note: In 1980–81, this would change as the 5.0 L (305 cu in) Chevrolet produced engine was offered and had "5.0 LITRE" on the hood scoop). 1977 was the first year for the litre designation on the scoop, prior to that, it was shown in cubic inches. According to the June 2019 issue of Musclecar Review magazine, during period dyno testing, the National Hot Rod Association (NHRA) rated this Pontiac W72 400 T/A 6.6 engine at 260 to 280 net horsepower instead of the 220 hp rating published by Pontiac.

421 HO[]

First offered as an option in 1963, the 421 HO came in a 4-barrel engine of 320 hp (239 kW) and one Tri-Power H-O version with a hotter cam and efficient iron exhaust manifolds and rated at 370 hp (276 kW). Pontiac offered this to the public as a streetable version of the 421 SD. The engine came with 543797 (4-barrel) and 9770716 heads for the tripower and special exhaust manifolds and a 7H cam with 292deg. intake duration and later 1964 L with 288deg intake essentially the same as the 068 cam. #9770716 aka "716" heads featured a 170cc intake port volume, and were considered a milder "street" version of the vaunted SD421 Super Duty heads. These same heads were also used on the 1964 GTO 389 tri-power engines. By 1965 and 1966 the same combinations would be rated at 338 hp (252 kW) for the 4bbl and the two Tri-Power versions would be rated at 356 hp (265 kW) and the H-O version at 376 hp (280 kW).

428 HO[]

This engine was first offered in 1967 as the top engine option in full-size Pontiacs. It was rated at 376 bhp in 1967 and 390 bhp in 1968 and 1969. For 1967 only Pontiac called this engine the Quadra-Power 428. It was renamed 428 HO for 1968.

455 HO[]

1970

The 455 HO designation made its debut in 1970; Rated at 360 or 370 hp (268 or 276 kW) (depending on which vehicle it was installed into) & 500 lb⋅ft (678 N⋅m) of torque, it differed from the regular full sized car 455 by large valve heads with smaller combustion chambers, and a larger camshaft.

The 1970 '455 HO' was a conventional "D" port engine – to simplify things, it was a late model year offering which was truly a 'High Output' version of the 455 offered from the onset of the model year in all Pontiacs full sized cars.

1971

The "455 HO" moniker took on a whole new meaning with the introduction of the 1971 model year;

Intended as a low compression progression from the previous years Ram Air IV engine, all 1971 455 HO engines used a heavy duty 4 bolt main block, round port cylinder heads (casting #197; with 8.4: compression), "Ram Air" style exhaust manifolds, and a two-part aluminum intake manifold.

The 1971 Pontiac 455 HO was Pontiac's first engine to receive a special 800 cu ft/min (23 m³/min) Rochester Quadra-jet carburetor with specific jetting.

The 1971 455 HO was rated at 335 hp (250 kW) @ 4,800 rpm and 480 lb⋅ft (651 N⋅m) of torque @ 3,200 rpm (gross).

The 1971 455 HO was available in the Firebird (Formula and Trans Am), and the GTO.

1972

The 455 HO moniker was again carried over, this time as a near-exact repeat of the 1971 offering, the only changes were the carburetors (they used a conventional 750 cu ft/min (21 m³/min) unit this year), and the head castings (casting #7F6).

According to GM mandates horsepower was now rated in net figures as opposed to gross, so on paper the 1972 455 HO appeared to have a significant drop in power, but in fact it was very much the same engine, and performance figures reveal this to be true.

The 1972 455 HO was rated at 300 hp (224 kW) @ 4,000 rpm and 415 lb⋅ft (563 N⋅m) @ 3,200 rpm.

The 1972 455 HO was available in the Firebird (Formula and Trans Am), and the GTO.

1975

After the 1974 SD455 was dropped the 1975 Firebird's top performance engine was an 'L78' Pontiac 400 cu in (6.6 L).

Pontiac still offered the regular 455 (RPO L75) in its full sized cars, and after some public outcry a "455 HO" package was offered for the Firebird's top of the line Trans Am model.

The 1975 455 HO was not simply an engine, but instead a package, this package consisted of:

• 455 'L75' engine
• BorgWarner 'T-10' four speed manual transmission
• 3.23:1 positraction differential
• "455 HO" callouts on the 'shaker' hood scoop

The 1975 455 'L75' was rated for 200 hp (149 kW) @ 3,500 rpm (net).

The 455 HO package was only available to late model year Pontiac Firebird Trans Am's.

The 1975 455 HO package received some negative press/reviews as some buyers expected to see a return of the 1971-1972 engine.

1976

The 1975 late model year "455 HO" package was carried forward and offered again on the 1976 Trans Am - but for this year the "HO" was dropped as a result of the negative press/reviews from the model year prior.

Ordering the 'L75' 455 in the Pontiac Firebird Trans Am included the same packaged items as the previous model year, with the sole exception that the 'shaker' hood scoop call out now simply read "455".

Model year 1976 was the last year that Pontiac produced the 455 cu in (7.5 L) engine, and the final year of any 455 HO engine or package.

301 HO[]

While not "high-output" fashion by the 1960s and 1970s standards and no "HO" moniker on the shaker hood scoop, the 301 did end up with a HO "performance" version, yielding 170 hp (127 kW) with only 4.9 L (299 cu in) for the 1980–1981 model years. The 1981 edition engine was officially called the 301-EC [EC standing for Electronic Controls] in the 1981 GM factory service manual. The 301 HO was the base Trans AM engine in 1980 and 1981.

The modifications over the standard 301 4-barrel were designated the 301 Turbo "301T" block. This included the ESC (Electronic Spark Control) distributor and controller borrowed from the 301 Turbo, which allowed for higher timing without the penalty of engine damaging pinging or preignition. A large 4 in (101.6 mm) ram air duct to the air cleaner, specific carburetor calibration for the 301 HO, 60 psi oil pump, and cam similar in grind to the 220 hp (164 kW) 400 from the 1978–1979 model year were also included. Unfortunately, there were no improvements in the casting number "01" small-valve high-velocity heads, which would have yielded greater improvements in power.

Ram Air[]

The beginnings of Pontiac's iconic Ram Air dynasty began during the 1965 model year. The GTO's new hood scoop design, with the inlets centrally located and mounted above the carburetor, provided the opportunity for experimentation. Royal Pontiac developed the prototype of the package on their 1965 GTO drag car and Pontiac picked up the idea and in August of 1965 Pontiac offered the new Fresh Air package to dealers consisting of the parts and instructions needed to make the hood scoop functional, including the metal tub to mount to the carburetors and rubber gasket to seal it to the underside of the hood. The Fresh Air package continued into the 1966 model year.

Around January of 1966 Pontiac took the next step and began offering as a factory option the XS-code engine. It included a new camshaft with duration increased from 288/302 (No. 068) to 301/313 (No. 744) and a new valve spring package with dampers to positively control valve action. Valve lift stayed at just over 0.400-inch with 1.5:1-ratio rocker arms. The tri-power equipped XS-code 389 was shipped with the Ram Air pan in the trunk, and the dealer had to fit it and cut out the underside of the hood scoop to make it functional. The XS-code 389 was still rated at 360 bhp at 5,200 rpm, same as the more common WS-coded Tri-Power 389, but performance was noticeably improved on acceleration runs. Pontiac engine production records report that 190 XS-code 389 engines were built during the 1966 model year. Whether all were installed in GTOs is unknown.

Ram Air I[]

While not officially called the Ram Air I when it was issued,^{[citation needed]} it was the first in a series of Ram Air V8 engines from Pontiac. Hewing to GM's standing edict limiting engine size to 400 cu in for its midsize and smaller cars, the 360 hp (268 kW) (underrated),^{[citation needed]} Ram Air I was the most powerful and advanced option available in the 1967 GTO and Firebird. Its cast "670" heads had taller valve spring heights than the standard D-port heads, and the only 14-degree valve angle closed combustion chamber making these heads unique. It featured the "744" 301/313 camshaft, which offered more duration and overlap than the "HO". Along with the HO it also had Pontiac's famous cast-iron "headers", which were much better at reducing backpressure than the regular manifolds. None of Pontiac's Ram Air engines actually enjoyed any true ram air effect. The inlets were all well within the boundary layer that exists close to the surface, so all of these systems would more accurately be described as "outside air induction" systems, benefiting from the intake of cooler, and thus denser, outside air versus the comparatively hotter and less dense air under the car's hood.

Ram Air II[]

The 1968 Ram Air II remained at 400 cu. in., again available only in the GTO and Firebird. It was factory rated at 366 hp at 5,400 RPM and 445 lbs.ft. of torque at 3,800 RPM in the GTO, and 340 HORSEPOWER at 5,300 RPM and 430-lb.ft. of torque at 3,600 RPM in the Firebird, with only a small throttle restrictor tab on the Firebird being different.^{[citation needed]} It was the first engine that incorporated Pontiac's round-port head design in a production vehicle, however the intake port was the same as other D-port heads, leaving a head which exhaust port could nearly match the intake at high valve lifts. The Ram Air II also incorporated the first computer-designed camshaft. This camshaft sported a 308-/320-degree duration with 0.47-inch (12 mm) lift. This same camshaft was also used in Pontiac's 1969–1970 RA IV production cars. However, the RA II was limited to a 1.50:1 rocker ratio, while the RA IV used a 1.65:1 ratio, which yielded significantly greater total lift and, therefore, superior flow and power.^{[citation needed]}

Ram Air III[]

The Ram Air 400 was once again an option on 1969-70 GTO and Firebird Trans Am, and the standard engine with the optional GTO "The Judge" package. Today known colloquially as the "Ram Air III", though never called that by Pontiac, it was the same engine as the '67-'68 400 HO^[5] and identical to the 1969 400 Ram Air, as it was called as it was then fitted with a Ram Air outside air induction system. It used the "744" camshaft (301-313) in the earlier manual trans versions, later downgraded to the "068" version, and the 288/302 duration cam with automatic transmission. It was rated at 366 bhp (273 kW) (gross) in the GTO version. It later became known colloquially as the "Ram Air III" but Pontiac never used that name. Like previous generations of Ram Airs, it used Pontiac's special cast-iron "headers". It had 2-bolt main bearing caps in 1969, but went to a block similar to the Ram Air IV's in 1969 that was drilled for 4-bolt main bearing caps (but used a cast crank and cast rods). In 1970 the casting number #9799914 Ram Air 400 4-bolt main block also used the 4-bolt main caps on Ram Air applications.

Ram Air IV[]

The Ram Air IV replaced the Ram Air II in 1969. It was called the Ram Air IV due to the planned use of four air inlets. Though production cars only got the two hood air inlets, the name was retained. All 1968–69 #9792506 Ram Air 400 blocks have 4-bolt caps. The Ram Air IV used the RA II's camshaft but lift in the RA IV was increased to 0.52 in (13 mm) thanks to the use of 1.65 ratio rocker arms (vs 1.50). The RA IV heads had 1/8" taller intake ports, larger intake port volume with more airflow, yet shared the Ram Air II round exhaust ports. In addition, a shallower spherical-wedge combustion chamber moved the tuliped valve heads .040" closer to the piston at TDC, improving mixture draw considerably during the intake stroke. The RA IV also used a lightweight aluminum intake-manifold that produced a weight savings of 10–15 lb (4.5–6.8 kg). From 1969 though 1970, the RA IV was available in both A-Body (GTO/Judge) and F-body (Firebird/Trans Am) form. While 1969–70 A-body RA IV production was low (1517) only 102 RA IV Firebirds and 55 Trans Ams were built in 1969. RA IV Trans Am production jumped to 88 units built in 1970. After RA IV production ended, Pontiac continued using its round-port cylinder-head design for 1971-'72 on the 455 HO. However, by this time compression had dramatically dropped off, marking the beginning of the end of the muscle car era.

Ram Air V[]

In 1969 Pontiac created four versions of the Ram Air V engine: a 303 cu in (5.0 L) short deck version for SCCA Trans-Am racing, a 366 cu in (6.0 L) variant for NASCAR, a 400 cu in (6.6 L) version for street use in GTOs and Firebirds, as well as a 428 cu in (7.0 L) adaptation for drag racing.^[6] The cylinder head design is similar to the Ford FE tunnel-port head used in the GT40 and Can-Am series racing. So large are the intake ports that the pushrods run through the center of each port via pressed-in tubes, in addition to streamlined airfoils over the tubes themselves to improve port shape, and increase flow velocity. The 303 had shorter connecting rods, smaller 2.5 in (64 mm) journals and a solid lifter version of the Ram Air IV camshaft. It shared the 4.121 in (104.7 mm) bore of the 400, but with a 2.84 in (72.1 mm) stroke for a displacement of 303 cu in (5.0 L). The short deck engine weighed about 40 lb (18 kg) less than the other variants and had an 8000 rpm redline. Pontiac's SCCA Trans-Am program was promising, with race-ready engines producing 475 hp (354 kW) to 525 hp (391 kW), however the series’ General Competition Rules required the manufacturer to produce no less than 250 vehicles with the 303. Plans were made to produce Firebirds and GTOs with advertised ratings of 355 hp (265 kW) and 375 hp (280 kW) respectively but concerns about emissions, the response of the automobile safety lobby, and the warranty implications of a high-revving street engine led to cancellation of the program.^{[why?][citation needed]} T

The total number of Ram Air V engines produced is not positively known and a handful of Ram Air V 303's may have made their way onto the Pontiac Firebird Trans Am assembly line.^{[citation needed]} Only about 25 303 cu in (5.0 L) engines were produced and about a dozen 428s and 366s. More 400 cu in (6.6 L) engines were produced by Pontiac than the other versions - estimates range from 80 to 200 units. Quite a few 400s were dealer installed.^[6]

Parts for Ram Air V engines are not readily available. The cylinder heads on the 400 CID version had an intake port volume of 290 cc (17.70 cu in), nearly twice the size of a typical standard D-port Pontiac head - and flowed in the area of 315 cu ft/min (8.9 m³/min) @ 0.8 in (20 mm) valve lift; in the realm of the NASCAR-dominating Chrysler 426 Hemi.^{[citation needed]}

Super Dutys[]

SD421[]

The 421SD was available in 1961 as a dealer option or over the counter then in 62 and 63 from the factory, and was fitted with a list of internal modifications designed solely to withstand the abuse of drag racing. Cam was a #541596 McKellar No. 10 with 308/320 degrees of duration and 0.445 / 0.447-inch lift (11.3 / 11.4 mm) with 1.65:1-ratio rocker arms and solid lifters, special #529238 forged-steel connecting rods, forged aluminum 4.09-inch (104 mm) bore Mickey Thompson pistons, #542990 forged-steel crankshaft with a 4-inch (101.6 mm) stroke and 3+1⁄4-inch (82.6 mm) diameter main journals. Dual Carter Carburetor 500 cu ft/min (14 m³/min) #3433S (front) and #3435S (rear) carburetors with manual chokes and mechanical linkage. Factory heavy-duty high-pressure oil pump and eight-quart sump, four-bolt main bearing caps with Moraine aluminum bearings, and #1110976 dual-point distributor without vacuum advance. Two different cylinder-head castings were used for the 1962 model year, both with a combustion chamber volume of 68 cc (4.15 cu in) to produce an 11.0:1 compression ratio. Casting No. 540306 featured 1.92 / 1.66-inch (49 / 42 mm) valves and was carried over from the previous model year, production stopped in March 1962 and then casting No. 544127 with larger 2.02 / 1.76-inch (51 / 45 mm) valves entered production. Neither casting was equipped with an exhaust crossover.

SD455[]

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Available only in the 1973 and 1974 Formula Firebird and Firebird Trans AM, the SD-455 consisted of a strengthened cylinder block that included 4-bolt main bearings and additional material in various locations for improved strength. Original plans called for a forged crankshaft, although actual production SD455s received nodular-iron crankshafts with minor enhancements. Forged rods and forged-aluminum pistons were specified, as were unique high-flow cylinder-heads. A camshaft with 301/313 degrees of advertised duration, 0.407-inch (10.3 mm) net valve lift, and 76 degrees of valve overlap was specified for actual production engines in lieu of the significantly more aggressive RAM AIR IV style cam that had originally been planned for the engine (initially rated at 310 hp (231 kW) with that cam), but ultimately proved incapable of meeting the tightening emissions standards of the era. The very modest cam, combined with a low-compression ratio of 8.4 (advertised) and 7.9:1 actual resulted in 290 hp (216 kW) SAE NET. The initial press cars that were given to the various enthusiast magazines (e.g. HOT ROD and CAR AND DRIVER) were fitted with the RAM AIR IV style cam and functional hood scoops - a fact that has been confirmed by several Pontiac sources. Some production test cars ran considerably slower and yielded 1⁄4-mile (402 m) times in the 14.5 second/98 mph (158 km/h) range in showroom tune (uncited sources)- results that are quite consistent for a car with a curb weight of 3,850 pounds (1,746 kg) and the rated 290 hp (216 kW) SAE NET figure that some sources suggest was "under-rated." However, in the June 1974 issue of SUPER STOCK AND DRAG ILLUSTRATED, a new 74 Trans Am with the SD-455 motor ran 14.25 @ 101 mph (163 km/h). This was a completely stock car on loan from a private owner for the test. Furthermore, this car had an automatic, air conditioning, a 3.08 axle and weighed 4,010 pounds (1,819 kg). This test would tend to lend credence to the CAR AND DRIVER and HOT ROD tests of 73 SD cars with 3.42 gears, no air, and 160 lb (73 kg) less weight as being representative of production specimens capable of mid to high 13 second passes at 104 mph (167 km/h). Pontiac listed the 290 hp (216 kW) rating at 4000 rpm for a motor that had a 5700 rpm redline on the factory tachometer. Various Pontiac sources have emphatically stated that NO 310 hp (231 kW) versions of the SD455 were installed in regular production cars. The SD-455 motor was listed as an option in dealer brochures for the 73 Grand Am and GTO although none were produced for sale. Nevertheless, there appears in the October 72 issue of MOTOR TREND, a road test of a 73 SD-455 Grand AM. 1975 Factory Service Manual lists the SD455, but the SD455 did not meet emissions for the 1975 model year and was canceled.

Experimental V8s[]

427 Hemi SOHC[]

This was a project started with the end goal of building a 427 Hemi.^[7] Pontiac asked Mopar (Chrysler, Dodge, Plymouth) for help in designing it and making it work. Surprisingly, Mopar actually agreed and sent over several of the engineers that designed both the 392 and 426 Hemi. The goal of making a Pontiac Hemi succeeded but the engine was never produced.

Features:

• Thin-wall, cast aluminum block
• 4.342 in × 3+3⁄4 in (110.3 mm × 95.3 mm) bore x stroke, 8 cylinders, each having a bore of 4.342 inch and a stroke of 3.75 inch, results in a displacement of 444.21 cubic inches (7,279.34 cc); for the Pontiac OHC 427 Hemi refers to it as a "TOHC" and lists the bore at 4.257 inch—which, with a stroke of 3.75 inch, results in a displacement of very slightly more than 426.99 cubic inches (very slightly more than 6997.124 cc).^[8]
• 3 in (76.2 mm) main bearings
• Forged steel 6.625 in (168.3 mm) rods (Ram Air V style)
• 12:1 compression
• Mechanical Port Fuel Injection
• Large-valve heads (valve diameter): 2.4 in (61 mm) intake, 2 in (51 mm) exhaust
• Small-valve high-RPM head (valve diameter) 2.19 in (56 mm) intake, 2 in (51 mm) exhaust
• Splayed main caps, head bolts tie into main caps. Head bolts do not pull on the cylinder wall causing distortion.
• Cam drive: fiberglass belt
• Maximum RPM (high-RPM engine): over 8000 rpm^{[citation needed]}
• Engine weight: estimated 550 lb (249 kg) complete
• Dimensions:
  • width 32 in (810 mm),
  • length 32 in (810 mm)
  • height 24.6 in (620 mm)
• Power: estimated 640 hp (477 kW) at 7500 rpm

421 2 Valve SOHC[]

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3 Valve SOHC[]

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See also[]

• Pontiac Trophy 4 engine
• Pontiac straight-6 engine
• Pontiac straight-8 engine
• List of GM engines

References[]