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Pontiac V8 engine

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Pontiac V8 engine

Pontiac began as an adjunct to the Oakland division of the General Motors line of automobiles in 1926. Pontiac successfully competed against more-expensive 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 also had an inline 8 by 1933. These two engines were used through 1954, when Pontiac unveiled its V8 in 1955. From 1955 to 1981 the Pontiac Division of General Motors manufactured its own engines, distinct from Buick, Cadillac, Chevrolet, or Oldsmobile. Displacement began at 287 cu in and grew as large as 455 (7.5 L) by 1970.

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.


The development of Pontiac's OHV V8 dates back to 1946, when engineers began considering new engine designs for postwar cars. Despite these experiments, the division's conservative management saw no immediate need to replace the Pontiac Straight-8 engine, which had served well since 1933. When Robert Critchfield took over as general manager in 1952, however, he launched an ambitious plan to move Pontiac into the upscale, mid-range market segment occupied by Oldsmobile, and that demanded V8 power. The development of the new engine was fast-tracked, but since its relatively late development let it take advantage of the experience gained in the Oldsmobile V8 engine and Cadillac V8 engine, it was remarkably free of teething problems. The main innovation of the Pontiac engine was 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.

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 V8's, a 265 cu in and a 301 cu in, ended production in 1981.

Pontiac also used the Oakland V8 engine in 1932 only. During 1951–1952, Pontiac had 23 1953 model production prototypes running tests on the GM proving grounds. These 23 cars were equipped with the new 287 V8 engine. Pontiac planned to produce the 1953 models with the V8, but Buick and Oldsmobile feared a sizeable loss in customers, if they had to compete with Pontiac having a new V8 engine. After hearing from Buick and Oldsmobile, GM's board of directors ordered Pontiac to delay the V8 introduction until 1955. Pontiac's V8 development that started in 1946 was a 269-cubic-inch L-head design. The 287 cu in overhead design started in 1949. Pontiac engineers tested their 269 V8 in 1949 or 1950 against a downsized Olds rocket V8 overhead engine. The Olds engine was a 303 cu in, Pontiac reduced the size to 270 cu in for testing against the 269 engine. The test results showed Pontiac that a L head engine couldn't compete with the overhead engines.


The 1955-up Pontiac V8 was an overhead valve engine with wedge combustion chambers. It used cast iron cylinder heads and a cast-iron block. 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; this allowed more consistent valve action with less weight than a conventional shaft. It was also cheaper to build than a rocker shaft; this Pontiac-patented technology was immediately handed to the Chevrolet division for their first postwar V-8, which appeared the same year. All (except the 303 Ram Air V engine and 265 and 301) used 6.625 in (168.3 mm) connecting rods.

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.

Most iterations had an overall length (to the edge of the water pump pulley) of 28.25 in, an overall width of 27 in, and a height (not including air cleaner) of 31 in (790 mm) × 686 mm × 787 mm). 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 which did not regularly identify its engine names and sizes with air-cleaner or valve-cover decals.

Engine development: small-journal engines


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 of 3.75 in (95 mm) and a stroke of 3.25 in (83 mm), for a total displacement of 287.2 cu in (4,706 cc). Compression ratio was a modest 8.00:1, with valve diameters of 1.781 in (45.2 mm) (intake) and 1.500 in (38.1 mm) (exhaust). It was rated 180 hp (130 kW) @ 4600 rpm and 264 lb·ft (358 N·m) @ 2400 rpm with a two-barrel carburetor, 200 hp (150 kW) @ 4600 rpm and 278 lb·ft (377 N·m) @ 2800 rpm with the four-barrel carburetor.


For 1956 the V8 was bored out to 3 1516 in (100 mm), increasing displacement to 316.6 cu in (5.188 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 (450 N·m) @ 2600 rpm.


Pontiac V8 engine with Tripower carburetor setup

For 1957 the V8's stroke was increased to 3 916 in (90.5 mm), for a displacement of 347 cu in (5,690 cc). 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 (470 N·m) @ 2600 rpm

(with Hydramatic)

  • two-barrel carburetor, 10.0:1 compression, 244 hp (182 kW) @ 4800 rpm, 350 lb·ft (470 N·m) @ 2600 rpm
  • four-barrel carburetor, 10.0:1 compression, 270 hp (200 kW) @ 4800 rpm, 359 lb·ft (487 N·m) @ 2900 rpm
  • three two-barrel carburetors, 10.00:1 compression, 290 hp (220 kW) @ 5000 rpm, 375 lb·ft (508 N·m) @ 2800 rpm.

Several dealer-installed camshafts were optional to increase power further to 310 hp (230 kW).

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 (220 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.


For 1958 the V8's bore was increased again to 4 116 in (103.2 mm), increasing displacement to 369.4 cu in (6.053 L). The engine is now called the TEMPEST V-8 and will be called this until the end of 1960

The fuel-injected engine was now 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 (230 kW) @ 4800 rpm and 400 lb·ft (540 N·m) @ 3,000 rpm on 10.5:1 compression. Only about 400 were produced before the fuel injection system was quietly dropped.


For 1959 the V8's stroke was increased to 3.75 in (95 mm), raising displacement to 388.9 cu in (6,373 cc). 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 horsepower (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) is now called the TROPHY V-8, due to its many victories in racing.


Pontiac 326 engine in 1967 Firebird

In 1963 Pontiac dropped the Buick division built 215 aluminum V8 it had offered on the Pontiac Tempest and replaced it with a small-bore version of the standard 389 Pontiac V8. It shared the 389's 3.75 in (95 mm) stroke, but its bore was originally 3.997(3.77?) giving it a displacement of 336 C.I.D.It was rated at 250 hp (190 kW) with 8.6:1 compression and 260 hp (194 kW) at 10.25:1 compression. Both used a single two-barrel carburetor. A 4-barrel version was rated at 280 hp. 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. and so the 326 bore size was reduced to 3.72 giving a true 326 The 326 subsequently became the optional V8 engine for Tempests, and later the Pontiac Firebird, through 1967.

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.


For 1967, Pontiac introduced the 400 cu in (6,555 cc).

The '400' V8 was essentially a bored-out (+.060) 389 with 4.1225-inch (104.71 mm) bore and 3.75-inch (95 mm) stroke 400.4 cu in (6,561 cc). It replaced the 389 in 1967 and remained in production through the 1978 model year. The 1979 cars with a 400 had an engine produced in 1978.

The 400 was a popular performance option for many of Pontiac's cars. The 400 produces a good balance of low-end torque and higher-RPM power when used with a four-barrel carburetor or other high-airflow components.

In 1967, the cylinder head design was improved for all engines. The valve angle was reduced from 20 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 last PMD head to have a closed chamber. Pontiac went to open-chambered heads in 1967 to improve power, engine breathing and reduce emissions. The valve size increased as well, to 2.11" intake and 1.77" exhaust valves on high-performance heads. Low-performance and two-barrel applications got 1.96" intake and 1.66" exhaust valves and pressed in rocker arm studs.


In 1968 the 326 was replaced by the 350, which used a 3.88 in bore and 3.75in stroke for a total displacement of 354.74 cu in (5,813.1 cc) or 355 inches although it was still called a 350 (5.7 L). This engine was offered in both 2bbl and 4-barrel variations similar to the previous 326 engine. In 1968 an HO option was available in the Tempest, and Firebirds that were rated at 320 horesepower. This engine was also offered in 1969 along with a second HO version. The later 350 HO was rated at 325 hp, and was equipped with the 400 CI large valve heads (# 48's) and the 400 HO camshaft. In 1974 it was used in the GTO and was rated at 200 hp.


In 1969, Pontiac unveiled its Trans Am model Firebird, and since racing rules required a sub-305 cid engine, Pontiac unveiled the 303 for racing models only, never available to the public. Bore and stroke were 4.121" x 2.840", for 303.63 cu in (4,976 cc). It was rated at 475 hp (354 kW). If you are comparing bore to the 400 pontiac used a 4.121 bore not 4.125 which was the chevy 402.


The 301.6 cu in (4,942 cc) 301 was offered from 1977 to 1981 and also installed in other GM cars during those years. The 301 had a 4.00 in (102 mm) bore and 3.00 in (76 mm) stroke. Based in part on designs for the "short deck" 303 cu in (4,970 cc) 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 HP was closer to 170 hp (127 kW). The 1980 301 Turbo was rated at 210 hp (157 kW) @ 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 than 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), (5th digit of the VIN is a "Y") 301 4-barrel (150 hp), 301 4-barrel 'HO' or 'EC' (170 hp) (with the 5th digit of the VIN being a "W"), and the 301 Turbo (210 hp), 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 .350 in (8.9 mm) lift and 250 degrees gross duration, a 60 psi 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 cfm 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 psi (+/- 1 psi). 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. Some literature has indicated 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.


Based on the same short-deck as the 301, the 265.1 cu in (4,344 cc) was offered only in 1980 and 1981, and featured a smaller bore of 3.75 in (95 mm) coupled with the same 3.00 in (76 mm) stroke of the 301 (same bore and stroke used by Chevrolet when the first small block motor was introduced in 1955). It produced 135 hp (101 kW)

Engine development: large-journal engines


Introduced in 1961 as a dealer-installed Super Duty option that had dual four-barrels, the 389 was bored to 4 332 in (104 mm) and stroked to 4.000 in (101.6 mm) (420.42 cuin), and also featured larger, 3.25 in (83 mm) main journals. Unlike previous enlargements of this engine, it did not replace the 389. The 421 SD became factory installed in 1962 and in 1963 a street version became available from the factory with a four-barrel or tri-power carburetion. The Super Duty versions of this engine were extensively used in


In 1967 the 421 was bored to 4.120. this gave a displacement of 426.61 CID or a 427. The 428 had the same 4.000" stroke as the 421, and was produced from 1967 to 1969. this engine produced 360 hp and 376 hp in 1967, 375 hp and 390 hp in 1968 and 360 hp, 370 hp and 390 hp in 1969. The crankshaft in the 428 also had a "N" cast on them 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 engines were factory install in large cars only. However, there were a few dealers that would install a 428 in a customers GTO or Firebird for higher power levels.

It was replaced by the 455 for the 1970 model year.


For 1970 through 1976, the 428 bore was expanded .030" to 4.150 inches (105.4 mm), combined with a 4.210 inches (106.9 mm) stroke, yielding 455.57 CID. Oldsmobile and Buick also had '455' inch engines about the same time. For the 1970 model year variants of the engine became available on all full-size Pontiacs, the Grand Prix and for the first time as the 455 HO in the Pontiac GTO, as GM lifted its restrictions on the use of engines larger than 400 cubic inches (401 in some Buicks) (455s in some Olds 442s from 1968) in mid-sized cars. The Pontiac V8 design differs from most other manufacturers' designs in that the external dimensions of each engine, from 326 - 455 cu in displacement, is identical (AMCs 290-401 engines identical). The displacement is determined internally with changes to the bore and stroke; therefore, there is no "small-block" Pontiac engine,in fact the same connecting rod length ( 6.625" and journal size remains the same for traditional Pontiac engines of.. ( 287, 316.6, 347, 370, 389, 421, 336, 326, 350, 428, and 455 and the "Indy 4" .) with the exceptions of the later short deck 301 and 265. The 455 was used through 1976.

The 455, with its "undersquare" dimensions (long stroke relative to bore), emphasized torque over horsepower, and though advertised as less powerful than some high-performance iterations of the 400, it had a torque rating of 500 ft/lbs., 55 more ft/lbs. of torque than the 1970 performance 400s. The horsepower ratings of this era were often dubious, with engines rated higher or lower in output for advertising, political, or insurance purposes. Per Pontiac's sales brochure, the 1970 455, for example, had similar parts to the higher-rated Ram Air 366 HP 400 cu. in., including the same 288/302 camshaft (manual transmission 455) yet was only rated at 360 HP. The 1970 Grand Prix with the same specfication 455 was rated at 370 HP. For 1971 Pontiac introduced another High Output, (H.O.), version with standard internal parts, a reinforced block with four-bolt main bearing caps, and improved cylinder head design with 1/8 inch taller intake ports and special round exhaust ports for better breathing, making some 335 hp (250 kW)/224 kW (310 hp in the more accurate SAE Net system), but this was an extremely rare engine (it was standard in the Firebird Trans Am). In 1973, a further refined and even stronger version, the Super Duty (SD) engine was introduced with "only" 310 hp (231 kW)/231 kW (SAE Net) 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, which led engineers to de-tune the engine to 290 hp (220 kW) 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.

While an evolution of the RA IV and H.O. engine 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 along with the addition of forged connecting rods with larger 716-inch-diameter (11 mm) bolts, the SD was made with a provision for dry sump oiling from the factory. This truly was a racing engine, detuned for use in passenger cars.

Ram Air

Ram Air

While not officially called the Ram Air I when it was issued, it was indeed the first in a series of Ram Air V8 engines from Pontiac. This engine was installed in the 1967 GTO/Firebird as the top of the line option and at 360 hp (270 kW) (underrated), it was the most advanced 400 in the line. This carried the "744" 301/313 camshaft, as opposed to the "HO" cam which had less duration and overlap. It also had (along with the HO engine) the famous cast-iron "headers" which were much better at reducing backpressure than the regular manifolds. The cast "997" heads had taller valve spring heights than the standard D-port heads, making these heads unique.

Ram Air II

In 1968, Pontiac manufactured the Ram Air II which was a 400 cubic inch motor. In GTO trim the factory rated the car at 366 HP/445 Tq and 'only' 340Hp/430 Tq in the Firebird despite the fact that the engines were identical (save for a small throttle restrictor tab on the Firebird). The Ram Air II was the first engine that incorporated Pontiac's legendary 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 wild 308-/320-degree duration with 0.470-inch (11.9 mm) lift. This same camshaft was also used in Pontiac's 1969–1970 RA IV production cars. The Ram Air II, when outfitted in the (relatively) lightweight 1968 Firebird, has produced some of the fastest 1/4 mile times of the muscle car era. In recent years, under the pure stock drags racing format, Ram Air II Firebirds (running on bias ply tires) have consistently posted ET's in the low to mid 12-second range. No production Pontiac before or since has run times lower. Without question, the RA II was one of Pontiac's most impressive factory offerings.

Ram Air III

The Ram Air III was the base engine in the Judge series of the GTO in 1969 and 1970. It also was the base engine in the Firebird Trans Am of 1969 and 1970. It basically was a 67-8 H.O version with a "Ram Air" air cleaner assembly. It utilized the 288/302 duration camshaft (auto trans.) and used the "744" cam (301-313) in the earlier manual trans versions, later downgraded to the "068" version. It was rated at 366 bhp in the GTO version. The Ram Air III had used a similar block to the Ram Air IV in that it was drilled for 4-bolt mains but used a cast crank and cast rods, and 2-bolt mains in 1969. In 1970 the casting number #9799914 Ram air III 4-bolt main block, also used the 4-bolt main caps on Ram Air applications. This engine also had the distinction of using the cast-iron "headers" made famous on the original HO engine in 1967.

Ram Air IV

The Ram Air IV replaced the Ram Air II in 1969. 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 .520 thanks to the use of 1.65 ratio rocker arms (vs 1.50). The RA IV, like the RA II that preceded it, used round-port cylinder-heads. The RA IV also used a lightweight aluminum intake-manifold that produced a weight savings of 10-15 lb. 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. Today, any high-compression round-port Pontiac (i.e. RA II or RA IV) is a highly sought after car due to its low production and superior performance on the street and at the strip. After RA IV production ended, Pontiac continued using its round-port cylinder-head design in 1971. However, by this time compression had dramatically dropped off, marking the beginning of the end of the muscle car era.

Ram Air V

(303, 366, 400, 428) In 1969 Pontiac created several versions of their "tunnel-port" engine: a special short-deck version of the V8 for Trans Am racing and a 400 standard deck version. The factory also experimented with 366 and 428 cu in versions. The cylinder-head was patterned after the highly successful Ford 427 tunnel-port head. So large were the intake ports that the pushrods ran through the center of the ports via pressed-in tubes.

303 - The revised engine had shorter connecting rods, smaller 2.5 in (64 mm) journals, special "tunnel-port" heads, and a solid-lifter version of the 400's Ram Air IV camshaft. It shared the 4.125 in (104.8 mm) bore of the 400, but with a 2.84 in (72 mm) stroke for a displacement of 303 cu in (4.97 L). The short-deck engine weighed about 40 pounds (18 kg) less than the 400, and had an 8000 rpm redline. The 303 program was promising, with race-ready engines producing 475-525 hp (354.4-391.7 kW) and slated for advertised ratings of 355 hp (265 kW) in the Pontiac Firebird and 375 hp (280 kW) for the Pontiac GTO. Concerns about emissions, the response of the automobile safety lobby, and the warranty implications of a high-revving street engine led to its cancellation. SCCA Trans-Am series General Competition Rules required an engine to be a "Production" item, and required a production of no less than 250 units. The total number of Ram Air V 303 engines produced is not known, estimates range from the SCCA required 250 units, up to 500 units, with rumors of a handful of Ram Air V 303's making their way into the Pontiac Trans-Am production line. These engines are extremely rare and parts not readily available.

The Super Dutys




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 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 (230 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 SAE NET HP. 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. Actual production test cars ran considerably slower and yielded 1/4 miles times in the 14.5 second/98 MPH range in showroom tune - results that are quite consistent for a car with a curb weight of 3,850 pounds and the rated 290 SAE NET HP figure that some sources suggest was "under-rated." Various Pontiac sources have emphatically stated that NO 310 hp (230 kW) versions of the SD455 were installed in regular production cars. 1975 Factory Service Manual lists the SD455, but the SD455 did not meet emissions for the 1975 model year and was canceled.


While not a V8, the SD4 (Super Duty 4-cylinder) was the last in a line of high-performance Pontiac engines. A 2.7L 232 hp (173 kW) SD4 engine powered the 1984 Indy Fiero Pace Car to over 138 mph (222 km/h) during the race. The SD4 was never available in a production vehicle, however Pontiac's Performance Parts counter had all the SD4 parts available and one could garner a 2.7L 272 hp (203 kW) version and a 3.2L 330 hp (250 kW) version. All 2000 Indy Fiero replicas came with the 2.5L 92 hp (69 kW) Iron Duke engine.

Pontiac HO engines

326 HO

350 HO

In 1968, there was also a 350 "HO" which had an 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 chamber for higher compression, along with larger 2.11" and 1.77" valves. Free-flowing exhaust manifolds from the 400 RamAir were used late in the model year. This was underrated at 325 hp. 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.

This may be today one of the most overlooked high-performance engines of the era, as it was overlooked by the buyers of larger 400 engines available in the day.( It was basically a 350 with 400 heads to match the pistons.)

400 T/A 6.6

In 1977 the 400 cubic inch 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, specific camshaft and 3.23 gearing it made 200 hp (150 kW). The base 400 engines in 1977-78 produced 180hp. In 1978 a new dual muffler exhaust was added making 220 hp (160 kW), 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 and the 301 HO. 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. 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 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, but this is incorrect. (Note: In 1980-81, this would change as the 5.0 (305 CID) 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.

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.

421 HO

First offered as an option in 1963, the 421 HO came in a 4-barrel engine of 320 hp and with a tri power engines of 353 hp and a H-0 version of 370 hp. 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. By 1966 the H-O version would be 376 hp.

455 HO

The 455 HO designation made its debut in 1970;
Rated at 360 (or 370 horsepower depending on which vehicle it was installed into) & 500 ft/lbs 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 simplfy 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.

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 800cfm Rochester Quadra-jet carburetor with specific jetting.
The 1971 455 HO was rated at 335 hp @ 4,800rpm & 480 ft/lbs of torque @ 3,200rpm (gross).
The 1971 455 HO was available in the Firebird (Formula and Trans Am), and the GTO.

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 750cfm 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 @ 4,000rpm & 415 ft/lbs of torque @ 3,200rpm.
The 1972 455 HO was available in the Firebird (Formula and Trans Am), and the GTO.

After the 1974 SD455 was dropped the 1975 Firebird's top performance engine was an 'L78' Pontiac 400cid.
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
  • Borg Warner '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 @ 3,500rpm (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.

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 455cid 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 (130 kW) with only 4.9L (301 CID) for the 1980–1981 model years.

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" ram air duct to the air cleaner, specific carburetor calibration for the 301 HO, and cam similar in grind to the 220 hp 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.

Pontiac experimental V8 engines

427 Hemi TOHC

This was a project started by Pontiac with the end goal of building a Pontiac 427 Hemi. 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 was never produced.

Features: Thin Wall, Cast Aluminum Block 4.257 Bore x 3.75" stroke (3.0" Mains) Forged Steel 6.625" rods (Ram Air V style) 12:1 compression Mechanical Port Fuel Injection

Large Valve Heads: 2.40" Intake Valve 2.00" Exhaust Valve

Small Valve High Rpm 2.19" Intake Valve 2.00" Exhaust Valve

Splayed Main Caps, head bolts tie into main caps. Head bolts do not pull on the cylinder wall causing distortion. Cam Drive: Fiberglass Belt Max RPM (High RPM Engine): >8000 rpm Engine Weight: Estimated 550 lb (249 kg) complete

Dimensions: Width: 32" Length: 32" Height: 24.6"

Power: estimated 640 hp (480 kW) @ 7500 rpm

421 2 Valve SOHC

3 Valve SOHC

389 4 Valve DOHC

Originally made in 1966 for the Pontiac GTO.

Pontiac four-cylinder


195.5 cu in (3.2 L) engine in a 1962 Pontiac LeMans Tempest

Perhaps the most unusual variation of the durable Pontiac V8 was not a V8 at all, but an inline four. Nicknamed the "INDY 4", created for the 1961 Pontiac Tempest, it was essentially the right bank of the 389, sharing most of its tooling and many of its parts (more than 120 were identical). The bore and stroke of 4 116 in (103.2 mm) and 3 34 in (95.2 mm) were the same, giving a displacement of 195.5 cu in (3.204 L). This degree of commonality enabled it to be produced on the same lines as the V8, allowing substantial cost savings. A drawback was that the 195 weighed much more than a purpose-designed engine: at about 540 pounds (240 kg), it was not substantially lighter than the 389.

The 195 produced 110 hp (82 kW) (gross) at 3800 rpm and 190 lb·ft (260 N·m) at 2000 rpm with a single-barrel carburetor, or 155 hp (116 kW) @ 4800 and 215 lb·ft (292 N·m) @ 2800 rpm with the optional four-barrel carburetor. For 1962 a "power pack" option increased rated power to 166 hp (124 kW).

The Achilles heel of the 195 was engine shake. An inline four-cylinder engine produces unbalanced "couple," shaking in the vertical plane, and modern engineers consider the installation of twin counter-rotating balance shafts necessary for engines much larger than 122 cui (2.0 L). The V8-based design of the 195 had no such balance shafts, and costs prohibited adding them. The 195 was instead cushioned by flexible rubber engine mounts designed to isolate the engine from the rest of the car, and its forces were further dampened by the Tempest's unusual driveshaft. However, if the engine was out of tune or if a spark plug became fouled, the shaking overwhelmed the dampening of the mounts. A special high-strength timing chain was developed especially for the Tempest 4, since a standard chain would stretch and break rather easily from the inherent vibration in this engine design. The timing chain in the 195 was the same as the 389 initially; the upgraded Tempest chain also works on the V8 engines as a high strength upgrade. As an aside, former Pontiac engineer Malcolm McKellar joked in an interview with Collectible Automobile magazine that he and his fellow engineers sometimes called the four-cylinder Tempest "a traveling fatigue machine."

The 195 was dropped after the 1963 model year.

See also


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