Pontiac V8 engine

History

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 V8s, 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.

Design

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. This handing over Pontiac's valve train invention ( Engineer Clayton leach ) violated GM's rule for a division having a one model year exclusivity, but alas Ed Cole at Chevrolet got his way. 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.

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 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.

317

For 1956 the V8 was bored out to  3 ¹⁵⁄₁₆ in (99.3 mm), increasing displacement to 316.6 cu in (5.188 L). It was offered in the following forms:

(with manual transmission)

(with Hydramatic)

347

For 1957 the V8's stroke was increased to  3 ⁹⁄₁₆ in (102.9 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)

(with Hydramatic)

Several dealer-installed camshafts were optional to increase power further to 317 hp. 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 (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.

370

For 1958 the V8's bore was increased again to  4 ¹⁄₁₆ in (104.3 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.

389

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.

195 Inline 4-cylinder

Perhaps the most unusual variation of the durable Pontiac V8 was a 195.5 cu in (3.204 L) inline four created from the right bank of the 389 for the debut of the Tempest in 1961. With an identical bore and stroke of  4 ¹⁄₁₆ in (103.2 mm) and  3 ³⁄₄ in (95.2 mm) it was precisely half the displacement of the 389. Nicknamed the "INDY 4", it shared most of the 389's tooling and up to 120 of its parts. 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 inline-4: at about 540 pounds (240 kg), it was exceptionally heavy for any form of four-cylinder.

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 adding a four-barrel carburator increased rated power to 166 hp (124 kW).

The Achilles heel of the 195 was engine shake. An inline four-cylinder engine suffers from secondary imbalance. This is caused because of the 180 degree crankshaft. In this design, the two outside cylinders are always moving together and the two inside cylinders are doing the same. But due to geometry, a piston descending from top dead center will always move quicker through the first 30 degrees of crankshaft travel than a piston moving upward from bottom dead center, meaning that more mass is moving downward than is moving upward, causing a shaking in the vertical plane. 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 since 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 (which connected to a transaxle mounted in the rear). However, if the engine was out of tune or if a spark plug became fouled, the shaking overwhelmed the dampening of the mounts. The timing chain in the 195 was originally the same as the 389, but was prone to stretch and break from engine vibration; a special high-strength version was developed as a replacement. This also works on the V8 engines as a high strength upgrade.

The 195 was dropped after the 1963 model year.

326

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. Pontiac V8. It shared the 389's 3.75 in (95 mm) stroke, but its bore was 3.78 in (96.0 mm) for 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. 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 cu.in. The 326 subsequently became the optional V8 engine for Tempests, and later the Pontiac Firebird, through 1967.

A higher-output four-barrel carburetorversion 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 and replaced it with the 400 cu.in. (6.6 L), a 389 bored-out by +.060 to a 4.120-inch (104.6 mm) bore and 3.75-inch (95 mm) stroke. The 400 remained in production through the 1978 model year, with 1979 cars receiving engines produced the previous year.

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, the standard engine in full-sized Pontiacs, got 1.96" intake and 1.66" 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.

350

In 1968 the 326 was replaced by the similarly 389-derived 350, which used a 3.875 in bore and 3.75 in stroke for a total displacement of 354.74 cu in (5,813.1 cc). Like the 326, it was offered in both 2-barrel and 4-barrel versions. In 1968 a 320 horesepower HO option was offered in the Tempest and Firebird. The 1969 HO 350 HO was equipped with the 400 cu. in.'s large valve heads (# 48's) and the 400 HO camshaft and rated at 330 hp. In 1974 it was used in the GTO and was rated at 200 hp.

303

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 4.126 which was the chevy 402.

301

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 in (100 mm) bore and 3.00 in (76 mm) stroke (bore/stroke combination was also used by Ford and Chevrolet (as the standard motor with the first generation Camaro Z28). 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. One owned by McCoy Scott of Houston, TX

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, 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.

265

Based on the same short-deck as the 301, the "LS 5" 265.1 cu in (4,344 cc) was offered only in 1980, 1981, and 1982, 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 120 hp (89 kW) After 1982, the Pontiac V8 was replaced entirely by the GM "corporate" V8's from Chevrolet and Oldsmobile.

421

Introduced in 1961 as a dealer-installed Super Duty option with dual four-barrel carburators, the 421 was a 389 bored to 4 ³⁄₃₂ inches (103.98 mm) and stroked to 4 in (101.6 mm) for a displacement of 421.19 cu.in. It also featured larger 3.25 in (82.55 mm) main journals. Unlike previous enlargements of Pontiac V8s, 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 NASCAR stock car racing and drag racing competition.

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, 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 bored to 4.12. this gave a displacement of 426.61 CID or a 427. The 428 had the same 4" stroke as the 421, yet retained the 421's 3.25" Main journal, 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 installed 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.

455

For 1970 through 1976, the 428 bore was expanded .030" to 4.15 inches (105 mm), combined with a 4.21 inches (107 mm) stroke, yielding 455.34 CID.The 455 Still used the Larger 3.25" Main journal common to this family of engines. 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.

Though advertised as less powerful than some high-performance iterations of the 400, the 455 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 specification 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 ⁷⁄₁₆-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

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 "670" 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. However, the RA II was limited to a 1.52:1 rocker ratio, while the RA IV used a 1.65:1 ratio, which yielded significantly greater total lift and, therefore, superior flow and power. 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. Some 40 years after production and under the pure stock drag racing format, a Ram Air II Firebird (running on bias ply tires) posted ET's in the low to mid 12-second range*.

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 main bearing caps but used a cast crank and cast rods, and 2-bolt main bearing caps 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

In 1969 Pontiac created four versions of the Ram Air V engine: a 303 cu in (4.97 L) short deck version for SCCA Trans-Am racing, a 366 cu in (6.00 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 (7.01 L) adaptation for drag racing. 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. 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 4.171 in (105.9 mm) bore of the 400, but with a 2.84 in (72 mm) stroke for a displacement of 303 cu in. 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. The total number of Ram Air V engines produced is not known and a handful of Ram Air V 303's may have made their way onto the Pontiac Firebird Trans Am assembly line. Only about 25 303 cu in engines were produced and about a dozen 428s and 366s. More 400 cu in engines were produced by Pontiac than the other versions - estimates range from 80 to 200 units. Quite a few 400s were dealer installed. Ram Air V engines are extremely rare and parts are not readily available.

SD455

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.

SD4

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.

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 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 330 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 180 hp. 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 Olds 403 were 6.6 litre decals. (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 two Tri-Power versions of 350 hp and a H-O version with a hotter cam and efficient iron exhaust manifolds and rated at 370 h.p. 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 1965 and 1966 the same combinations would be rated at 338 h.p. for the 4bbl and the two Tri-Power versions would be rated at 356 h.p. and the H-O version at 376 h.p.

455 HO

1970
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.

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 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.

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 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.

1975
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:

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.

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 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.

427 Hemi SOHC

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 4.342 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

389 4 Valve DOHC

Originally made in 1966 for the Pontiac GTO.