Pontiac V8 engine

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 3.9375 in (100.01 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.

347

Pontiac V8 engine with Tripower carburetor setup

For 1957 the V8's stroke was increased to 3.5625 in (90.49 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, 10.25:1 compression, 270 hp (200 kW) @ 4800 rpm, 359 lb⋅ft (487 N⋅m) @ 2900 rpm
• Three two-barrel carburetors, 10.75:1 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 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 (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 (103.2 mm), increasing displacement to 369.4 cu in (6.053 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 (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 (95.3 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.

326

Pontiac 326 engine in 1967 Firebird

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 333.99 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 (5.4 l). and so the 326 bore size was reduced to 3.72, giving a true 326 cu in (5.34 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 (6.6 L), a 389 bored-out by +0.060 in (1.5 mm) to a 4.12 in (104.6 mm) bore and 3.75 in (95.3 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 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.

350

In 1968 the 326 was replaced by the similarly 389-derived 350, which used a 3.875 in (98.4 mm) bore and 3.75 in (95 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 bhp 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 (250 kW). In 1974 it was used in the GTO and was rated at 200 hp (150 kW) (net).

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 in × 2.840 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 (4,942 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. 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 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, 110 kW), 301 4-barrel 'HO' or 'EC' (170 hp, 130 kW) (with the 5th digit of the VIN being a "W"), and the 301 Turbo (210 hp, 160 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 .350 in (8.9 mm) lift and 250 degrees gross duration, a 60 psi (410 kPa) 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 (62 ± 7 kPa). 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 350, the "LS 5" 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 120 hp (89 kW) After 1981, 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 carburetors, the 421 had a bore of 4 ³⁄₃₂ inches (103.98 mm) and stroke of 4 in (101.6 mm) , for a displacement of 421.19 cu in (6,902.1 cc). It also featured larger 3.25 in (82.55 mm) main journals (which the legendary Smokey Yunick reputedly left Pontiac's engineering department over). 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 dual 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 premier SD421 cylinder head was the late 1962-early 1963 casting #9771980 aka "980" head, 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, 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 basic 421 design's bore was increased to 4.12 in (105 mm). this gave a displacement of 426.61 cubic inches (6,990.9 cc) or a 427. The 428 had the same 4 in (100 mm) stroke as the 421, yet retained the 421's 3.25 in (83 mm) Main journal, and was produced from 1967 to 1969. This engine 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 (270, 280 and 290 kW) 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. All 428 cylinder heads received the 14 degree valve angle, closed chamber only in 67 and open chamber 68 and up.

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

455

For 1970 through 1976, the 428 bore was expanded .030 in (0.76 mm) to 4.1525 in (105.47 mm), combined with a 4.21-inch (107 mm) stroke, yielding 456.12 cu in (7,474.5 cc)^[2].The 455 Still used the Larger 3.25 in (83 mm) 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 (6,600 cc) (401 (6,570) in some Buicks) (455 (7,460) in some Olds 442s from 1968) in mid-sized cars. Pontiac differed from most other manufacturers in that the external dimensions of all their V8s, from 326–455 cu in (5,340–7,460 cc) were the same. The displacement is a function of the engines bore and stroke. Pontiac did not have the customary "small-block" and "big-block" engine families common to other GM divisions as well as Ford and Chrysler. Pontiac's V8s share the same connecting rod length 6.625 in (168.3 mm) (and connecting rod journal size) with the exceptions of the later short deck 301 and 265.

Though advertised as less powerful than some high-performance iterations of the 400, the 455 had a torque rating of 500 lb⋅ft (680 N⋅m), 55 more lb⋅ft (75 N⋅m) 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 306 hp (228 kW). The 1970 Grand Prix with the same specification 455 was rated at 370 hp (280 kW). 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 (3.2 mm) 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 year after Detroit went to more realistic SAE net horsepower ratings, a further refined and even stronger 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, 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.

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

Ram Air II

In 1968, Pontiac manufactured the Ram Air II which was a 400-cubic-inch (6,600 cc) motor. In GTO trim the factory rated the car at 366 HP/445 Tq (273 kW/617 N⋅m) and 'only' 340Hp/430 Tq (250 kW/580 N⋅m) 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 1.50:1 rocker ratio, while the RA IV used a 1.65:1 ratio, which yielded significantly greater total lift and, therefore, superior flow and power.

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 (273 kW) 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 in (13.2 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 spherized-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 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.^[3] 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 mm) stroke for a displacement of 303 cu in (4.97 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 . 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 (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.^[3] Ram Air V engines are extremely rare and parts are not readily available. Ram Air V cylinder heads as used on the 400 CID version had an intake port volume of 290 cc (18 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) @ .800 in (20.3 mm) valve lift; in the realm of the NASCAR-dominating Chrysler 426 Hemi. With the intake port pushrod tube airfoils removed, intake port volume was further increased to 315 cc (19.2 cu in).

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 4.00-inch (102 mm) stroke and 3.25-inch (83 mm) diameter main journals. Dual Carter 500cfm #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 (4.1 cu in) to produce an 11.0:1 compression ratio. Casting No. 540306 featured 1.92/1.66-inch 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

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 (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 (220 kW). 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 (0.40 km) 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 (1,750 kg) and the rated 290 SAE NET HP 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 (1,820 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). It should be noted that Pontiac listed the 290 hp 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 (230 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.

SD4

While not a V8, the SD4 (Super Duty 4-cylinder) was the last in a line of high-performance Pontiac engines. A 2.7 l (165 cu in) 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 2.7 l (165 cu in) 272 hp (203 kW) version and a 3.2 l (195 cu in) 330 hp (246 kW) version. All 2000 Indy Fiero replicas came with the 2.5 l (153 cu in) 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 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 (4.1 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.

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 (6,600 cc) 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), 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. 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 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 (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 (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).

455 HO

1970

The 455 HO designation made its debut in 1970; Rated at 360 or 370 horsepower (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 simpilfy 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) @ 4,800rpm & 480 lb⋅ft (650 N⋅m) 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 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) @ 4,000rpm & 415 lb⋅ft (563 N⋅m) @ 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 400 cu in (6,555 cc).

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 (149 kW) @ 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 455 cu in (7,456 cc) 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 4.9 l (299 cu in) 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 in (100 mm) 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 with the end goal of building a 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 in (110.3 mm) bore
  • 3.75 in (95 mm) stroke
• 3 in (76 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, 2.00 in (51 mm) exhaust
• Small-valve high-RPM head (valve diameter) 2.19 in (56 mm) intake, 2.00 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
• 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 (480 kW) at 7500 rpm