Pontiac V8 engine
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From 1955 to 1981 the Pontiac Division of General Motors manufactured its own, unique V8 engines. Displacement began at 287 in³ and grew as large as 455 in³ (7.5 L) by 1970.
An engine of intermediate size (neither a true small-block nor big-block), the Pontiac V8 was a unique design, distinct from Buick, Chevrolet, or Oldsmobile engines.
Pontiac's engines were used in its U.S.-market cars; Canadian Pontiacs generally used Chevrolet engines. From 1955 through 1959 Pontiac's V8 was also used in GMC pick-up trucks.
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[edit] 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 unique feature 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.
The drive towards "corporate" engines shared among all GM divisions led to the progressive demise of the Pontiac V8 in the late 1970s. The last Pontiac V8, a 301, was produced in 1980 for a 1981 automobile.
[edit] Design
The Pontiac V8 was an overhead valve engine with wedge combustion chambers. It used cast iron cylinder heads and a cast-iron block. An unusual design feature was mounting the rocker arms on ball pivots on studs set into the cylinder, rather than using a separate rocker shaft; this allowed more consistent valve action with less weight than a conventional shaft. All (except the 303 Ram Air V engine) 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 plauged with corrosion issues and was removed from the design for the 1960 model year due to warranty returns.
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 (718 mm × 686 mm × 787 mm). Dry weight ranged from 590 lb to 650 lb (270 to 295 kg), depending on displacement and year. Most Pontiac engines were painted light blue. The 389 version was known as the "Tempest" or "Trophy" V8, depending on year and hp rating. Pontiac was one of a few US manufacturers which did not regularly identify its engine names and sizes with air cleaner or valve cover decals.
[edit] Development
[edit] 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. The 287 was an "oversquare" engine with a bore of 3.75 in (95.25 mm) and a stroke of 3.25 in (82.55 mm), for a total displacement of 287 in³ (4.7 L). 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). It was rated 180 hp (134 kW) @ 4600 rpm and 264 ft·lbf (358 N·m) @ 2400 rpm with a two-barrel carburetor, 200 hp (149 kW) @ 4600 rpm and 278 ft·lbf (377 N·m) @ 2800 rpm with the four-barrel carburetor.
[edit] 316
For 1956 the V8 was bored out to 3.9375 in (100.0 mm), increasing displacement to 316 in³ (5.2 L). It was offered in the following forms:
(with manual transmission)
- two-barrel carburetor, 7.9:1 compression, 192 hp (143 kW) @ 4400 rpm, 297 ft·lbf (403 N·m) @ 2800 rpm
- four-barrel carburetor, 8.9:1 compression, 216 hp (161 kW) @ 4800 rpm, 315 ft·lbf (427 N·m) @ 2800 rpm
(with Hydramatic)
- two-barrel carburetor, 8.9:1 compression, 205 hp (153 kW) @ 4600 rpm, 294 ft·lbf (399 N·m) @ 2600 rpm
- four-barrel carburetor, 8.9:1 compression, 227 hp (169 kW) @ 4800 rpm, 312 ft·lbf (423 N·m) @ 3000 rpm
- two four-barrel carburetors, 10.5:1 compression, 285 hp (213 kW) @ 5100 rpm, 330 ft·lbf (447 N·m) @ 2600 rpm.
[edit] 336
The 336 in³ (5.5 L) engine was only used in GMC trucks. The stroke was 3.875 (98.4 mm) and the bore was 3.56 in. (90.4 mm).
[edit] 347
For 1957 the V8's stroke was increased to 3.56 in (90.4 mm), for a displacement of 347 in³ (5.7 L). For the first time, Pontiac offered Tri-Power, three two-barrel carburetors with a sequential linkage (replacing the previous dual-quad set-up). Power ratings increased accordingly:
(with manual transmission)
- two-barrel carburetor, 8.5:1 compression, 227 hp (169 kW) @ 4600 rpm, 333 ft·lbf (451 N·m) @ 2300 rpm
- four-barrel carburetor, 10:1 compression, 244 hp (182 kW) @ 4800 rpm, 350 ft·lbf (475 N·m) @ 2600 rpm
(with Hydramatic)
- two-barrel carburetor, 10.0:1 compression, 244 hp (182 kW) @ 4800 rpm, 350 ft·lbf (475 N·m) @ 2600 rpm
- four-barrel carburetor, 10.0:1 compression, 270 hp (201 kW) @ 4800 rpm, 359 ft·lbf (487 N·m) @ 2900 rpm
- three two-barrel carburetors, 10.00:1 compression, 290 hp (216 kW) @ 5000 rpm, 375 ft·lbf (508 N·m) @ 2800 rpm.
Several dealer-installed camshafts were optional to increase power further to 310 hp (231 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". 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.
[edit] 370
For 1958 the V8's bore was increased again to 4.06 in (103.2 mm), increasing displacement to 370 in³ (6.1 L).
The fuel-injected engine was now an option, not standard, on the Bonneville, carrying a staggering price tag of $500 (almost 15% of the car's base price). It was rated at 310 hp (231 kW) @ 4800 rpm and 400 ft·lbf (542 N·m) @ 3,000 rpm on 10.5:1 compression. Only about 400 were produced before the fuel injection system was quietly dropped.
[edit] 389
For 1959 the V8's stroke was increased to 3.75 in (95.3 mm), raising displacement to 389 in³ (6.4 L). The 389 would remain the standard Pontiac V8 engine through 1966, offered in a bewildering variety of outputs ranging from 215 hp to 360 hp (160 to 269 kW). The 389 was the standard engine for the Pontiac GTO through 1966.
[edit] 326
For 1963 Pontiac dropped the aluminum V8 it had offered on the Pontiac Tempest (which was built by Buick) and replaced it with a small-bore version of the standard 389 Pontiac V8. It shared the 389's 3.75 in (95.3 mm) stroke, but its bore was reduced to 3.72 in (94.5 mm), giving it a displacement of 326 in³ (5.4 L). It is interesting to note that the very first 1963 326 engines used a 3.78 inch bore size for an actual 336 cubic inch displacement. In 1964 Pontiac reduced the bore size to what was correct for 326 inches of displacement, a 3.72 inch bore. It was rated at 250 hp (193 kW) with 8.6:1 compression and 260hp at 10.25:1 compression. Both used a single, two-barrel carburetor. 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 carb, dual exhausts, and higher compression, and was good for 280 hp for 1963-1965, and 285 hp for 1966 and the final year, 1967.
[edit] 400
For 1967, Pontiac introduced the 400 in³ (6.6 L).
The'400'V8 was essentially a bored-out 389 with 4.121 inch bore and 3.75 inch stroke (104.7 mm by 95.3 mm). It replaced the 389 in 1967 and remained in production through the 1979 model year.
The 400 was the only engine installed in '67-69 Pontiac GTOs. It was also the biggest engine available in '67-'69 Firebirds. The 400 was a popular performance option for many of Pontiac's cars. The 400 engine produces a good balance of low end torque and higher RPM horsepower.
In 1967 the cylinder head design was improved for all engines. The valve angle was changed for better breathing. 1967 was the last year for closed chambered heads. The "670" head was a '67-only casting, and the last PMD head to have a closed chamber. Pontiac went to open chambered heads in '67 to improve power, engine breathing and emissions. The valve size increased as well, to 2.11" intake and 1.77" exhaust valves on high performance heads. Low performance and 2bbl applications got 1.96" intake and 1.66" exhaust valves.
[edit] 421
The 421 in³ (6.9 L) was bored to 4.09 in (103.9 mm) and stroked to 4.00 in (101.6 mm), and also featured larger, 3.25 in (83 mm) main journals. Unlike previous enlargements of this engine, it did not replace the 389. Modified 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 crankshaft of the entire Pontiac V-8 line until '67. "Armasteel" was no more than a fancy name for a hardened cast iron unit. In '67, Pontiac went to a Nodular cast iron crankshaft, which they used until 1975.
[edit] 428
In 1967 the 421 was bored to 4.12 in (104.7 mm), increasing its displacement to 428 in³ (7.0 L). The 428 had the same 4.00" stroke as the 421, and was produced from 1967 to 1969. It was replaced by the 455 for the 1970 model year.
[edit] 350
In 1968 the 326 was replaced by the 350, which used a 3.876 in bore and 3.75 in stroke (98.5 by 95.3 mm) for a total displacement of 354 in³ although it was still called a 350 (5.7 L).
[edit] 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 in³ 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. (63.5 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 (72.1 mm) stroke for a displacement of 303 in³ (5.0 L). The short-deck engine weighed about 40 lb (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 in the Pontiac Firebird and 375 hp 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 428 engines were known as the Ram Air VI and Ram Air VII repectively, the difference between them being that the Ram Air VII was developed with twin four barrel carburetors.
[edit] 455
For 1970, the 428 bore was expanded to 4.152 inches, combined with a 4.21 inch stroke (105.5 mm by 106.9 mm), yielding a total displacement of 455 in³ (7.5 L). The engine became available for the first time in Pontiac Firebirds and the Pontiac GTO, as GM lifted its restrictions on the use of big-block engines in mid-sized cars. The Pontiac V8 design differs from other manufacturer's designs in that the external dimensions of each engine, from 326 - 455 in³ displacement, is identical. The displacement is determined internally with changes to the bore and stroke; therefore, there is no "big block" Pontiac engine. The 455 was used through 1976.
The 455, with its "undersquare" dimensions (long stroke relative to bore), emphasized torque over hp, and was somewhat less powerful than some high-performance iterations of the 400. For 1971 Pontiac introduced a High Output, H.O., version with standard internal parts, a 4-bolt main bearing cap equipped block, and improved cylinder head design with 1/8 inch taller intake ports and special round exhaust ports for better breathing, making some 335 hp/224 kW (310 hp in the more accurate SAE net system), but this was an extremely rare engine. In 1973, a further refined and even stronger version, the Super Duty (SD) engine was introduced with "only" 310 hp/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 "LS2" 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 (216 kW) via a camshaft change to the same profile used in the early RAIII 400 engines for mid 1973 and 1974, after which point it was discontinued.
While an evolution of the RAIV 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 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.
[edit] 301
The 301 in³ (4.9 L) 301 was offered from 1977 to 1981. It had a 4.00 in (101.6 mm) bore and 3.00 in (76.2 mm) stroke. Based in part on designs for an abortive "short deck" 303 in³ (5.0 L) engine designed for the 1970 racing season, it had a shorter deck than the big V8, and used thin-wall casting to reduce weight. It produced 135 to 170 hp (97 to 127 kW). The Pontiac 301 EC (Electronic Controls) version offered in 1981 produced 155 hp and 245 ft·lbf of torque, although it's rumored that the actual HP was closer to 170. The 1980 301 Turbo was rated at 210 hp @ 4400 rpm and 345 ft·lbf of torque @ 2800 rpm. The 1981 301 Turbo gained the electronic controls with an O2 sensor, feedback ECM and E4ME Quadrajet providing a slight reduction in power to 205 hp and 240 ft·lbf torque. The 301 has the distinction of being the last true Pontiac motor as Pontiac stopped production of all V8s effective April 1st 1981.
From 1977-1980 there were 4 distinct 301 versions:
301 2BBL (135 hp), 4BBL (150 hp), 4BBL 'HO' or 'EC' (170 hp, which shared the turbo block, the 1979 220 hp 400 camshaft, and had incorporated the Buick design Electronic Spark Controller, ESC, to boost timing) and Turbo (210 hp which also used the ESC).
The 301 Turbo was unique that it had a beefier block than the 77-79 versions, which carried on in the non turbo versions in 1980 and 1981, a very mild camshaft with 0.350" lift and 250 degrees gross duration, a 60 psi oil pump to ensure adequete oil to the oil cooled Garrett TBO-305 Turbocharger, a rolled fillet crankshaft, a fully baffled oil pan, and a specific 800 cfm Quadrajet carburator which had super rich "DX" secondary metering rods and remote vacuum source for the primary metering rod enrichment circuit that allowed the "PEVR", Power Enrichment Vacuum Regulator to release the primary metering rods to move to the up position (enrichment) anytime during boosted conditions to ensure that there was enough fuel to cool the cast offset dish pistons. Boost was wastegate limited to 9 psi. The 301 Turbo package mandated Air Conditioning, automatic THM350 non lockup transmission and 3.08 gears.
The 301 Turbo was limited to Trans Am and Formula Firebird production only. Some literature has indicated that the 301 Turbo may have found its way into the Chevrolet Z28. It is unclear if any were ever produced.
[edit] 265
Based on the same short-deck as the 301, the 265 (4.3 L) was offered only in 1980 and 1981, and featured a smaller bore of 3.75 in (95.3 mm) coupled with the same 3.00 in (76.2 mm) stroke of the 301. It produced 120 hp (90 kW)
The 265 and 301 were the last Pontiac V8 engines to be manufactured. After the 1981 model year, Pontiac adopted the new "corporate" engines.
[edit] Pontiac Four-Cylinder
[edit] 195
Perhaps the most unusual variation of the durable Pontiac V8 was not a V8 at all, but an inline four. 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 4.06 in (103.2 mm) and 3.75 in (95.3 mm) were the same, giving a displacement of 194.4 in³ (3.2 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 lb (245 kg), it was not substantially lighter than the 389.
The 195 produced 110 hp (82 kW) (gross) at 3800 rpm and 190 ft·lbf (258 N·m) at 2000 rpm with a single-barrel carburetor, or 155 hp (116 kW) @ 4800 and 215 ft·lbf (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 in³ (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, but if the engine was out of tune, the shaking grew worse than the mounts could hide. 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 195 was dropped after 1963, although Porsche would use a "half-a-V8" inline-four (with a rear-mounted transmission) for its later Porsche 944 model.
