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Home/Technical Info/Pontiac/01. Engines/ 1961-1977
Large Journal 421-455 V8
/
* 1961-1976 Pontiac Large Journal V8s Described


The first iteration was taken from a Super Duty 389 block.
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Pontiac Large Journal V8s Described

Pontiac V8 engines are broken into two categories, small main journal and large main journal engines. All Pontiac engines have the same deck height except for the 1969 303 Trans Am engine and the short-lived 301 and 265 V8s of the early 80s.

The early 287 -370 engines used smaller main journals, with the first two utilizing 2.5" mains and the 347 and 370 using 2.623" mains. The 301 and 265 reverted to the original 287's 2.5" mains. All 389 and 400 inch engines used "small" main journals which were 3.00". The large main journal engines are listed here.

  • For information on the SMALL journal V8s Part One, click here.
  • For information on the SMALL journal V8s Part Two, click here.

Engines are listed in the order of introduction.

Large Crankshaft Journal (3.25") Engines

421 cu. in. V8 (1961-1966)

Introduced in 1961 as a dealer installed Super Duty option (to bona fide racers), the 421 cu. in. V8 was the 389 design bored to 4.09375" and stroked to 4.00" for 421.2 cu. in. Its primary difference was larger, 3.25" main journals and 4-bolt 2-4 main journal caps. Unlike previous displacement increases of Pontiac V8 engine, it did not replace the 389. The Super Duty versions 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, which was replaced by an "Armasteel" cast nodular iron crankshaft. This became 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 1967, with advent of the 428, Pontiac went to the common "Nodular Cast Iron" name for this crankshaft, which they used until 1975.

The blocks were cast with the provision for 4-bolt mains at positions 2-4 and all large journal engines have this provision, though many "HO" versions are not fitted with 4-bolt caps.

1961

In 1961 the 421 was only offered with dual four barrel carburetors, and was rated @ 373 HP with the two-4-barrel combination.

1962

The 421 Super Duty V8 became factory installed in 1962. It was still primarily a professional racer's unit with a 2 4-barrel Super Duty engine rated at 405 HP (racer's engine) and a "standard" 421, still equipped with 2 4-barrels, rated at a paltry 320 HP.

1963

In 1963 a street version became available from the factory with a four barrel or Tri-power carburetion. These engines were called "HO" for High Output" and did not receive the 4-bolt main caps of the Super Duty. It was offered as a 4-barrel or 3 2-barrel engine. The pedestrian 4-barrel was rated at 320 HP and was installed in the big cars as a step up from the 389, the HO 4-barrel was rated at 353 HP and the 3 2-barrel HO version was rated at 370 HP.

The Super Duty engine came in three flavors: 4-barrel rated at 390 HP and the 2 4-barrel engine which was either 405 or 410 HP depending on the camshaft. All 389 SD engines were dropped.

1964

By 1964, the SD Pontiacs were no more. 421s could be retrofitted with the 4-bolt main caps and the 1962-63 intakes and go racing, but only in NASCAR. By this time lighter cars were prevailing in the stock ranks and the AFX rank cars were all manufactured by privateers and dealerships, so there was no need to deliver these loss-leader cars. Now the 421 came in only three versions, once again the 4-barrel 320 HP big car mover, and a 350 HP 3 2-barrel performance version. The SD engines were gone, now replaced by the HO version with 3 2-barrels and a tougher cam for 370 HP.

1965-1966

For these two years the big car mover 4-barrel got last year's 350 HP cam and moved up to 338 HP. In 1966 a 350 HP 4-barrel engine was added between the 338 and the HO engines. The auto trans HO 3 2-barrel got tweaked timing and moved up to 356 HP, and the big brother stick car was up to 376 HP.

428 cu. in. V8 (1967-1969)

In 1967 the 421 was bored to 4.125" with the same stroke as the 421 at 4.00", increasing its displacement to 427.6 cu in. The crankshaft in the 428 was identified as Nodular Iron by a "N" cast on it as opposed to the 421's Armasteel designation. The 428 was produced from 1967 to 1969.

1967

This engine produced 360 HP in 4-barrel form and 376 HP in HO form.

1968

Starting in 1968, the 3 2-barrel option was dropped and only 2 different 4-barrel engines remained, however the HP ratings were raised to 375 and 390. The 390 was the HO engine.

1969

In 1969, Pontiac issued a revised crankshaft made from Pearlite malleable iron, although it still used the" N" casting designation. This new material had better alloys in the iron. There were two new non-HO engines on at 360 HP and another at 370. Only one HO engine remained, the 390 HP.

455 cu. in. V8 (1970-1976)

For 1970, the 428 bore was expanded to 4.155", combined with a 4.21875" stroke, yielding a total displacement of 457.6 cu in. and bringing it in line with the Oldsmobile and Buick V8s of 455 cu. in. The engine was available on all full-size Pontiacs, the Grand Prix and as the 455 HO in the Pontiac GTO, as GM had lifted its restrictions on the use of engines larger than 400 cubic inches in mid-sized cars.

The 455 was used through 1976. The 455, was "under square" - with a longer stroke relative to bore, emphasized torque over hp, and though advertised as less powerful than some high-performance iterations of the 400, it had a torque rating of 500 ft lbs, which was 55 more ft lbs. of torque than the 1970 performance 400's offered in the GTO and Firebird.

1970

The 1970 455 came in only two flavors, and was used across the board. Though powerful, Pontiac had placed its performance marbles in the hands of the old 400, where the Ram Air III and IV were the true hot motors. Thus while there was a 360 and 370 HP versions, they were not as hefty as their 400 inch counterparts.

1971

The tables were turned in 1971 when the lowered compression killed off the RAM Air 400 cars and all 400s were 3-barrel engines. The 455 came in 280, 325 and 335 HO versions.

The 335 HP HO was a true performance engine, even including the 4-bolt mains and a reinforced block, and improved cylinder head design with 0.125" inch taller intake ports and special round exhaust ports for better breathing, making some 335 hp (310 SAE Net). This was an extremely rare engine that was standard in the Firebird Trans Am.

1972

This year was a real retrenchment for Pontiac, with two 455s offered. The base 455 was replaced with a 4-barrel 400, leaving only the 250 HP and 300 HP versions of the 455.

1973-74

In 1973, a further refined and even stronger version, called the Super Duty (SD) engine was introduced with "only" 310 HP SAE net, using a similar camshaft specifications to the old 1970 Ram Air IV 400. This 455 SD used round port cylinder heads similar to those used on the 1971 455 HO, with specific "LS2" intake and cast iron exhaust header-manifolds. It was considered the most powerful factory installed V8 engine offered that year. In addition to the more refined cylinder heads, there were block casting reinforcements in the lifter galley and in the main bearing oil pan rail area along with the addition of forged connecting rods with larger 7/16" diameter bolts.

Further, the SD was cast with a provision for dry sump oiling from the factory. This truly was a racing engine, detuned for use in passenger cars. It was offered in the Firebird from mid-1973 and 1974, after which point it was discontinued.

Another pedestrian 455 was also available in all other Pontiacs, rated at 250 HP.

1975-1976

In the last two years of its life, the 455 was a mere shadow of its former self, used mostly in big Pontiacs, though available across the line, Choked by a single exhaust and a catalytic converter, made a paltry 200 SAE Net HP. Pontiac's large journal engine went out with a whimper, as did most Detroit big V8s.


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The 1962 421 engine was also cut from the same casting as the 389 Super Duty. Later in the year, a 421-specific block was cast.

The 421 at home in the Big Bad Catalina

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

   


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