Early Chevy Smallblocks: The Truck Connection
THIS TIME WE GIVE YOU THE BASIC XJ SKINNY ON GETTING THE POWER TO THE GROUND. THIS INCLUDES THE TRANSMISSION, TRANSFER CASE AND AXLES.
In 2005, the legendary Chevy smallblock had its 50th birthday. Though the original design has passed on, even the latest high tech Chevy engines share some smallblock DNA, and, there are still millions of original style smallblocks still in loyal service so the legend lives on. It’s also one of the most, if not the most hot-rodded engine of all time with thousands of loyal fans.
The GM mouse motor is most famous in cars, but served ably in trucks as well. The mouse could roar, even when in a work harness. The smallblock found application in the truck lines right from the get-go, but they did not see use in factory built 4x4 trucks until 1960.
The smallblock was introduced for the 1955 model year as a 265ci engine that cranked out 162 gross hp in cars and 155 gross hp in light trucks. What made it special was its compact size and light weight. This came about as GM developed some radical new casting methods. The daddy of the smallblock was a guy named Ed Cole. He took over Chevy’s V8 project in 1952 and immediately scrapped a project to develop a 231ci V8 based on a Cadillac design.
Over the next 15 years, the smallblock grew as large as 400 cubic inches. In total, there were with 10 displacements, seven of which were found in trucks. The 350 rules supreme in trucks, and most would say the same for car applications. Overall, it was the most successful displacement. Of the older engines, the 283 was well-proven and well-loved. The 327 made more of a splash in cars than trucks, but it was still a good truck powerplant. Of the others, none ever descended to the level of boat anchor when judged by the standards of their era.
Covering the multitude of detail changes that came to the smallblock would take volumes, even if we talked just about trucks, but we’ll hit a few of the high spots. Until the early 1960s, GM truck smallblocks followed the typical truck blueprint of the day. This included a lower compression ratio to avoid detonation and high combustion temps under load, a smallish carb to enhance low-end torque, and often, governors. All these features tended to limit power output (but not so much torque) and allowed the engine hold up better in hard use. Later, the engine followed the baseline car engines, which had higher compression ratios, but still only moderate power outputs due to smallish carbs. Until the early-mid ’60s, four-barrel carbs were not common except in large trucks. Throughout the ’60s and ’70s, especially after emission controls became required four barrels became more prevalent as engineers tried to recover some of the lost power.
Smallblock evolution follows a distinct pattern. The Generation 1 (or simply Gen-I) engines were built from 1955 though 1992, almost 40 years! More if you count the replacement engines built in Mexico).The Gen-I engines had many differences between them, but all shared the same basic architecture. The ‘92-up Gen-II engines (commonly known as the Vortec) used heads that were heavily revised, as was the block, though the original smallblock DNA was still very evident. Gen-1 and Gen-II engines coexisted for a time in the ’90s, but the Gen-II changes soon overtook all smallblock applications. In 1997, the Gen-III smallblocks were introduced, and as before, Gen-II and Gen-III coexisted briefly. These new engines arrived with new displacements, 4.8, 5.3 and 6.0L. The Gen-IV engines only recently debuted and are now carrying on the GM smallblock legend. The photos show Gen-I engines used into the early 1980s.
1 The 265ci smallblock of 1955, as illustrated by
the master of the cutaway, David Kimble. The
optional heavy-duty low-compression Trademaster
265s were seen in 4x2 trucks into 1957. The 265
was available in only the 3600 and 3800 series 3/4
and 1-ton trucks for ’55. We’re talking the “real”
trucks, not counting the 1500 series car based
sedan deliveries. In ’56, the low-comp 265 was
added to the 3100 and 3200 series trucks as an
option. The ’55 engines had no provision for an oil
filter on the block, but used an optional remotely
mounted bypass filter. Later 265 engines used a
canister style filter in the now-familiar location.
2 The Trademaster 283 embodied many improvements,
including a 1/8-inch larger bore. It was
used in the lighter duty trucks into the bottom 1-1/2
ton range. It was similar to the base 2-bbl car
engines in most respects. Improvements implemented
to the 283 over the 265 included a full-flow
oil filtration system, engine mounting bosses on
the block and improvements to the lubrication system.
Later ’50s era 283s used a two piece rubber
rear main seal in place of the old rope style.
3 The Taskmaster 283 was a HD engine built for
trucks at or above 1-1/2 ton ratings, but it was
optional in light trucks. The differences in power
were minor between it the Trademaster, but the
Taskmasker featured an even lower compression
ratio, valve rotators, Stellite exhaust valves, hard
seat inserts, special bearings, 4,000 rpm governor,
PCV system and extra oil capacity. The Super
Taskmaster V8, available only in 1-1/2 ton trucks
and up, cranked out 160 hp and featured a four-barrel
carb and dual exhaust.
4 The High Torque series 283s featured a higher compression ratio that upped the power and torque. They
were optional in trucks through the one-tons. The intro of the High Torque series in ’62 generally signaled a
power boost for all the truck engines. That year, GM made cylinder head mods that included port refinements
and larger intake valves (1.94 from 1.72 inches).
5 The first “big” smallblock was the 327, introduced into the truck lines for ’63, though not installed in 4x4s
until ’67. The stroke was increased a full quarter-inch, which required some clearancing in the block, and
the bore was opened up to a full 4-inches. The 327 was a legendary performance engine in cars, but in 2
and 4-barrel forms, it also powered GM trucks into the 3-ton range. It light trucks, the 4-bbl 327 became the
first reasonably high-powered engine you could get in a GM truck. It was still about 30hp less than the L30
car engine, which was at the lower end of the performance engine line. During the last two years of the
327, it featured the big journal crankshaft design that appeared in all Chevy smallblocks after ’67.
6 The High Torque 307 replaced the 283 in ’68. In higher GVW 3/4 and 1-ton trucks, this engine used no
emission controls and made 157hp and 260 lbs-ft of torque. After ’71, emission controls brought this
engine down to 130 hp and 220 lbs-ft. The 307 was basically a 283 block with a 327 crank. It made for a
torquey small-displacement engine. The 307 used the large journal crankshafts. The other ’68 innovation
was a canister style filter replacing the cartridge type.
7 When the High Torque 350 debuted in 1969, it became the top-o-the line powerplant for the GM truck line.
The 350 was a longer stroke evolution of the 327. It had the same bore but a longer 3.48-inch stroke. There
were 2-bbl 350s produced for the commercial trucks, but the light truck engines were 4-bbl. As emission
controls took hold, this engine dropped to as low as 155 hp and 255 lbs-ft. Both two and four-bolt main
bearing truck blocks were produced.
8 The biggest truck smallblock was the High Torque 400. Both the bore and stroke were increased. The
bores were enlarged via Siamesing the cylinders, making the 400 a complex casting. While the 400 was
available in 4x2 trucks as early as ’70, it wasn’t seen in 4x4s until ’75. The first 400s were four-bolt main
engines, but from ’73, only two-bolt blocks were used. While there were 2-bbl 400s produced for cars,
most were 4-bbl in light trucks.
9 The 305 used the long stroke of the 350 but a small bore similar in size to the original 265. In trucks, it
was often seen as the base engine or a mid level engine between the base sixes and the bigger displacement
V8s. The early 305s were 2-bbl engines, but by the early ’80s, a four-barrel was most often seen. The
bigger carb was used to keep power levels up in the face of more stringent emission regulations.