Chevrolet Straight-6 engine

Chevrolet Straight-6 engine
Straight 6
Manufacturer General Motors Corporation
Production 1929-1990 North America
2002-2009 (Atlas LL8) North America
1962-1999 Brazil
Predecessor 171 Straight-4
Successor GM Atlas engine
Valvetrain OHV
Fuel type gasoline
Cooling system water cooled

The Chevrolet inline 6 was Chevy's main engine from 1929 (when it replaced their first 4 cylinder engine, the 171 cubic inch four), through 1954, and was the base engine starting in 1955 when they added the small block V8 to the lineup. It had finally been completely phased out by 1990 in North America, but Brazil held on to their fuel injected straight-6 through the 1998 model year. It was replaced by more recently developed V6 and four cylinder engines. Many popular cars and trucks, including the Chevrolet Camaro, Chevrolet Impala, and Chevrolet Suburban just to name a few, used the inline 6 as the base engine. Chevrolet did not offer another inline 6 until the 2002 GM Atlas engine's debut in the Chevrolet TrailBlazer.


1st Generation (1929 Stovebolt Era)

First Generation
1929 Chevrolet 2-door sedan engine.JPG
Production 1929-1936
Predecessor 171 Straight-4
Displacement 194 cu in (3.2 L)
181 cu in (3.0 L)
207 cu in (3.4 L)
Cylinder bore 3.3125 in (84 mm)
Piston stroke 3.75 in (95 mm)
Valvetrain OHV
Oil system "splash" lubrication for the rod bearings and pressurized lubrication to the three main bearings.
Cooling system Watercooled
Power output 50 hp (37 kW)1929-1931 194
60 hp (45 kW)1932-1933 194
80 hp (60 kW)1934-1936 194

"A six for the price of a four"

The first mass-produced GM inline 6 was introduced in 1929 on Chevrolet cars and trucks, replacing the company's first inline-4. Richard Grant (Chevrolet marketing executive) insisted that the new design boast overhead valves. Chevrolet had long been known for its "valve-in-head" four-cylinder engines. William S. Knudsen's cast-iron wonder was produced through 1936.


It was 194 cubic inches (3.2 L) in size and produced 50 hp (37 kW). This engine used a forged steel crankshaft with three bearings and cast iron pistons. Bore and stroke was 3.3125 in (84.14 mm) by 3.75 in (95.25 mm). The 194 was shared with Chevrolet and GMC trucks for 1935 and 1936.

A balanced crankshaft was introduced for 1932, while a higher (5.2:1) compression ratio upped output to 60 hp (45 kW). In 1934, a new cylinder head pushed output to 80 hp (60 kW).


  • 1929 Chevrolet Series AC International (Only $10 more than 1928s four cylinder)
  • 1930 Chevrolet Series AD Universal


A 181-cubic-inch (3.0 L) version was used by Chevrolet and GMC trucks in 1935 and 1936.


207-cubic-inch (3.4 L) variant was used by Chevrolet and GMC trucks in 1934, 1935 and 1936.

Why were they called stovebolts?

This name stovebolts came into common use as the 1/4″ × 20 slotted-head bolts are used at numerous points on the engine (and body) of these cars. The slotted-head bolts are commonly used in the assembly of unwelded wood-burning stoves.

Oldsmobile's flathead straight six in Chevy and GMC trucks

In 1935 and 1936, GMC and Chevrolet used an Oldsmobile 213 L-head engine. For 1937 and 1938, they used Oldsmobile's 230 L-head engine.

Second generation

The next-generation Chevrolet inline 6 was introduced in 1937 and phased out in 1963 in the US, and 1979 in Brazil.

Second generation
Production 1937-1963 US
-1979 Brazil
Displacement 216 cu in (3.5 L)
235 cu in (3.9 L)
261 cu in (4.3 L)
Cylinder bore 3.500 in (88.9 mm)
3.5625 in (90.5 mm)
3.750 in (95.3 mm)
Piston stroke 3.750 in (95.3 mm)
3.9375 in (100 mm)
Valvetrain OHV
Compression ratio 6.5:1
Cooling system Watercooled
Power output 85 hp (63 kW)
90 hp (67 kW)
92 hp (69 kW)
123 hp (92 kW)
136 hp (101 kW)
150 hp (112 kW)


This engine had a 216-cubic-inch (3.5 L) displacement with a 3.500” (88.90mm) bore and a 3.750” (95.25 mm) stroke. A four-bearing crankshaft was added, along with 6.5:1 compression pistons, for 85 hp (63 kW). A new cylinder head in 1941 bumped output to 90 hp (67 kW), and 6.6:1 compression gave the 1949 model 92 hp (69 kW). This generation did not use a fully pressurized oiling system. The connecting rods were oiled using an "oil trough" built into the oil pan that had spray nozzles that squirted a stream of oil that the connecting rods (which were equipped with dippers) caught on the fly and supplied the necessary oil for the rod bearings.


In 1941, a 235.5-cubic-inch version of the 216 engine was introduced for use in large trucks. Both the bore (3.5625” or 90.49mm) and stroke (3.9375” or 100.01mm) were increased over the 216. This engine also had a "dipper system" as described above, in reference to the oiling system, as in the 216.

The 235-cubic-inch (3.9 L) version was added to cars in 1950 to complement the new Powerglide automatic transmission, and 3.55:1 rear differential. Hydraulic lifters were used in the Powerglide 235 and a fully pressurized lubrication system was introduced in 1953, but only in cars ordered with the "Powerglide" transmission. The 216-cubic-inch (3.5 L) continued to be standard powerplant for cars with the three speed manual transmission until 1954, when the 235-cubic-inch (3.9 L) became the standard powerplant on all Chevrolet passenger cars. Two versions were used in 1954 cars - a solid-lifter version with 123 hp (92 kW) for standard transmissions and the hydraulic-lifter 136 hp (101 kW) version (the Blueflame) for Powerglide use.

The major limitation for performance on the 235 was the design of the intake and exhaust ports. Unlike more modern straight sixes, the 235 had siamesed ports, with three intake ports and four exhaust ports. This meant the adjacent cylinders 2 and 3 and cylinders 4 and 5 shared a single exhaust port between them, whereas cylinders 1 and 6 had their own exhaust ports. Secondly, since there were only three intake ports, each port was divided between a pair of adjacent cylinders: 1 and 2, 3 and 4 and 5 and 6 shared an intake port. The design of the intake manifold also favored the middle port (and therefore the middle two cylinders). This ultimately caused the four end cylinders to receive less mixture, resulting in an unequal and unbalanced work load between the six cylinders.

From 1954 to 1963, the high-pressure 235 engine with mechanical valve lifters was used in some trucks. From 1956-1962, all 235 engines used in cars had hydraulic lifters.

It is interesting to note the original 1953 Corvette engine was the high-pressure 235 engine equipped with mechanical lifters. A 150 hp 235 engine was used in the 1954 Corvette and into 1955 (until they were all sold). The Corvette 235 was equipped with the same slightly higher-lift camshaft as used in the 261 truck engine and used triple side draft, single barrel, Carter Model YH carburetors mated to a PowerGlide transmission and dual exhaust manifold.

The Chevrolet 235-cubic-inch is known as one of the great Chevrolet engines, noted for its power and durability.

Canadian production GMC trucks used the 216 and 235 Chevrolet straight six engines as their base light duty truck powerplant in the late 1940s and early 1950s in Canada, not USA. The 216 was used from 1947 to 1953, and the 235 was used in 1954 light duty trucks only. Medium duty GMC trucks used US built GMC engines in the 248, 270 and up sizes prior to 1954.

It was optional in Checker Taxis beginning in 1965.[1]

Toyota built the 235 under license as the Toyota F engine from 1955 to 1974.


In 1954, a 261-cubic-inch (4.3 L) truck engine was introduced as an optional Jobmaster engine for heavy-duty trucks. This engine was very similar to the 235 engine, except for a different block casting with a larger piston bore of 3.750” or 95.25mm, two extra coolant holes (in the block and head) between three paired (siamesed) cylinders, and a slightly higher lift camshaft. This engine was offered as a step up from the 235 starting in 1954. It was offered in parallel with the GMC V6 engine in 1960 until 1963, when it was discontinued. The 261 USA truck engine had mechanical lifters and was available from 1954-62. In 1963, the 261 truck engine was available in 4x4 Chevrolet trucks (until the engine sold out).

The 235 and 261 truck engines were also used by GMC Truck of Canada (GMC truck 6-cylinder engines were also used in Canada). The 1955-1962 Canadian full-size Pontiac car had an optional 261-cubic-inch engine that had hydraulic lifters. This engine was not sold in the USA, but was very similar to the USA truck 261.

The 261 engines were also used in light trucks and the Chevrolet Veraneio from 1958 to 1979 in Brazil.

Third generation

Third generation
Production 1962 - 1988
Displacement 194 cu in (3.2 L)
230 cu in (3.8 L)
250 cu in (4.1 L)
292 cu in (4.8 L)
Cylinder bore 3.563 in (90.5 mm)
3.875 in (98.4 mm)
3.875 in (98.4 mm)
3.875 in (98.4 mm)
Piston stroke

3.250 in (82.6 mm)
3.250 in (82.6 mm)

3.530 in (89.7 mm)
4.120 in (104.6 mm)
Valvetrain OHV
Cooling system Watercooled
Length 32.5 in (830 mm)

Chevrolet's third-generation inline six was introduced in 1962 (two years after rival Chrysler introduced its Slant Six), and was produced through 1988. Although the exterior dimensions were similar to the previous stovebolts, this generation was lighter and had a different cast-in bell housing pattern. Manual transmission bellhousings, automatics, and starter motors became interchangeable with both small block and big block Chevrolet V8s.

There were other major differences: The Gen-3 crankshafts had 7 main bearings (increased from 4). The 230 reduced stroke to 3.25" from the comparable 235 design's 3.9375". The combustion chamber changed to a conventional wedge design much like the V8. The harmonic damper gained cast-in pulley provisions. Air-conditioned vehicles had a stamped-steel pulley bolted up front. Stamped and stud-mounted rocker arms were introduced, similar to the V8, and the ratio was close to the one used in the Chevrolet GEN IV big block (1.75:1 ratio) rather than the shaft-mounted earlier rockers at 1.477:1.

The first use was in the newly-introduced 1962 Chevy II; the following year, Chevrolet passenger cars adopted it (alongside Checker Marathons since 1965) and used this powerplant until 1977 (1979 for Camaros, Novas, and full size Chevys). Chevrolet/GMC trucks, which previously used the stovebolts (235 and 261), also used some members of this family from 1963 through 1984, as did Pontiac in 1964 and 1965. A 153 cubic inch inline-4 version of this engine was offered in the Chevy II/Nova line through the 1970 model year. After several years of steadily declining sales (just 3,900 units in the 1972 model year),[2] the straight six was dropped from Chevrolet's full-sized cars for 1973, for the first time since 1928;[2] it would be restored in 1977.[2] (The base six cost about US$334 less than a V8, and weighed some 188 lb (85 kg) less.)[2]

By the mid-1970s, the compact V-design (e.g. Buick 231) led to inline six engines being phased out in passenger cars, but they continued to be installed in trucks and vans until 1988.

Overseas, the third generation of the inline six was mass produced in Brazil. It was used in the Chevrolet Opala from 1969 (230) to 1992 (250). It was already used in light trucks as the A and Chevrolet Veraneio. The Brazilian version of the GMT400 – the Brazilian Chevrolet Silverado – is powered with a 4.1 instead of the Vortec 4300 V6. These inline sixes and their four-cylinder siblings were converted for marine usage by Mercruiser and Volvo Penta, and also used in stationary applications (such as power generation) and in Clark forklifts.


The 194-cubic-inch (3.2 L) 194 was shared between Chevrolet and GMC trucks.



Pontiac's 215 (1964–1965) is documented elsewhere.


The 230 replaced 235 cubic inches (3.9 L). It was also used by Chevrolet and GMC trucks, primarily the half-tons. It produced 140 hp (100 kW). The 230 had a firing order of 1-5-3-6-2-4 rotating clockwise. This engine was used on the following vehicles:

Pontiac 3.8

The Pontiac 3.8 was a special SOHC version of the standard 230-cubic-inch (3.8 L) inline six. An optional W53 version on the Firebird produced 215 hp (160 kW).

This engine was used on the following vehicles:


The stroked 250 version produced 155 hp (116 kW) for Chevrolet and GMC, with a 37/8 in bore and 317/32 in stroke. Between 1975 and 1984, an integrated cylinder head was produced, with one-barrel intakes for passenger cars, and two-barrel intakes for trucks after 1978.

During the mid-1970s, the Buick 231 and Chevrolet V6-90 (basically a variant of the Chevrolet small block V8) was replacing the Chevrolet 250 for use in passenger cars and light duty trucks/vans. Passenger car use of the 250 cu in (4,095 cc) engine was discontinued after the 1979 model year for North America (along with the Chevrolet 292), since the six was restricted to light truck usage (the 4.1 was discontinued after 1984 in North America, where the Vortec 4.3 V6 became the base engine). Brazil held on to the 250 (known as the 4.1 there) until 1998 for passenger cars, when the Chevrolet Omega A was replaced by rebadged Australian Holdens. It was held in Brazil for up to 2001 in Chevrolet Silverado when the line was extinct. It would be GM's final inline six until the introduction of the GM Atlas engine in late 2001.

This engine was used on the following vehicles:


When the long duration races restarted in Brazil, in 1973, the Opala found a great competitor, the Ford Maverick, which was powered by an engine whose displacement was almost one liter bigger. It took Bob Sharp and Jan Balder, that gained a second place in the "24 Hours of Interlagos", in August of that year in an Opala, to pressure GMB to field on race tracks a more powerful engine.

By coincidence, engine development manager, Roberto B. Beccardi, was working on this engine hopping up project out of his own initiative, but he did lack impulse from factory and was not obtaining any approval. This impulse came right from these two pilots.

Thus, in July 1974 GM started to offer the 250-S engine as an option for the Opala 4100. It was slightly different from the version that would be launched two years later: the project of the motor was similar to that of the four cylinders units, did not get a vibration damper and the cooling fan came from the standard 2500, with four blades instead of six.

The Opala was now much faster than the Maverick GT and Ford did not waste time. It quickly homologated a version with four barrel carburetor, called "Quadrijet" in Brazil, and have no relationship with GM own Rochester Quadrajet carburator, found on various GM engines. In the racetracks, the accounting determinative factor for winning was pilots skill and pit organization on the track. The rivals walked side-by-side.

The 250-S has 171 Horsepower and 229.7 lb.-ft. at 2,400 rpm.


The L22 was a 250-cubic-inch (4.1 L) I6 engine produced from 1967 to 1979. The '78 Camaro had 105 horsepower (78 kW) and 190 ft·lbf (260 N·m) of torque with the 250.


The LD4 was a 250-cubic-inch (4.1 L) I6 engine produced strictly in 1978.


The LE3 was a 250-cubic-inch (4.1 L) I6 engine produced from 1979 to 1984.


The 292 was only used in Chevrolet and GMC trucks; the block deck is taller, along with a relocated passenger-side engine mount. These were produced between 1962 to 1990; production of the engine shifted to Mexico after 1980. Year 1988 (only) 115 hp @ 3400 rpm and 215 lb. ft. @ 1600 rpm


The L25 was GM's "last" pushrod straight six engine, produced from 1977 to 1988. It was used in Chevrolet trucks, displaced 292 cubic inches (4.8 L) and produced 115 hp (86 kW) and 215 ft·lbf (292 N·m). This engine was commonly used in UPS trucks through the 1980s, before being replaced by the 4.3L 90 degree V6.

GMC as a marque really only produced a few engine designs, the straight six, a V8, and a V6 which was also available as a V12 for a brief period. GMC used many engines from other GM divisions, as noted below.


GMC replaced the Pontiac 223 with their own 228-cubic-inch (3.7 L) 228 in 1939. This overhead-valve engine was produced through 1953. This is the smallest low-deck engine. Bore was 3-9/16" (3.5625") with 3-13/16" (3.8125") stroke. Connecting rod length was 7.000".


GMC also developed an OHV/pushrod engine in 1939. The 236-cubic-inch (3.9 L) 236 was the first, lasting through 1955. This is a low-deck engine. The bore was 3-5/8" (3.625") with a 3-13/16" (3.8125") stroke. The connecting rod length was 7.000"


Those same years (1939–1955), GMC produced a 248-cubic-inch (4.1 L) engine, the 248, which was similar to the 236. This is the largest low-deck engine. The bore was 3-23/32" (3.71875") with a 3-13/16" (3.8125") stroke. The connecting rod length was 7.000".


The 256-cubic-inch (4.2 L) 256 was different from the 236 and 248. It was also an OHV/pushrod engine, and was built for just two years, 1940 and 1941. This is the smallest raised-deck engine. The bore was 3-11/16" (3.6875") with a 4" stroke. The connecting rod length was 7.54000"


The last GMC-only straight six was the 270-cubic-inch (4.4 L) 270. It was produced from 1941 through 1962, and was an OHV/pushrod engine. This is a raised-deck engine. The bore was 3-25/32" (3.78125") with a 4" stroke. The connecting rod length was 7.000".


The 302 GMC inline six was produced from 1952 to 1960, when it was replaced by the V6. It has a 4.00" bore and 4.00" stroke. The connecting rod length was 7.000". This is the largest raised-deck engine. It was originally designed for the GMC military M135 and M211. It was used in military 2.5 ton trucks with the HydraMatic transmission; however, the engine was a sealed engine for snorkel/submersion use, had an electric fuel pump, and other features such as a deep sump oil pan. From 1952-1959, GMC manufactured the civilian 302 engine, which was not sealed, had a mechanical fuel pump, and used a "standard" oil pan. This engine is popular with hotrod enthusiasts because it delivers tremendous power for an inline six engine, is truck built with a heavy cast block, and can take quite a bit of abuse.


The 426 GMC inline six appeared in 1940s 4x4 Cab Over Engine (COE) trucks made in Pontiac, MI. It also appeared in large GMC trucks in the 1950s.


The 503 GMC inline six was more numerous than the 426 inline six, but beginning and ending dates are unknown. The GMC 630 Series of the early 1950s offered the 503 CID inline six engine.

In 2002, GM announced a new family of straight six engines, the Atlas. Branded by GM under the Vortec name, the Vortec 4200 or Atlas LL8 is currently the only straight six available to the GM family of vehicles.


  1. ^ Flory, J. "Kelly", Jr. American Cars 1960-1972 (Jefferson, NC: McFarland & Coy, 2004), p.341.
  2. ^ a b c d Flory, p.881.

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