Chevy Small Block History - The Best Things Come In Small Packages
More Than 50 Years of Small-Block Chevys
From the May, 2006 issue of Chevy High Performance
By Bob Mehlhoff
Photography by Bob Mehlhoff, GM Powetrain, Jeff Smith
It all started in '55 with...
It all started in '55 with just 265 ci and 162 hp with a two-barrel carburetor. Four-barrel versions in passenger cars pumped out a neck-snapping 180 horses with dual exhaust, and the Corvette version of the 265 small-block garnered 195 horses.
For '57 Chevrolet increased...
For '57 Chevrolet increased the small-block Chevy's bore from 3.75 to 3.875, which increased the displacement to 283ci. This example in a '58 Corvette produced 230 hp.
Dual-quads and a high-lift...
Dual-quads and a high-lift cam in '57 equaled 270 hp from 283 ci. This carburetor and intake system was paired with cylinder heads featuring 1.72/ 1.50 valves and 56cc combustion chambers.
The famed camel-hump (or fuelie)...
The famed camel-hump (or fuelie) heads used until '68 had no accessory bolt-holes and used 1.94 or 2.02 intake valves, depending on application. Most camel-hump heads had the 1.94 intake valves.
This 340hp 327 is being prepped...
This 340hp 327 is being prepped for reinstallation in this '63 split-window Vette. The engine for this application uses a carburetor.
Mechanical Rochester fuel-injection...
Mechanical Rochester fuel-injection systems like this one helped improve the torque curve, allowed easier starting (when operating properly), and improved fuel distribution. Because of its uniqueness, service repairs were difficult. The engine shown here has been installed into an early Nova with lots of polishing and chrome
This '67 325hp (offered in...
This '67 325hp (offered in the Chevelle and Nova) 327 (L79) featured an aluminum intake manifold, larger valves, a high-lift hydraulic camshaft, and dual exhaust. This package is very rare. Most other four-barrel 327 engines in '67 were of the 275hp variety.
All '67-69 Z/28 Camaros used...
All '67-69 Z/28 Camaros used the 302 engines. Very underrated at just 290hp, these little engines would easily rev past 7,000 rpm.
In '70 the LT1 350 engine...
In '70 the LT1 350 engine was rated at 360hp in the Z28 and 370hp in the Corvette. Compared to the Z28 engine one year earlier, the LT1 350 provided lots of low-speed torque the 302 did not offer, but lacked the unique driving personality the 302 displayed. The first LT1 small-block was the only engine available standard in the Z28 from '70 through '72 and optional in the Corvette for the same model years. This small-block featured a mechanical camshaft, a Holley carburetor, and big 2.02 heads. For '70 these engines had 11:1 compression, and 9:5:1 for '71 and '72.
During the mid-'80s Chevrolet...
During the mid-'80s Chevrolet released the tuned-port fuel-injected 5.7L small-block. Also new was the serpentine belt system. This engine is an '85 L98 fuel-injected tuned-port.
In '92 Chevrolet released...
In '92 Chevrolet released the Gen II 5.7L (350) LT1 engine (not to be confused with the earlier LT1). This engine featured reverse-flow cooling, revised cylinder head design, a crank-triggered optical distributor, and electronic fuel injection.
Today's hot-rodded small-block...
Today's hot-rodded small-block Chevys are typically based on lots of cubic inches, bigger and better-flowing aftermarket cylinder heads, and highly developed camshafts. Engines like this 383 make huge amounts of torque for impressive performance on the street and the track.
It's new, powerful, and packed with the latest technology. In 1955 those words described the first small-block Chevy, the 265, with its passenger car rating of 162hp. Soon after the first 265s hit the showrooms, customers sought even more performance and Chevrolet responded with the 283 in '57 and then the 327 in '62. By the late '60s, high-winding 302 engines and powerful 350s continued the trend. By '70, Chevrolet released the big-inch 400 small-block. Later, custom bore and stroke 365 small-blocks, 377, 383, and 406 displacements appeared on the hot-rodding scene.
Today, Vortec and LS-series engines are excellent performers and provide very acceptable fuel economy. The most powerful factory small-block Chevy so far (the '06 427ci LS7 engine) boasts titanium rods, a dry-sump oiling system, an all-aluminum block and heads, and 505 horses. This LS7 small-block will shove an '06 Z06 Vette from 0 to 60 mph in 3.5 seconds, cover the quarter-mile in 11.50 seconds, and continue on to 195 mph; and it's EPA rated at 26 mpg on the highway. Who said good gas mileage cars are boring?
What this all means is that the small-block Chevy has both a tremendous history and a spectacular future. GM has estimated that through 2005, more than 90 million small-block Chevys have been produced. Here we'll chronicle the benchmarks, how hot-rodding has improved power over the years, and where GM development is currently headed. Better cylinder heads, carburetion, fuel injection, improved bore and stroke relationships, and more have all been directed at the engine that is arguably the most hot-rodded in the world. As always, the small-block Chevy is powerful and packed with technology.
Efficient Design With the Gen I
In the early '50s, Chevrolet engineers specifically designed the small-block engine in a compact size to allow a streamlined production process. New innovations, such as greensand casting, meant the block could be cast upside down, thus reducing the amount of cores. The small size of the block provided an economical use of iron and required less cooling effort in service. To provide high-rpm operation, engineers designed lightweight rocker arms from stamped steel. The 265 engines used a 3.00-inch stroke and a 3.75-inch bore. The new small-block's cylinder heads with a cross-flow port structure and wedge combustion chambers allowed for a broad powerband. The new small-block engine was designed with 4.4-inch bore centers (measured as the center of one cylinder to the next) and is the same dimension carried through to the Gen III small-block designed in '97. Other new designs for the small-block Chevrolet included:
* Hollow pushrods to carry oil to the cylinder heads
* A one-piece intake manifold combining the water outlet, exhaust heat riser, distributor mounting, and lifter valley cover in a single component
* An internal oiling system
1 HP/CI Early On
Although at the upper end of engine options, dual quads had been offered on the 265 with a high-lift cam and 240 hp, the era demanded not only more power, but also broadband performance. So the new-for-'57 283 with its 0.125-inch larger bore (3.875-inch bore, 3.00-inch stroke) was available with the standard two-barrel, four-barrel, dual quads, or a new mechanical fuel-injection system that produced 283 hp from 283 ci (1 hp per cubic inch). All cylinder heads for the 265s and 283s used 1.72/ 1.50-inch valves.
For '62 Chevrolet's new hot motor, the 327 (the first small-block with a four-inch bore) packed a wallop. Besides the carbureted versions, a fuel-injected 327 with 360 hp was optional in the '62 Corvette. The cylinder heads used on this engine (and some others of the era) were the 3782461X head with 1.94/1.50-inch valves. These heads had the commonly found double-hump shape on the end of the head. It should be noted that beginning in '64 and through '68, cylinder heads with the double-hump shape also used 2.02-inch intake valves (aka fuelie heads). Castings with 2.02-inch intake valves were also used on the 365hp (Holley carburetion) and 375hp (Rochester fuel-injection) Corvette 327 engines. Except for some early truck applications, it would not be until '69 that all small-block cylinder heads would feature accessory mounting holes.The '67 model year had a lot of small-block excitement. First, the new 350 engines available in the Camaro debuted, and the special high-performance 302 Z/28 package Camaro was released. The 350ci engine with its 3.48-inch stroke and 4.00-inch bore provided good low-speed torque and power. The Camaro-only 350 engine (for '67) produced 295 hp from a two-bolt main block. Other passenger cars would have 350s beginning in '69.
The 302 Z28 engine is the smallest V-8 ever installed in a Camaro to date. It is also the only engine available new in any '67-69 Z28. Based on a 4.00-inch bore and a 3.00-inch stroke, the little engine made lots of power above 5,000 rpm and very little below. This engine's 290hp rating was very underrated. In stock trim, actual power was in the mid-300hp range. These engines were designed specifically to compete in SCCA road racing and came with a huge resume of hardcore race parts: a Holley 800-cfm carburetor, big-runner aluminum intake manifold, 2.02 heads, a high-lift mechanical camshaft (0.485-inch lift), 11:1 compression, full-floating wrist pins, a forged crankshaft, and more. Because the engine did not produce much torque and had such high rpm capability beyond 7,000 rpm, 302 Z28s were only offered with four-speed transmission and were not available with air conditioning. Chevrolet also sold several cross-ram-intake setups (two staggered four-barrel Holley carburetors) and special race camshafts for the early Z28s that helped the 302 gain even more high-rpm power. With some modifications these engines would easily produce power well above 400 horses (at very high rpm).
Cylinder-head flow rates of the era were marginal at best. A typical street/strip small-block with 2.02 cylinder heads would need extensive and expensive port work to produce impressive power from the small (by today's standards) ports. Furthermore, typical cylinder head modifications did not produce good low-speed torque, so performance cars would generally need very low rearend ratios to run in the 12s. Often a 3,500-pound car with a healthy small-block would need at least a 4.56 rearend ratio or lower to run quicker than 13s. This was often the reason many hot-rodders of the era would run big-block Chevrolet V-8s. Here, the higher torque levels (from longer strokes and lots of cubic inches) would mean a 3,500-pound car could run 12s with just 3.73 gears.
Power & Adaptability
For '68 Chevrolet released a larger low-performance 307 engine as a replacement for the 283. The 307 used a 283 bore and a 327 stroke (3.875-inch bore and a 3.25-inch stroke). Production of the 307 ran until '73. By the mid-'70s, the automotive market began to change dramatically and GM sought to raise fuel economy and reduce emissions. One particular displace-ment introduced was the 305 engine (released in '76), which used a 265 bore and a 350 stroke (3.75-inch bore, 3.48-inch stroke). Other new displacements included the 262 (released in '75) and the 267 (released in the later '70s).
By the '80s, the electronic carburetor, on-board computers, and, later, electronic fuel injection helped the small-block achieve improved drivability, lower emissions, and better fuel economy. Through most of this time, the 305 small-block was used on a widespread basis in almost all Chevrolet V-8 cars. The general exceptions were some Camaros, all Corvettes, and most B-body police-package cars, which all used a variation of the 350 engine. Into the mid-'80s, small-block Chevys with factory fuel injection came with roller-lifter camshafts, one-piece rear main seals, and redesigned valve covers secured at four top center points (instead of four around the sides). In the Camaro and Corvette, tuned-port electronic fuel injection helped to significantly raise power and torque levels. By the late '80s, lower-performance Camaros and B-body Caprices received throttle-body fuel-injection systems to replace the electronic Quadrajet carburetors.
The Gen II
By the early '90s, Chevrolet introduced the Gen II small-block in high-performance cars beginning with the Corvette. First known as the LT1 and later the LT4, the Gen II featured new, low-friction internal components and reverse-flow cooling to facilitate the most powerful small-blocks since the musclecar era. When this engine first appeared in the '92 Corvette as an LT1, it developed 300 hp. This engine featured revised cylinder heads, reverse-flow cooling, and OptiSpark ignition.
The engine later became available in '93-97 Z28s and '94-96 Impala SS and police-package Caprices. In the '93 Camaro, the engine developed 275 hp (which improved in a few short years) with tuned-port fuel injection, while in the Caprice, the LT1 produced 260 hp. There are four basic differences between the Camaro LT1 and the Impala SS/Caprice LT1. First, the Camaro uses aluminum heads, as opposed to the steel on the Impala SS/Caprice. Second, the Camaro's compression ratio is 10.5:1, compared to the Impala SS/ Caprice's 10:1. Third, since the Impala SS/Caprice weighs about 650 pounds more, the computer programming is different. And finally, the Camaro's stock exhaust system backpressure is 10 inches of mercury, whereas the Impala SS/Caprice's is 13 inches. Some Gen II features, including the low profile and high-flow intake manifold, used technology that would be designed in the all-new Gen III.
Here's a look inside one of...
Here's a look inside one of today's high-performance small-blocks with roller camshafts, high-compression pistons, a custom-stroke crankshaft, and very high-flowing cylinder heads.
This Corvette Gen III LS1...
This Corvette Gen III LS1 engine has 346 ci, 10:1 compression, and an aluminum block and heads. Although it looks entirely different than the first 265 small-block, this engine is still designed with the 4.40-inch bore spacing.
The new LS6 engines (for '01)...
The new LS6 engines (for '01) produced 385 hp and 405 the following year ('02). At the time these engines boasted "performance never before seen with a small-block." Today, the small-block's advancements with 505 hp from the LS7 overshadow the LS6. Technology is always moving ahead at Chevrolet.
As noted, the ultimate factory...
As noted, the ultimate factory small-block Chevy (as of '06) is the LS7 with 427 ci, 505 hp, forged titanium connecting rods, and CNC-ported LS7-specific pattern cylinder heads. This all-aluminum engine (generally designed for the '06 Z06 Corvette) is sporadically available as a crate engine (sold through GM parts centers) under PN 17802397. Installed in a '06 Z06 Corvette, the engine will propel the car 0 to 60 mph in 3.5 seconds (all in First gear), blast through the quarter-mile in 11.5 seconds, and if there is enough room to continue up, you can expect top speeds of 195 mph. Do radar detectors work on cars like this?
The Gen III small-block was introduced as the LS1 5.7L (346ci) engine in the '97 Corvette, while Vortec versions of the Gen III for trucks were introduced in '99. This engine is configured in four displacements, 293 (4.8L), 325 (5.3L), 346 (5.7L), and 364 (6.0L). All 5.7L LS1 engines are aluminum blocks, while most other Gen III displace-ments (typically used in trucks) are cast iron. The best known is the 346, or 5.7L, and may be why many hot-rodders call all Gen III engines LS1.
The Gen III engine benefited from completely new technology (designed from a clean sheet of paper) and production methods, but even still its design drew upon more than 40 years of research and continuous improvements from the Gen I and Gen II small-blocks. Ongoing improvements on the Gen III project also supported the development of new efficiencies and power increases in the Gen IV. In many of today's modified musclecars, the Gen III/LS1 is a very popular engine swap. At the foundation is a deep-skirt, six-bolt main block that definitely has the structure to provide for a strong and dependable engine. What's especially exciting inside a Gen III are the good-flowing cylinder heads with replicated ports. Inside you'll find 2.00-inch intake and 1.55-inch exhaust valves. And if you would like to retain a carburetor, there are LS-series four-barrel carburetor manifold kits available at reasonable prices. Other good news is that used engines of this variety are beginning to surface. To help with an LS1 engine installation, lots of aftermarket companies, such as Year One, offer installation kits for musclecars, like early Camaros. GM also sells an installation book (PN 88959384) for an LS1 or LS6 going into an older vehicle.
The New Gen IV
Recently, GM introduced the Gen IV small-block V-8, 50 years after the first small-block appeared. This engine is available in V-8-equipped models of the '05 Chevrolet TrailBlazer EXT, GMC Envoy XL, GMC Envoy XUV, and in the soon-to-be-released '06 Chevrolet Monte Carlo and Impala. The new LS2 and LS7 Z06 engines are part of this engine family.
Some of these engines now offer fuel-saving Displacement on Demand (DOD) technology, and there are plans to have this feature on all Gen IV engines. This fuel-economizing feature has the capability of disabling the combustion process of half the engine's cylinders during certain driving conditions, enabling fuel savings of up to 8 percent. The process is instantaneous and virtually imperceptible, and the engine delivers horsepower and torque bands comparable to previous non-DOD small-block engines. We've driven new GM vehicles with this feature and the cylinder transition is seamless. Most recently a 6.0L V-8 version of the Gen IV engine without DOD is available in the Corvette.
Beyond the latest power numbers, the significance of the small-block Chevy has been how well GM Powertrain has continued to develop a product to surpass market demands by finding new ways to incorporate the latest technology. Just as in the past, the engine is continually positioned to reign the most hot-rodded engine ever. Something we all look forward to.
Here's what the air/fuel mixture...
Here's what the air/fuel mixture sees before entering the combustion chamber of an LS7 engine.
The LS7 uses six-bolt mains,...
The LS7 uses six-bolt mains, four in the traditional areas and two on the sides.
One of the future possibilities...
One of the future possibilities at Chevrolet is this dual-camshaft (in block) design. One camshaft is for the intake and the other is for the exhaust.
The Small-Block's Timeline
'55: The small-block V-8 is introduced in '55 Chevrolets as a 265. This is the beginning of the Gen I.
'57: 1/8-inch bore increase raises displacement to 283ci; the Ramjet mechanical fuel-injection system was introduced, bringing horsepower to 283--1 hp/ci.
'62: Displacement increases to 327ci with a 4-inch bore and a 3.25-inch stroke. Ramjet fuel-injected versions are rated at 360hp.
'64: Cylinder head improvements (2.02-inch intake valves) bump the 327's highest horsepower rating to 375 with fuel injection.'67: A little-known option called Z28 is released for the Camaro only, which includes a high-revving 302ci small-block for competition in SCCA Trans Am road racing. A 350ci (5.7L) version (in the Camaro) debuts and will become the quintessential small-block variant.
'68: A Camaro Z28 wins the Trans Am championship.
'70: 350ci LT1 debuts in the Z28 Camaro and Corvette and is rated at 360/370hp respectively; 400ci small-block is offered--the largest-displacement small-block built to date.
'75: With fuel economy prevalent in consumers' minds, a more efficient 262ci small-block is introduced. This engine, offered in the small Chevrolet Monza, makes spark plug replacement next to impossible.
'78: V-6 engine based on small-block design introduced; it would become the Vortec V-6 truck engine more than a decade later.
'80: Last year for the 400 small-block, by now offered only in light-duty trucks.
'82: Fuel injection reintroduced with the Cross-Fire Injection system on Corvette and the redesigned (third-gen) Camaro Z28.
'85: Tuned-port fuel injection replaces Cross-Fire Injection, bringing in the modern era of electronically controlled, port-injected engines.
'86: Aluminum cylinder heads debut as standard equipment on Corvette; block changed to accept new single-piece rear main seal.
'87: Hydraulic roller lifters introduced on fuel injected engines.
'89: The H.O. 350 crate engine offers a ready-built performance engine from the factory, changing the way hot-rodders approach engine-building in the next decade.
'92: The LT1 engine in the Corvette introduces Gen II small-block design, which features reverse-flow cooling, revised cylinder head design, and crank-triggered optical distributor. The engine will later be used in Camaros and will become a favorite of police officers in '94-96 Caprices with a top speed of 140 mph.
'96: The Vortec V-8 engines are introduced in trucks, featuring cylinder heads with swirl-inducing combustion chamber design to increase power and torque.
'97: Gen III 5.7L LS1 small-block introduced with all-new Corvette, featuring all-new deep-skirt block casting with six-bolt mains, redesigned cylinder heads with symmetrical ports and combustion chambers, and coil-near-plug ignition system.
'99: Gen III-based Vortec V-8 engines introduced in GM trucks; displacements include 4.8L, 5.3L, and 6.0L.
'00: The Z06 debuts with the LS6 engine pumping out 385 hp.
'05: The Gen IV small-block is introduced 50 years after the original. LS2 and LS7 are part of this engine series.
'06: 7.0L LS7--introduced in Corvette ZO6--becomes the largest, most powerful small-block ever built.