The Best Things Come In Small Packages -- The History Of -- Chevy High Performance Magazine

More Than 50 Years of Small-Block Chevys

By Bob Mehlhoff

Photography by Bob Mehlhoff, Jeff Smith, GM Powetrain

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.