Small-Block Chevy Performance: 1955-1996

INTRODUCTION

In earlier versions of this book, we discussed the original design elements of the small-block Chevy V-8 and charted its evolution from 1955 through 1981. In this volume, we’ll expand that knowledge base and examine the engineering changes made to the small-block since 1982. The 1980s and 1990s bore witness to technical changes in the small-block, primarily designed to reduce maintenance, control oil leakage, and increase efficiency, fuel economy, and emission control through the introduction of electronic fuel injection and electronic engine management.

Chevrolet’s original success formula was basic: build the simplest engine possible. Make it the cheapest, most efficient powerplant available, and it will prevail. Project engineer Harry Barr and production engineer E.H. Kelley devoted their considerable talents—under the guidance of Zora Arkus-Duntov and Chevrolet’s chief engineer, Ed Cole—to achieving this goal. Their efforts produced elegant components such as stud-mounted rocker arms, interchangeable cylinder heads, full internal oiling, and a one-piece intake manifold that also served as a valley cover. The large-bore, short-stroke combination provided an engine that could run fast reliably and still lug a family sedan along with ease. Time has brought numerous changes and improvements to the small-block Chevy, but the basic design has proved extraordinarily resilient. In fact, prior to the early 1980s, refinements were pretty much limited to increases in displacement and whatever strengthening was deemed necessary to withstand increased power output.

Chevy thunder first rumbled in 1955 when 265-ci small-blocks turned mild-mannered Chevrolet sedans into street terrors and racetrack winners. Small-block-powered ’55 Chevys have since become one of the all-time classic cars.

Much of the engine’s success stems from initial efforts to make it easy to produce. Its compact size and light weight were crucial to the concept. Through extensive research into new thin-wall casting techniques, GM engineers produced a cylinder block casting that used fewer casting cores than any other V-8 engine. Fewer cores meant less chance for core shifting and resulting component misalignment. Through nearly 50 years of successful operation, the engine’s physical size remained unchanged, but displacement grew nearly 30 percent, and the racers made the engine produce more power than anyone ever thought possible.

The small-block Chevy grew from its original 265 cubic inches as more and more demands were made of it. Greater vehicle weight, power steering, air conditioning, and other accessories prompted increases to 283, 327, 350, and even 400 cubic inches. When various sport configurations and midsize models joined the fleet, they typically received small-block engines sized to augment their requirements. In the 1990s, the 300-hp LT1 Corvette engine featured notable changes such as reverse-flow cooling, a distributorless gear-driven ignition system, electronic engine management, and stunning performance.

All small-block Chevys through 1996 incorporate the legendary parts interchangeability that has become the hallmark of Chevy’s performance equation. 1980s-style small-block engines incorporated more design changes to cut costs and boost fuel economy. Extra thin-wall cylinder castings and lightened cylinder heads have proven less durable, and should be avoided for serious racing applications. But that doesn’t mean that there are not good pieces available for performance enthusiasts. All the necessary heavy-duty components, adapters, and hardware are available to interchange early and late small-block pieces for maximum performance and durability.

The 265-ci small-block was revolutionary in its approach to making power. Its light weight, compact size, and independently mounted valvetrain marked it for glory almost as soon as the first parts were cast.

While automakers have designed and introduced numerous new powerplants to meet the unique challenges of the 1980s and 1990s, Chevrolet continued to produce small-block V-8s in record numbers. The small-block will certainly never lack support from the high-performance and racing community that it has served so well. Virtually all types of circle-track racing in this country are dominated by small-block Chevys. Championship drag racing owes its existence to the small-block Chevy. The record books are so well covered that it is unlikely that any other engine will ever dominate the sport as completely. Small-blocks continue to perform strongly in all types of racing, including road racing, off-road racing, boat racing, and land speed record trials at Bonneville. Only Indy’s brickyard has eluded the little Chevy’s dominance.

Legions of supporters roam the streets behind small-block engines of every conceivable size and power level. Modern Corvettes and V-8 Camaros are powered by highly refined, technologically superior LS1, LS2, LS6, and LS7 small-blocks that are every bit as sophisticated as any new high-tech engine available. As long as there are automobiles, there will be small-block Chevys to power them. As long as one single crank and cylinder block still exist, small-block thunder will echo. And if the day ever comes that the last small-block Chevy is started for the last time, it will probably be a modified one.

This book covers the changes to the small-block Chevy over the years. It clearly defines the differences in small-block lineage and suggests the most reliable performance modifications available for early and late-model engines. You could build a more powerful or cheaper small-block than those presented here, but this information is documented and certified by literally thousands of racers, backyard mechanics, and factory sources. It will enable you to build a powerful, reliable small-block and allow you to join what may be the largest fraternity in the world: the fraternal order of the small-block Chevy.

Displacement Basics

The small-block Chevy has been producedinmorethanadozendifferent displacements, but the amazing degree of versatility built into the line has provided enthusiasts with the raw material to build small-blocks of virtually any displacement. Fortunately, Chevrolet engineers saw to it that each successive refinement incorporated the best features of its predecessor. As displacement increased, power and torque improved and highly stressed components were strengthened to maintain reliability. Many of these changes resulted in stronger parts that could be used to beef up earlier engines. By combining pieces from various members of the small-block family, a strong running small-block can be assembled in nearly any desirable displacement range.

Regardless of your engine’s ultimate purpose, suitable performance components are readily available. The real trick is to identify your real needs and select the pieces that will best serve them. You can accomplish this by thoroughly familiarizing yourself with the small-block’s evolution. Factory offerings are numerous to begin with, and there is virtually no end to the combinations you can derive from them. But first you have to know the players, so let’s take a look at the lineup and see what kind of depth the Chevrolet team is fielding.

The 265

Aside from an ill-fated attempt at an early V-8 in 1917, the 265 was the first production OHV (overhead valve) V-8 engine to grace a Chevrolet engine compartment. Three different versions of the 265 were offered at its debut for 1955, including a 4-bbl engine that pumped out 180 horsepower at 4,600 rpm. Engines built during that first year lacked provisions for an oil filter, and any application other than a meticulous restoration effort should avoid these blocks. Like all small-blocks, the 265 was over square, with a 3.75-inch bore and a 3.00-inch stroke. The compression ratios were 8:1 across the board the first year, but the single 4-barrel and twin 4-barrel engines offered in 1956 received a compression boost to 9.25:1. In 1957, only one 265 was offered—the 162-horsepower 2-barrel version.

The 265-ci engines oiled the lifter galleries from a metering slot ground on the rear camshaft-bearing journal. Therefore, if you install a cam without the slot, no oil will flow to the lifters and rocker arms. The best block to use when building a 265-ci engine is the 1957 version. It was used in both trucks and passenger cars and features a thicker deck surface for optimum strength and sealing capacity. These blocks were also modified to provide full pressure oiling, avoiding the oiling problems associated with earlier blocks. All 265 blocks lack provisions for side engine mounts; they can only be mounted from the front of the block.

King of the drag race small-block, Bill Grumpy Jenkins’ technical prowess has been widely acclaimed. He was a dominant force in early Pro/Stock racing with ground-pounding small-block combinations that shamed big-block and small-block racers of every brand preference.

Most recently, there was a 265-ci LT1 engine produced for use as the base powerplant in the 1993 Impala. This engine features all the high-tech LT1 innovations in a 265-ci package designed to honor the heritage of the first small-block Chevy.

The 283

When the 283 arrived in 1957, it featured an annular groove around the rear cam-bearing bore, which provided full-pressure oiling to the lifter galleries. Early 283 blocks were actually overbored versions of the good 265 blocks, and although they had the thicker decks, they still had relatively thin cylinder walls. In 1958, Chevy introduced a new block with thicker walls. It featured side engine mounts, but it’s usually considered less desirable than the 1959 and later blocks because it still used a rope-type seal on the rear main bearing. Until 1962, all 283 blocks were cast with a flat area around the base of each cylinder. When the longer-stroke 327-ci engine was introduced, this area was relieved to clear the larger counterweights of the 327 crank. Most 283s received the same treatment, which produced the possibility of building stroker motors with factory parts. You can drop in a 327 crank and revised pistons to increase the 283’s displacement to 307 cubic inches. All 283s featured a bore of 3.875 inches (0.125-inch larger than the 265) with the standard 3.00-inch stroke. The 3.25-inch stroke of the 327 crank bumped displacement to 307 ci.

The 283 was such a good base engine that it remained in service until 1968, when it was replaced by a factory-built 307. Today, 283s can be built into strong and reliable street engines or screaming drag race engines. Incredible 287-ci (.030-inch overbore) engines still power many modified drag cars, and most of them produce well over 500 horsepower.

Zora Arkus-Duntov is one of many famous proponents of the small-block Chevy engine. His contributions to the development of the Corvette and the small-block engine are legendary.

The best possible block for a 283-based engine is the 1964–1967 Chevy II block. These blocks featured thicker main bearing webs and cylinder walls, but they have become quite rare. They are easily identified by the large 62 cast on the side of the block, and the oil filter pad is recessed into a counterbore approximately 2.5 inches above the oil pan rails. The second best choice is the 1968-and-later 307 block, which has many of the stiffening features found in later four-inch bore blocks. Never use a block earlier than the 1959 piece, as all 1959-and-later blocks have neoprene rear main seal and side engine mounts. These blocks can be identified by the casting number 3756519.

The Corvette’s small-block heritage is long and strong—and powerful small-blocks still lead the charge in C-5 and C-6 Corvettes. These Corvettes feature LSI, LS2, LS6, and LS7 engines based on Chevrolet’s new Gen III small-block architecture.

Z28 Camaros have ridden the crest of small-block power to a virtually unchallenged position in the hearts of Chevy street enthusiasts. In 1993 the all-new LTI-powered Z28 fully restored the Z28’s performance heritage. Its 275-hp LT1 gave the production Z28 150-mph capability. Subsequent LSI-powered cars are capable of exceeding 160 mph in production trim.

The 327

The 327 was the first of the four-inch-bore small-blocks. This was the engine that first put real thunder in Chevrolet performance. It was introduced in 1962 and by 1966, it had been offered in several high-performance variations, including a 350-horsepower hydraulic-cam version, the 365-horsepower solid-lifter version, and the 375-horsepower fuel-injected version. The 327 became an immediate threat on the street and at the track, and it remains a capable performer today. These engines brought about the use of highly regarded big-valve cylinder heads and some surprisingly healthy camshaft and induction system combinations. Performance was the byword, and 327s led the assault.

In 1968, the 327 was updated with larger bearing journals (the same as used in the then-new 350). It was discontinued in 1970, but it will always be regarded as one of Chevrolet’s finest performance offerings. From 1962 to 1967, the 327 used the same bearing journal diameters as all other small-blocks. Main bearing journals were 2.30 inches in diameter and rod bearing journals were 2.00 inches. In 1968, the main bearing journals were enlarged to 2.45 inches in diameter and the rod bearing journals were increased to 2.10 inches. The 327 was never produced with four-bolt main bearing caps, but current four-bolt main blocks can be used to build 327-based engines. All two-bolt 327 blocks will provide reliable service as street engines and those that are not bored more than 0.030-inch over work quite well in race applications. To build a four-bolt main 327 or 327 derivative, use any of Chevrolet’s four-bolt main blocks. These are large-journal blocks, but a small-journal crank can still be used with unique thick bearings made for this application by TRW. Large journal 327 cranks are rare because they were only manufactured for one year.

The 302

The factory 302 was a racing engine in the tradition of the high-horsepower 327. It featured a four-inch bore and a three-inch stroke and was designed to place the Z28 Camaro neatly into the 305-inch (5.0-liter) displacement limit for the popular SCCA Trans-Am racing series. It used a forged three-inch stroke crank, 11:1 forged pistons, big-valve heads, solid-lifter cam, aluminum intake manifold, and Holley 4-bbl carburetor. The 1967 version used a small-journal crank in a two-bolt main block, but it was updated to big journals and four-bolt mains for 1968–1969. All 302s were fitted with the famous Duntov 30-30 camshaft (PN3849346) first used in 1964–1965 Corvette fuel-injected engines. A Chevrolet service cam (PN3927140) was used in engines actually competing in the Trans-Am series. Street engines were rated at 290 hp with 290 ft-lbs of torque at 4,200 rpm. Race engines were good for around 450 horsepower when fitted with the factory-optional dual 4-barrel cross-ram manifold and Holley carbs. Currently, a 302 can be built from any standard bore, four-inch block by using a three-inch stroke crank. They are high-revving, powerful engines, but many everyday street performance enthusiasts prefer the greater torque and flexibility from a modified 327 or 350.

The 350

In 1967, the four-inch bore block used in the 327 was treated to a stroke increase that brought about the 350-ci engine still in service today. The new 3.48-inch stroke turned the small-block into a smooth, torque-rich performer suitable for a variety of applications. Only the 295-horsepower version was available for the 1967–1968, but in 1969, a 350-horsepower version was offered. In 1970, Chevy really got serious with 360- and 370-horsepower offerings.

The ultimate 350-ci factory offering was, of course, the 370-horsepower LT1. Like earlier fuel-injected engines and the 290-horsepower 302s, the LT1 sported some serious high-performance hardware. Forged pistons, big-valve heads, and a new camshaft profile were all part of the equation. The LT1’s performance upheld the high standards set by its race-bred ancestors.

Higher-tech versions of the 350 arrived in the mid-1980s with the briefly popular Crossfire Injection and the Tuned Port Injection (TPI) L98. These engines also received the one-piece rear main seal and corresponding crankshaft in 1986. In 1990, the all-new LT1 brought the small-block to the next performance plateau with high-tech engine management and numerous improvements, including reverse coolant flow and a gear driven camshaft and water pump.

The 307

The 307 was a convenient way to extend the useful life of the venerable 283. The 283 block was factory-equipped with a 327 crank to obtain a longer stroke and more torque, which was required for hauling around intermediate sedans equipped with air conditioning and other options. The long-stroke 283-based 307 did the job and still delivered good fuel economy.

The 307 provided admirable service in late Chevrolet and other GM cars and can be successfully modified for performance use. However, the 307 is not a very popular performance engine, largely because it was not offered in a high-performance factory version. The 307’s size is confusing to many enthusiasts, and considerable money has been spent to needlessly convert a 307 to more desirable displacements. If you have a good 307 block and crank, you can use them for a street engine with considerable success. Admittedly, a racer who must build a specific displacement engine to suit class-racing restrictions may prefer a specific bore and stroke combination to achieve some small advantage. But this is expensive, often requiring special parts. For a strong street engine, practicality and economy considerations demand that you use whatever reasonable components are available. Don’t worry about exotic combinations—use what you can get cheaply or what you already have.

A twin-turbocharged 368-ci small-block built by Mike LeFevers of Mitech Engineering powered the first full-bodied sedan to run over 300 mph at Bonneville. Joe Kugel piloted the sleek Pontiac Firebird to a 300.787-mph average to steal the thunder from a handful of big-block-powered cars attempting to break the 300-mph barrier. The LeFevers-boosted small-block helped Kugel punch a 1,400-hp hole in the air to capture a longstanding milestone in land speed record racing.

The 307 was manufactured from 1968 to 1973 and there are plenty of them around. Remember that the blocks can also be used to build smaller engines by returning to the three-inch-stroke crank. All 307s used small journal crankshafts except for a rare number of large journal 1968 models.

The 400

Recognizing the increasing need for even more low-speed torque, Chevrolet updated the small-block again in 1970. By refining the internal structure of the engine, Chevy managed to achieve 400 ci from the same basic casting. Some serious changes were required to reach this displacement and still maintain reliability. The bore was enlarged to 4.126 inches, but to maintain the same bore space (4.44 inches), the cylinder bores had to be joined, or siamesed. The area between the bores is approximately 0.275 inch thick, giving the block considerable strength. These are still thin-wall castings, however, and many engine builders prefer not to bore them at all. The 3.75-inch stroke also required some changes. In order to fit everything inside the same external package, the connecting rod was shortened to 5.565 inches center-to-center. Main bearing size was increased to 2.65 inches to further improve reliability.

The 400-ci engine was produced with four-bolt and two-bolt blocks. In 1970, most 400 blocks had three core holes on each side of the block, but many of the later-model two-bolt versions had the usual two holes per side. The 400 small-block was built through the end of the 1980 model year, so check the cylinder block casting number chart included in this chapter to see what kind you’re looking at. The 400 blocks also have six steam holes drilled in each deck surface. Corresponding holes are drilled in the cylinder heads to prevent steam pockets from forming in the cooling system. If you install a cylinder head other than an original 400 head, it will have to have the holes drilled by using a head gasket for a template. Externally, the 400 is the same as other small-blocks, and all performance equipment will fit.

The 262

The 262-ci engine was introduced in 1974 and only lasted until mid-1976. With a bore of 3.671 inches and a 3.10-inch stroke, it is the smallest small-block ever produced. These blocks can be safely bored .030 inch over. They will accept minor performance bolt-ons, but are not really up to par for serious performance use.

The 305

In 1976, Chevy offered another new small-block. The 305 combined the long-stroke crank from a 350 with a 3.736-inch bore. Many shops are building mildly modified 305s that produce more torque and power while still delivering good fuel economy. They respond favorably to traditional modifications, and they can figure easily in any number of performance plans. In 1985, the 305 was equipped with tuned port injection (TPI) on high-performance models. These TPI engines can serve as the basis for strong running street engines. Throttle body injection is the standard late-model induction system for the 305. The best choice is a fuel-injected engine produced after 1984, most of which had a higher 9.5:1 compression ratio. Also keep in mind the one-piece rear main seal incorporated on 1986-and-later engines.

The small-block was treated to exotic hardware almost immediately after its introduction. It had 4-barrel carbu-retion the first year, twin 4-barrels the second year, and factory fuel injection the third year. Fuel-injected engines were