Читать книгу How to Build Killer Chevy Small-Block Engines - Mike Mavrigian - Страница 6

CHAPTER 1

THE SMALL-BLOCK CHEVY

Hot dogs, baseball, apple pie, the flag, Mom, and the small-block Chevy engine. Collectively, we’re talking about all things America. Shortly after the birth of the performance industry to the present day, the beloved SBC (small-block Chevy) continues to be one of the most, if not the most, prolific and intensely-developed, go-to engine platform in the performance and racing communities.

The first small-block Chevy engine was introduced in 1955 and was available in the Bel Air and Corvette in 265 cubic inches of displacement. Small-block engines, featuring a cylinder bore spacing of 4.40 inches, produced from 1955 to 1974 were referred to as Turbo-Fire or High Torque engines. The 350-ci engine, one of many iterations of the platform, was introduced in 1967 and helped the small-block Chevy become one of the most popular platforms for performance use. The 350 is widely considered as the standard platform for the small-block family.

The 265-ci engine debuted in 1955 and was the foundation for decades of performance that followed. (Photo Courtesy GM Media Archives)

The 1965 327-ci engine with fuel injection is shown. The Rochester Ramjet fuel injection system was first offered as a high-performance option on the Corvette and GM passenger cars in 1957. It was discontinued partway through 1965 in favor of the Chevrolet big-block as a performance option. This is a purely mechanical system, unlike modern electric systems today. (Photo Courtesy GM Media Archives)

Shortly after the debut of the small-block engine, the aftermarket began introducing components that were primarily designed to work with the OEM factory blocks to improve performance. Beginning with upgrades to camshafts, intake manifolds, carburetors, and tubular exhaust headers, hot rodders and racers began to experience and enjoy substantial performance improvements. This continued with upgraded cylinder heads in both cast iron and aluminum, forged pistons of various dome configurations, superior ignition components, stronger valvetrain components, stronger connecting rods, stronger crankshafts, stronger main caps, different crank strokes and connecting rod lengths, etc.

As racers continued to stretch the engine speed and load parameters, weak links that became apparent were quickly addressed, resulting in increasingly stronger parts in addition to components and systems that offered power enhancements. Since those early days, the small-block Chevy engine became firmly established as the standard of performance engines for street rodders, drag racers, oval track racers, and road racing competition. Aftermarket manufacturers also began producing stronger engine blocks that offered superior strength, rigidity, and cooling, in addition to providing the ability to increase cylinder bore diameters and to accept longer crankshaft strokes. In the effort to reduce weight and to improve cooling, aluminum blocks became available for specific racing applications.

General Motors continued to evolve engine platforms from the early 1970s’ LT1 and later LS-series designs to the current LT platforms, but despite this ever-evolving development of newer and more sophisticated platforms, the performance industry never abandoned the venerable Generation I small-block. It was just the opposite: development continues to this day to address the needs of enthusiasts and racers who steadfastly continue to take advantage of this engine platform.

The SBC has long been considered an iconic symbol of American performance, representing a standard to which all other V-8 engines are compared. In other words, the small-block (Gen I) Chevy engine was, and continues to be, an established workhorse and is unlikely to ever fall by the wayside. Taking advantage of all that the performance aftermarket industry has to offer, today’s builders are able to create 1,000-plus-hp beasts. One of the greatest benefits to consider is that everything you need or want is readily available. It all boils down to how much you want to spend.

Displayed is the infamous 302-ci high-winding engine that powered the iconic 1969 Camaro Z28. This engine was created in 1967 specifically to meet SCCA rules for Trans Am racing The 302 is the byproduct of dropping a 283 crank into a 327 block. (Photo Courtesy GM Media Archives)

The early small-block 265 engines featured a 3.00-inch stroke and 3.750-inch bore that produced around 162 hp and about 257 ft-lbs of torque when equipped with a 2-barrel carburetor. The 283 engine moved up to a 3.875-inch bore and increased power to 185 hp. When fitted with dual 4-barrel carbs, a higher compression ratio of 9.5:1, and dual exhaust, the power level rose to around 270 hp. In 1962, the 327-ci design debuted, featuring a 4.00-inch bore and 3.250-inch stroke with OEM power levels that reached the 340-hp level (360 hp at 11.25:1 compression in the injected Vette version). Along came the 302 engine, famous for its application in the 1969 Camaro Z28 that offered around 370 to 465 hp, depending on the intake and fuel setup.

While the basic design platform for the small-block Chevy engine hasn’t changed significantly, the performance aftermarket continues to develop components and procedures for boosting power and torque.

Thanks to ongoing aftermarket development, today you can configure a small-block Chevy for just about any application and degree of power. This example is a 422-ci build, featuring 100-percent performance aftermarket components that easily spit out over 700 hp.

Stronger and more efficient blocks, cranks, rods, threaded fasteners, and main caps have been developed to withstand today’s demands for extreme power and torque. Assembly methods have changed as well with builders paying closer attention to real-world connecting rod bolt stretch as opposed to following torque specs.

Along came the 350 small-block in 1967, and the die was cast. The 350 became the go-to standard platform for performance applications. The original crank stroke was 3.480 inches and was coupled with 4.00-inch bores. With a variety of bore and stroke combinations, cubic inch displacement choices grew. Yes, you can alter bore and stroke on any engine, but the 350 became extraordinarily popular as a basis of performance mods. The following chart provides examples of combinations.

OEM Crankshaft Journal Size

Be aware that Chevy small-block versions were initially available with different crankshaft rod and main journal sizes. Early 265 through 327 engines featured small journal cranks, while later versions featured medium journals, and the 400 version featured what is referred to as a large journal.

To provide a boost in cubic inches, and in an effort to make more torque, General Motors debuted the 400-ci version of the small-block in 1970. This block featured siamesed bores that provided more strength but reduced cooling efficiency. The bore was 4.125 inches and the stroke was 3.750 inches. The 400 crank also featured a larger 2.650-inch main journal as opposed to the 350’s 2.450-inch mains.

Weight-reduced aluminum blocks are readily available for the SBC for replacement of the OEM design as well as specialty applications and for weight savings and superior cooling.

One of the most popular engine platforms for professional Sprint car racing continues to be the SBC designed for running alcohol fuel.

CI	Bore	Stroke
355	4.030	3.480
364	4.000	3.622
383	4.030	3.750
402	4.125	3.760
408	4.030	4.000
410	4.135	3.820 (one example)
422	4.165	3.875
Note: 410 Sprint Car rules allow 410 ci with a max bore of 4.165. Various combinations of bore and stroke are used to achieve 410 ci. The above list provides mere examples of displacement combinations. Some may require the use of aftermarket blocks to achieve bore sizes not supported on factory blocks.
Also note: If you plan to increase stroke, you’re moving the big ends of the connecting rods closer to the camshaft. During test fitting, if you have a clearance concern, you’ll need connecting rods that are designed for strokers, featuring relieved shoulders above the rod cap parting line area and/or a camshaft with a smaller base circle. This is why aftermarket block–makers offer raised-cam blocks that place the cam bore higher, typically available at cam bore centerline rises of +0.125, +0.134, +0.391, and +0.434-inch.

Small Journal Cranks
CI	Mains	Rods
265	2.300	2.000
283	2.300	2.000
302	2.300	2.000
327	2.300	2.000
Medium Journal Cranks
CI	Mains	Rods
262	2.450	2.100
267	2.450	2.100
302	2.450	2.100
305	2.450	2.100
307	2.450	2.100
327	2.450	2.100
350	2.450	2.100
Large Journal Cranks
CI	Mains	Rods
400	2.650	2.100

Thanks to the research and development of aftermarket block manufacturers, we no longer need to rely on aged OEM blocks. Quality blocks, such as the Dart iron block shown here, offer superior metallurgy, improved priority main oiling, and precision casting.

In the early days, performance builders began using the 400 engine’s 3.750-inch stroke crank in 350 blocks to increase displacement of the 350, along with enlarging cylinder bores to 4.030 inches (383 ci), which required align honing the main bores to accommodate the larger 400 cranks. Also, while the 350 platform required internal crank balancing, the 400 crank required an external balance with a balance-weighted damper and flywheel.

Starting in 1998, NASCAR applications began using the SB2, which is essentially the second generation of the original SBC. The basic difference lies in the cylinder heads, which feature an altered valve layout, 11-degree valves, and an 8-bolt valve cover instead of the traditional 4-bolt pattern. A popular build involves 440 ci with a 4.000-inch stroke, 4.185-inch bores, and 15:1 compression.

Forced induction along with stronger bottom-end components raise the bar in terms of potential power. This twin-turbo SBC is a prime example.

In addition to the incredible array of components designed to enhance performance, the SBC is one of the most versatile platforms for visual customization.

NASCAR’s SB2 is essentially a small-block Chevy with different cylinder heads that feature 11-degree valves, an altered valve layout, and 15:1 compression. (Photo Courtesy GM Media Archives)

Today’s Options

Today, aftermarket cranks with a variety of stroke dimensions and choices of rod and main journal diameters are readily available for the 350 platform. This allows builders to achieve just about any displacement desired with the added advantage of superior-strength forged crankshafts. With the advent and continuing development of superior aftermarket blocks, cranks, bearings, rods, pistons, heads, cams, rockers, stronger high-grade main caps, rod and head fasteners, pushrods, intake manifolds, carbureted and injected fuel systems, and advanced ignition systems and oil delivery, the need to make do with OEM components has been eliminated.

Engine building machinery has evolved by leaps and bounds over the years in the pursuit of not only efficiency but also high-precision results from cylinder bore and lifter bore corrections to main bore sizing and alignment, bore honing, crank balancing, cylinder head seat and guide work, head porting, and beyond.

For applications that plan to use a crank-driven supercharger, small-block aftermarket cranks are available with longer, larger-diameter big-block snouts to accommodate the added stress. Many choices are available in terms of component design depending on the final goal, such as shorter-angle cylinder heads, larger valves, rocker arms of various ratios, valve springs of various metallurgy, design and rates, lightweight titanium retainers and valves, connecting rods in steel or aluminum, lightweight crankshafts with profiled counterweights, both wet and dry sump oiling systems, superior wet sump oil pumps, stronger and more precise timing systems, etc. The list goes on. There may be no other engine platform that has benefited from persistent, ongoing, and never-ending development than the stalwart small-block Chevy, and there appears to be no end in sight.

Superior ignition timing is available by referencing directly from the crank via flying magnet crank trigger systems.

The small-block, especially the 350 platform, has become, in essence, the performance industry version of a Lego set. If you can imagine it, you can build it, all thanks to the efforts of early to present-day racing engine builders and the spectacular support of the entire automotive performance parts aftermarket.

Whether for a racing application or for powering a custom street rod, the small-block Chevy remains one of the most popular choices.

The increasingly common use of CNC machining allows block blueprinting on a single machine, something unheard of in days past. Rather than consuming many hours and multiple machining operations, CNC block machining can be accomplished in a matter of minutes, with an incredible level of precision.

Despite the OEM development of current-day sophisticated engine platforms, such as the LS and LT series, the Gen I small-block Chevy engine continues to enjoy widespread acclaim and popularity for both street performance and racing applications. You simply can’t go wrong with the beloved small-block platform. It’s a true American icon.

The array of superior engine components available for the SBC is truly mind-boggling. All of today’s high-level aftermarket components evolved from the initial OEM designs to offer incredible advancements in performance and durability.