Not long after its debut in the 1997 Corvette, General Motor’s LS-series V-8 established itself as the gold standard of performance. Sure, other engine platforms can be built to match it in terms of sheer horsepower output, but none of them offer the LS small-block’s balance of performance, simplicity, low mass, durability, compact size, affordability, and outstanding fuel mileage.
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LS blocks utilize a deep-skirt design in which the sides of the block extend all the way to the bottom of the main caps. Four bolts secure each main cap to the bulkheads, and two additional cross bolts secure each one to the side of the block. This design is extremely durable, and stock aluminum blocks have proven to be reliable up to 700 hp. (© GM Corp.)
Design Features
With the immense power potential of the Gen III design, bulking up the bottom end to meet OE longevity requirements was imperative. At the same time, engineers sought to decrease weight for improved fuel economy. The result was a deep-skirt aluminum block with six-bolt main caps and enlarged cam bores. The innovative deep-skirt design extends the sides of the block around the main caps. This effectively cradles the sides of the main caps and allows securing each cap to the block skirts using a pair of cross bolts.
In addition, engineers insisted upon enlarging the cam bores and positioning them higher up in the block. Larger cam bores can accommodate larger cam journals, which are more resistant to flex when subjected to aggressive lobe profiles and stiff valvespring pressures. With future growth in mind, the camshaft has been positioned higher up in the block as well. This increases clearance between the cam, and the crankshaft counterweights and connecting rods, making it easier to install a longerstroke crankshaft.
Despite these improvements in performance and durability, the Gen III weighs approximately 100 pounds less than its Gen I forbear while boosting fuel mileage by 10 percent. When the Gen III platform made its debut in the form of the original 5.7L LS1 in 1997, it was rated at 345 hp. That figure climbed to 505 by 2006 with the introduction to the 7.0L LS7 before being topped again by the 638 hp LS9 in 2009. Having nearly doubled in horsepower in a little more than a decade, the LS small-block’s legacy is just getting started.
single greatest contributing factor to the Gen III/IV smallblock’s outstanding power potential is its cylinder heads. In contrast to the Gen I heads that cram the two center intake ports between a pair of pushrods, LS cylinder heads feature replicated intake ports that are evenly spaced. This allows for uncompromised port geometry and excellent airflow. Stock LS1 castings flow 240 cfm, which is enough to put many ported Gen I castings to shame. (© GM Corp.)
Pushrod Power
Many casual enthusiasts measure the merit of an engine by the number of valves it has and the RPM it turns rather than by the tally it posts in the horsepower column. By those standards, with just two valves per cylinder, actuated by an in-block camshaft via pushrods, the Gen III/IV small-block is a veritable relic. However, those who know a thing or two about building engines are well aware that a highly refined pushrod design can handily trounce a poorly executed dual overhead cam (DOHC) design. Modern innovations in valvetrain technology enable pushrod engines to rev as freely as many of their DOHC contemporaries. It won’t be long before pushrod NHRA Pro Stock engines eclipse the 12,000-rpm mark, which is about 3,000 rpm more than you’d ever want to turn on the street. Combined with the staggering airflow that’s capable these days with a single intake valve per cylinder, most of the pushrod engine’s past maladies are no longer applicable. That means engine swappers can enjoy all of the advantages of a pushrod small-block without any of its past shortcomings.
Chief among the advantages are the simplicity, low cost, and compact size. Together, they make the OHV Gen III/IV small-block practical to build and extremely easy to install, even into the smallest of engine bays. In fact, LS engines will drop right into the diminutive chassis of Pontiac Fieros and Mazda Miatas without much fuss. On the other hand, positioning a pair of camshafts directly over the valves necessitates very tall and wide cylinder heads, especially on a V-8. Consequently, trying to retrofit certain domestic DOHC V-8s into an otherwise commodious engine compartment can be a huge challenge, and it often requires cutting out the shock towers.
Perhaps the most significant contributing factor to the Gen I small-block’s success and popularity was GM’s ability to mass produce it in countless iterations and displacements for a multitude of applications using one common architecture. This led to an interchangeability of components never before seen in any production motor, which reduced costs and promoted aftermarket parts development. The same applies to the Gen III/IV small-block, as the platform powers everything from Corvettes and Camaros to trucks, SUVs, and family sedans. Almost all the hardware among the different LS variants is interchangeable, and except for the smallest (4.8L) and largest (7.0L) motors in the LS lineup, all share the same 3.622-inch stroke. In most instances, the cylinder heads, camshafts, crankshafts, and intake manifolds can all be mixed and matched among different LS motors. This makes it much more appealing for aftermarket manufacturers to develop parts, promoting incessant technical innovations, an extremely diverse catalog of products from which to choose, and more competitively priced parts.
Unlike the Gen I small-block, LS-series motors were designed from the very beginning as corporate GM power plants, so referring to them as smallblock Chevys or Mouse motors is inaccurate. Since the first variant of the Gen III small-block was named the LS1, many use “LS1” as a generic name for all Gen III/IV engines. Adding to the confusion is that while Gen III and IV truck motors are usually labeled “Vortec,” they share the exact same architecture and many of the same parts as their “LS” counterparts. So whether you call them LS1s, Gen III/IV small-blocks, or LS motors, you are referring to the same great family of engines. (© GM Corp.)
The LS small-block’s castaluminum oil pan isn’t just an oil container. It serves as a stressed member of the block that helps reduce noise and vibration. Like the rest of the block, it features structural strengthening ribs on the inside and outside of the oil pan. (© GM Corp.)
Part of what made the Gen I small-block so successful was an extensive interchangeability of parts among engines with different displacements. The same is true of the LS platform. Except for the 7.0L LS7 and 4.8L Vortec truck motor, all Gen III/IV smallblocks use 3.622-inch crankshafts. (© GM Corp.)
In addition to parts interchangeability, GM further simplified the Gen III design by reducing the number of moving parts and streamlining the production process on the assembly line. For hot rodders, the result is an engine that’s even easier to assemble than the Gen I small-block. For instance, LS motors feature plates that seal the intake manifold off from the lifter valley. Not only does this prevent hot oil from splashing onto the intake and heating up inlet air temperatures, it also allows for the removal and reinstallation of the intake manifold without having to run a bead of silicone on the block. Reusable rubber gaskets integrated around each intake runner eliminate the need to replace them each time the intake manifold is removed. Likewise, removing the camshaft in a Gen III small-block can be accomplished without pulling out the lifters, as they ride in a plastic bucket that hold them into the block. Although Gen I engines have several oil passages on the back of the block that need to be plugged, LS motors use a single plate to seal them.
Explosive Potential
Thanks to the hard work of GM engineers, enthusiasts immediately recognized the untapped performance potential of the Gen III small-block. In stock trim, it frequently pushed C5 Corvettes and fourth-generation Camaros to 12-second passes down the quarter-mile. Simple cam swaps had LS1s putting out 450 hp, and stroker combos routinely produced power in excess of 600 hp. What makes these accomplishments even more impressive is that they were achieved within five years of the LS1’s launch in 1997. This was well before the first aftermarket cylinder head castings and blocks were unveiled to the public, and several years before GM introduced the big-bore Gen IV LS2. Since that time, a multitude of aftermarket manufacturers have stepped up with cylinder head and block designs of their own. Additionally, the 24-plus variants of the original LS1 that GM has released over the years means that Gen III/IV small-blocks can be built in an infinite number of configurations using both aftermarket and production parts. As deck heights keep growing, cylinder walls keep thickening, and crank throws keep orbiting farther and farther away from their mains, to make it all fit, cam bores are creeping closer to the deck, and oil pan rails continue spreading outward. To make sense of all the options at your disposal, this book’s objective is to answer the myriad questions that come up along the way with any stroker Gen III/IV engine build.
With reusable rubber gaskets that fit into the intake itself and seal each runner, the manifold can be removed and installed without having to replace the gaskets. This not only saves money, but it also eliminates the risk of blocking off the intake runners due to gasket misalignment.
In addition to superb power potential, LS small-blocks are far easier to work on than their Mouse predecessors. A lifter plate seals oil inside the lifter valley, which prevents it from splashing on the bottom of the intake manifold and heating it up. This means that the intake doesn’t need to be glued down to the block with silicone every time it’s removed and installed.
The overwhelming popularity of the LS small-block has pushed the aftermarket to develop parts at an astonishing rate. There are now several aftermarket blocks and more than a dozen cylinder head castings at an engine builder’s disposal. This crate motor from GM Performance Parts features an LSX block, forged pistons, and L92-style rectangleport cylinder heads. (© GM Corp.)
They don’t do much for aesthetic value, but Gen III/IV smallblocks have a separate coil pack for each spark plug mounted on the valve covers. This provides a much more powerful spark to ignite the air/fuel mixture, and it eliminates the need for a distributor, as the coils receive instructions directly from the engine management computer.
Fourth-generation Camaros and Firebirds are cursed with tiny engine compartments, yet it’s still possible to shoehorn a 500-ci tall-deck LS2 inside one. Even with the increase in deck height, the motor still clears the shock towers with room to spare.
As displacement figures continue to grow, the aftermarket is stepping up with serious cylinder heads that flow enough air to feed all those hungry cubic inches. These LSX-DR castings from GMPP are capable of flowing 430 cfm through the intake ports and 280 cfm on the exhaust side. That’s enough to embarrass most big-block heads. (© GM Corp.)
An interesting footnote in the development of the Gen III small-block is that the 1997 Corvette served as the guinea pig for the entire LS engine program. At the time the Gen III was conceived, GM was building more than 1 million trucks and SUVs per year, so its primary objective was to design an all-new family of engines to replace the Gen I small-block in GM’s truck fleet. First releasing the Gen III in the low-volume Corvette enabled GM to establish a performance image for its new V-8 as well as solve any potential teething issues during the manufacturing process before ramping up production. The Gen III was then introduced in GM’s truck line in 1999. (© GM Corp.)
Perhaps the ultimate validation of the Gen III/IV’s race-bred design is the new Chevy R07 NASCAR Sprint Cup V-8. Like the LS engine family, it’s a clean-sheet design that uses evenly spaced intake and exhaust ports. It also features an intake valve angle of about 12 degrees, just like in the LS7. (© GM Corp.)
First introduced in the L92, the variable valve timing system used in select LS motors can advance the camshaft up to 5 degrees and retard it up to 45 degrees, resulting in a remarkably broad powerband. It features a phaser assembly, integrated into the cam gear, that’s actuated by hydraulic pressure. With an aftermarket controller, the system is fully tunable for performance applications. (© GM Corp.)
Written by Barry Kluczyk and Posted with Permission of CarTechBooks
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