Engine builders compare an engine block to the foundation of a house so frequently that the analogy has become a vapid cliché. There's good reason for this, however, as every component on an engine is attached to the block. The stresses of internal combustion can lead to block distortion, poor ring seal, and power loss; in more severe situations, they can actually split a block in half. Fortunately, factory LS blocks are extremely stout and can handle plenty of abuse with very little modifications. Conceived from the very beginning as an aluminum design, GM engineers employed several innovations to ensure the block's durability. When a Gen III block is placed beside a Gen I block, the improvements to the Gen III design are dramatic. Most noticeable are reinforcement ribs that run the length of the block and oil pan. Likewise, six-bolt main caps secure the crankshaft in place, and the head bolts thread into the main webs, further reducing block flex.
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As far as GM engineers are concerned, these design elements were incorporated to minimize cylinder distortion, thereby maximizing fuel economy and durability while reducing emissions. As far as hot rodders are concerned, a strong block provides an excellent foundation for making reliable horsepower. All factory LS blocks share a common 4.400-inch bore spacing, 9.240- inch deck height, and 2.559-inch main bearing diameter.
Gen III/IV small-block shares the same 4.400-inch bore spacing, 90-degree cylinder-bank angle, and .843-inch lifter bores as the Gen I engine, but the similarities end there. LS blocks have taller decks and raised cam bores, to accommodate longer strokes. The longest stroke GM ever used in a production small-block Chevy was 3.750 inches; by comparison, GM was able to stuff a 4.000-inch crank in the Gen IV LS7. (© GM Corp.)
In addition to containing the violent forces associated with internal combustion, a block must also resist the stress imparted on its exterior by the engine mounts as it rocks from side to side under acceleration, deceleration, and in corners. Stock and aftermarket LS blocks incorporate stiffening ribs between the engine mount bosses to minimize deflection.
In the past few years, we have witnessed the introduction of several iron, aluminum, and even billet aftermarket blocks. In addition to offering unparalleled strength, many of the latest aftermarket castings boast raised cam locations, spread oil pan rails, and extrathick cylinder walls that up the displacement ante and simplify the process of building a big-inch stroker motor. Nonetheless, for the average street/strip engine build, it's always tempting to try to score that perfect block out of the junkyard, and this chapter outlines what to look for. Some of the best values in engine blocks are offered directly from GM Performance Parts, as the factory uses several big-bore aluminum and iron blocks in passenger cars and trucks. Selecting the right block for your application is just step one, This chapter also outlines short-block machining procedures that are critical to every performance build.
Factory aluminum and iron blocks are easily identified by marks, cast into the front or back of the block, that denote their displacement. Shown here is a 6.2L block. Small-bore iron blocks are labeled "4.8L/5.3L," because they're used in 4800 and 5300 Vortec motors.
Getting Bored
Stroking an engine for extra displacement is a two-pronged approach that involves increasing the diameter of the bore and lengthening the stroke of the crankshaft. That said, the bulk of the displacement increase comes from installing a long-arm crank, and enlarging the bore has a less substantial impact. For instance, a 6.0L Vortec truck motor utilizes a 4.000-inch bore and a 3.622- inch stroke. Enlarging the bore to 4.030 inches, while retaining the stock stroke, bumps displacement from 364 to 370 ci. On the other hand, a stock 4.000-inch bore combined with a 4.000-inch stroker crankshaft yields a displacement figure of 402 ci. That's not to undermine the importance of a bigger bore, but its benefits play a crucial role in overall engine dynamics that go far beyond marginal increases in displacement.
As the intake valve opens, it comes closer and closer to the outer half of the cylinder wall. Consequently, air entering the bore from the intake port has a tendency to stack up against the cylinder wall, which can impair airflow. The flat valve angles used in the Gen III/IV architecture negate some of this effect, but it's an important consideration nonetheless. Although there is a point of diminishing returns, larger bores generally help deshroud the intake valves, which in turn improve airflow through the cylinder heads. Moreover, since larger bores increase the distance between the cylinder wall and the face of the valve, they enable the fitment of larger valve diameters, further increasing airflow at high lift points. Ultimately, the cylinder wall thickness and bore spacing of a block limit maximum bore size. Although the distance between a block's bore centers can't be changed, both factory and aftermarket LS blocks are offered with varying cylinder wall thickness. Generally, blocks with thicker walls that can accommodate a larger bore come with a higher price tag to match. Even so, opting for the biggest bore your wallet can afford usually pays dividends in horsepower.
With the exception of the LS7 and LS9, production blocks use powdered metal main caps. One disadvantage of a deepskirt block design is that it impedes the flow of crankcase pressure from bay to bay. To improve flow, GM designed breathing windows into the sides of the main caps.
Bolts are fine for production motors, but quality main studs are a good idea for any performance engine build. The stock bolt holes are 7/16 inch, but they can be enlarged to 1/2 inch if bigger studs are on the agenda.
Stock powdered metal main caps are remarkably strong and can safely handle more than 1,000 hp. For extra insurance beyond that point, companies, such as Pro-Gram and Callies, offer billet caps for about $500.
Factory Aluminum Blocks
A testament to the stunning pace of LS engine development, the Gen III small-block is no longer in production, and the Gen IV has already superseded it. Mechanically, the two generations of blocks are 99 percent similar, and almost every component is interchangeable between them. With the exception of the 5.3L block, the primary difference between them is that Gen IV blocks utilize siamesed cylinder walls, which can accommodate larger bore diameters.
Although GM manufactures nearly twice as many LS-series motors out of iron than aluminum, there is still a plethora of aluminum-block variants out there. Since 1997, GM has produced 5.3L, 5.7L, 6.0L, 6.2L, and 7.0L versions of aluminum LS small-blocks. One common thread among all aluminum LS blocks is their excellent durability. Although traditionalists raised on iron Mouse motors may have some reservations regarding the strength of these units, aluminum LS blocks can easily handle 700-plus hp. Many factory blocks have been pushed past that mark.
Although it's very difficult to break the stock main caps, they start moving around at the 1,000-hp mark. To combat this, LS7 and LS9 blocks incorporate a sleeve positioned inside the two inner main bolt holes.
LS1/LS6
Cast from 319-T5 aluminum using a semi-permanent mold process, the original 5.7L LS1 represented a dramatic departure from its Gen I forebear. Like most production aluminum engines, Gen III/IV small-blocks incorporate iron sleeves that are either cast or pressed into their cylinder bores. This provides a solid surface for the pistons to slide upon, because aluminum is too soft and would wear out very quickly without liners. Unfortunately, this limits maximum overbore to about .010 inch. With the small 3.900-inch bore used in LS1 and LS6 blocks, even with a 4.125-inch stroke this limits displacement to 396 ci. Prior to GM's release of the 4.000-inch siamesed-bore LS2 block, the only option for bumping up displacement beyond 400 ci was to install larger sleeves into the block. Although this allows running bore diameters as large as 4.125 inches, the sleeving process is extremely time consuming and expensive. It involves removing the stock sleeves (and sometimes portions of the aluminum block that hold the sleeves in place), heating up the block, and then pressing larger sleeves into place. Moreover, the procedure tends to distort the block, so it must be stress-relieved afterward. The biggest downside to re-sleeving a block is cost, as price of parts and labor can exceed $2,500.
The oil passages on the back of a Gen I small-block need to be blocked with an assortment of plugs. To simplify the assembly process, factory LS motors use a single block-off plate instead. Aftermarket blocks usually come with their own application-specific plates.
The dowel sleeves used on the LS7 and LS9 work reasonably well, but they are not as reliable as solid dowel pins on the bulkheads. The process of installing them involves drilling a small hole between the inner and outer bolt holes and then pressfitting each dowel into place. The cost for doing this, including an align-hone, is about $500.
Stroker cranks increase the angularity of the connecting rods as they swing from side to side in the cylinder bores. This can cause the rod bolts to come in contact with the block right below the cylinders. Aftermarket blocks have much more space in this area, but with production blocks, some metal must be removed with a die grinder to create sufficient clearance.
Stroker cranks increase the angularity of the connecting rods as they swing from side to side in the cylinder bores. This can cause the rod bolts to come in contact with the block right below the cylinders. Aftermarket blocks have much more space in this area, but with production blocks, some metal must be removed with a die grinder to create sufficient clearance.
Additionally, the specialized technique required to re-sleeve an aluminum block is not something that all machine shops can handle, and if not executed properly, it can lead to serious reliability problems. In the early days of building stroked LS1s and LS6s, re-sleeved blocks often suffered coolant leaks and blown head gaskets as a consequence of poor cylinder seal. Although a properly re-sleeved block can reliably support plenty of horsepower, GM's introduction of big-bore Gen IV factory blocks in 2005 has made re-sleeving an LS1/LS6 casting very uncommon, uneconomical, and impractical. For about the same price as re-sleeving an LS1/LS6 block, hot rodders can purchase a 4.125-inchbore LS7 block directly from GM Performance Parts. Likewise, a 4.000-inch LS2 block lists for $1,100. If you stumble upon a very cheap LS1 or LS6 core and don't plan on cracking the 400-ci mark for your stroker project, then it might be practical to build it up. If maximum cubic inches is your goal, however, there are far more reasonably priced blocks from both GM and the aftermarket.
Gen I small-blocks rely on a cam button or limiter wedged between the cam gear and the camshaft snout. This prevents the cam from moving forward at high RPM. GM started using retainer plates in the LT1 and LT4, and that trend has carried over to the Gen III/IV design.
LS2
Enthusiasts collectively rejoiced when GM launched the Gen IV LS2 block in the 2005 Corvette. Like the 400 Gen I small-block, the LS2 features a siamesed-bore design that eliminates coolant passages between adjacent cylinders. This allows for the fitting of a larger cylinder sleeve into the block, resulting in an increase in bore diameter from 3.900 to 4.000 inches. Combined with a 4.000-inch stroke, the LS2 block nets 402 ci. Increasing the stroke further yet to 4.125 inches boosts displacement to 415 ci. Although it's labeled as a Gen IV block, very little distinguishes it from the Gen III design. Changes include revised oil galleries to accommodate active cylinder deactivation, knock sensors that have been moved from the lifter valley to the side of the block, and relocation of the camshaft position sensor from the back of the motor to the front timing cover.
Adding to the appeal of the LS2 block is the fact that its bore diameter is large enough to be compatible with GM's rectangle-port L92 cylinder heads. It didn't take hot rodders long to figure out that pairing an LS2 block with L92 heads created an engine package that's affordable and easy to build with outstanding power potential. Available for just $1,100 from discount GMPP distributors, the LS2 block offers big cubic inch potential at a reasonable price. The LS2 block is also used in the L76, so it's more accurate to refer to it as a 6.0L aluminum production block. For applications that call for a re-sleeved aluminum GM block, a used LS2 is the ideal candidate, as it's the least expensive siamesed-bore block and can be found in junkyards for less than $500. Thanks to recent innovations in sleeving technology, an LS2 block can accommodate a 4.190-inch bore with a set of Darton dry sleeves, and a 4.200- inch bore with Darton wet sleeves.
De-burring the sharp edges of a block isn't a mandatory step for most street engines, but it does stressrelieve parts of the block to help prevent the formation of cracks. Fewer sharp edges also means fewer cuts and scrapes on your hands.
6.2L
In the wake of aluminum LS blocks, dollar for dollar, it's tough to beat the factory GM 6.2L unit. Taking the virtues of the LS2 block one step further, the 6.2L boasts the same siamesed cylinder wall design but with a larger 4.065-inch bore. When matched with a 4.125-inch stroke, this big-bore block brings the displacement tally to 428 ci. Throw in the fact that it can be had brand new for a very reasonable $1,400 through GMPP, and it's not surprising that the 6.2L block is one of the most popular foundations for an LS stroker motor. The block was introduced in the 2007 Cadillac Escalade's L92, but it has since been installed in LS3-powered C6 Corvettes, as well as both LS3- and L99-powered fifth-gen Camaros.
The biggest difference between the Gen IV block and the earlier Gen III block is the Gen IV's ability to support the hardware necessary for displacement on demand (DOD). This feature is used in certain LS motors to deactivate four of the engine's eight cylinders for improved fuel mileage. The system uses a lifter oil manifold assembly (LOMA) mounted in place of a standard lifter-valley plate. Four electric solenoids in the LOMA feed oil pressure to the lifters on cylinders 1, 4, 6, and 7, which causes them to collapse and stay shut as the cam lobes move across the lifters. The revised oil passages and extra space required by the LOMA prompted relocating the knock sensors from the lifter valley to the sides of the block and moving the camshaft position sensor from the back of the motor to the front. (© GM Corp.)
LS7
For those who seek maximum displacement packed in a lightweight aluminum envelope, the LS7 block is the hot ticket. By using press-fit iron cylinder liners instead of cast-in sleeves, GM was able to increase the LS7's bore to 4.125 inches. Even in stock trim, that big of a bore combined with a 4.000- inch stroke nets a big-block-like 427 ci. Stroke the block further to 4.125 inches, and you have a cool 441 ci. Further fortifying the LS7 block are doweled billet steel main caps. However, the LS7 block's attributes come with a stiff price tag, as it sells for $3,000 through GMPP distributors. Furthermore, although it's capable of supporting 700 hp, there is a risk of cracking the thin cylinder liners once that figure is exceeded. If you insist on running a 4.125-inch or larger bore in an aluminum block at that power level, a more durable alternative is to re-sleeve a 6.0L or 6.2L block with aftermarket ductile iron liners, which are nearly three times stronger than the GM gray-iron sleeves.
LS blocks feature a traditional six-bolt bellhousing bolt pattern, but with a slight twist. On production LS blocks, the bolt hole in the upper right-hand corner (arrow) is absent, and it is replaced with another hole at the very top of the pattern that's not present in Gen I blocks. Consequently, transmissions designed for either engine bolt up to both LS motors and Mouse motors, but with one of the bolts missing. Aftermarket blocks, like the GMPP LSX, typically have all seven holes drilled and tapped.
Opening up the bore not only increases displacement, it also creates extra space for larger valves and improves cylinder head flow by moving the cylinder wall farther away from the valves. In order to fit cylinder heads having large 2.165-inch intake valves, as in the L92 castings, GM had to increase the bore to 4.065 inches.
LS9/LSA
At 638 hp, the supercharged LS9 is the most powerful GM engine ever produced. To endure the rigors of forced induction, engineers determined that the thin cylinder walls of the LS7 block wouldn't meet their durability standards. The solution was to beef up the existing 6.2L block used in the L92 and LS3, whose thicker cylinder walls offered more inherent rigidity. To further reduce block distortion, the LS9 block is cast from a stronger 319-T7 aluminum alloy and features larger bulkheads. Since the Corvette ZR1 the LS9 is built to power is produced in relatively low volumes, finding an LS9 block on the second-hand market is unlikely. However, it is offered through GMPP for $3,300. LSA blocks used in the Cadillac CTS-V are very similar to the LS9, but have iron main caps instead of billet steel units. GM rates the LSA block at 100 hp less, and it sells for $2,400.
lifter assembly used in DOD engines consists of a twopiece body where the inner portion of the lifter slides inside the outer portion. During normal operation, a spring-loaded pin locks the inner body in place. When DOD is activated (left), solenoids mounted in the LOMA unlock the pin via oil pressure, and the force of the valvespring causes the inner portion of the lifter to collapse. Once DOD and oil pressure from the solenoids is deactivated (right), springs on the top and bottom of the lifter's inner sleeve push it back up, and the springloaded pin locks it back in place. It is possible to swap cams in DOD motors, as long as valve lift is limited to .550 inch. To install a bigger cam, DOD can be eliminated entirely with an LS2 lifter-valley cover and standard LS lifters. (© GM Corp.)
C5R
If money is no object, the C5R block is the ultimate aluminum GM casting. Designed for GM's factory-backed C5R endurance racing program, this block has proven its durability at prestigious venues, such as LeMans and Daytona. Although its $7,000 price is enough to make anyone gasp, that money buys a block that can safely support more than 900 hp. It's cast from 356-T6M aluminum alloy using a hot isostatic pressure process in which the block is placed in a vacuum chamber to remove porosity and contaminants, then it is pressurized at 30,000 psi with nitrogen during heattreating. The result is a block with outstanding material integrity, fatigue life, and strength. Additional reinforcement ribs are cast throughout the block to further stiffen the structure. Sharing the same deck height, bore spacing, and main journal housing diameter as other LS blocks, the C5R is fully compatible with all standard Gen III/IV hardware. It can accommodate a 4.160- inch bore, which yields 449 ci when paired with a 4.125-inch stroke. Other strengthening measures include doweled billet steel main caps and 4340 steel head studs that are included with the block.
5.3L
Although most 5.3L LS blocks are cast iron, GM manufactures aluminum versions for the LS4, LM4, and L33. Like iron 5.3L blocks, the aluminum units share the same 3.780-inch bore. Unlike its iron counterparts that can be bored to 3.900 inches, the iron liners in aluminum 5.3L blocks can only be opened up .010 inch. This severely limits displacement potential, and, therefore, these are not popular foundations for stroker builds. Furthermore, they cost nearly as much as larger-bore aluminum blocks on the used market, adding yet another reason to avoid them.
Several versions of the LS1/LS6 block were produced, but they are all very similar. GM revised the oil galleries at the rear of the block in 1999, and in 2001, new breathing holes were cast into the main webs to improve bay-to-bay flow of gases through the crankcase. (© GM Corp.)
Factory Iron Blocks
Granted, it's easy to be seduced by a lightweight aluminum block, but the factory iron castings used in GM trucks and SUVs offer the greatest bang for the buck of all Gen III/IV blocks in existence. Although they're called Vortec motors, GM's truck engines share the same Gen III/IV architecture as their LS-designated stable mates. Consequently, almost all the components between GM's car and truck motors interchange. The only drawback of iron Vortec blocks is that they weigh about 70 pounds more than aluminum castings. However, they're still 30 pounds lighter than a Gen I small-block, and that extra weight yields a substantially stronger block that's darn near indestructible. Some engine builders contend that Vortec blocks are stronger than the hallowed C5R block, and enthusiasts often push them past the 1,000-hp mark with great success. These factors have made iron Vortec blocks extremely popular in nitrous and forced-induction applications. Best of all, these iron blocks are a fraction of the cost of a comparable aluminum block, as GM manufactures twice as many iron Gen III/IV motors than aluminum motors.
For a big-inch aluminum stroker combo, it's tough to beat the value of the 4.000- inch-bore LS2 block and the 4.065-inchbore 6.2L block. Both can accommodate well over 400 ci, and their big bores make them compatible with the latest deepbreathing factory and aftermarket cylinder heads. The LS2 sells for $1,000 through GMPP, and the 6.2L block is listed at $1,400. (© GM Corp.)
GM builds iron Vortec motors in 4.8L, 5.3L, and 6.0L configurations. The 6.0L block—used in the LQ4, LQ9, and LY6—is the most popular with hot rodders. It features a 4.000-inch bore and can be purchased brand new for $800. It can safely accommodate a 4.030-inch bore and is good for 421 ci when matched with a 4.125-inch stroke. Even so, many hot rodders opt to stick with the standard 4.000-inch bore, which leaves plenty of meat on the cylinder walls for future rebuilds. Most aluminum LS blocks, on the other hand, don't offer this luxury. Further enhancing their value, careful shopping in local junkyards or online can uncover complete second-hand 6.0L long-blocks for $1,000, which is a fraction of the cost of an aluminum LS motor.
Thanks to the LS7's capacious 4.125- inch bore, GM was able to fit the engine with monstrous 2.200-inch intake valves. That large bore comes at the expense of cylinder wall thickness, so if plans call for re-sleeving a factory aluminum block, the LS2 casting is a more affordable alternative. (© GM Corp.)
The billet steel main caps used on the LS7 block have enlarged windows for improved crankcase ventilation, which GM claims reduces pumping losses. GMPP was so pleased with their performance that the company emulated their design in the LSX block. (© GM Corp.)
For budget-oriented hot rodders who aren't concerned with maximum cubic inches, the 3.780-inch-bore iron block used in 4.8L and 5.3L Vortec engines is an ideal foundation for a low-buck build. Although the block's small cylinders may seem like a huge drawback, they have sufficient wall thickness to open them up to 3.900 inches. That means that the block is compatible with a plethora of off-the-shelf standard-bore LS1 pistons, and it can net 396 ci when combined with a 4.125-inch stroke. Complete 4.8L and 5.3L long-blocks sell for $500 on the used market, and bare blocks can be had for even less. Considering that GM manufactures more 4.8L and 5.3L Vortec motors than any other LS small-block, junkyards will be stocked with these value-priced gems for a very long time.
Aftermarket Blocks
As good as production GM blocks may be, there's a practical limit to how much horsepower and displacement they can support. The need for aftermarket Gen III/IV blocks came early on, as the incessant progress in cylinder head technology meant that block rigidity and a lack of cubic inches were often the limiting factors in power production. Fortunately, companies, such as World Products, Dart, and GM Performance Parts, have all stepped up with aftermarket blocks of their own.
Some of the features aftermarket blocks typically offer include improved casting strength, larger crankcases, extrathick cylinder walls, priority main oiling passages, longer cylinder sleeves, raised camshaft bores, and taller deck heights. All of that equates to extra clearance for moving parts, enhanced durability, and greater power and displacement potential. Some blocks also have provisions for two extra head bolt holes around each cylinder—at the 12 o'clock and 6 o'clock position—for improved clamping force and gasket seal when used with six-bolt cylinder heads. Furthermore, aftermarket blocks are typically decked and alignhoned prior to shipment, so the only machine work they require are boring (if desired) and a finish hone. In essence, this allows spending your money on hardware instead of labor. For LS engine combinations approaching 500 ci and producing well over 1,000 hp, an aftermarket block is the ideal foundation to hold everything in place.and gasket seal when used with six-bolt cylinder heads. Furthermore, aftermarket blocks are typically decked and alignhoned prior to shipment, so the only machine work they require are boring (if desired) and a finish hone. In essence, this allows spending your money on hardware instead of labor. For LS engine combinations approaching 500 ci and producing well over 1,000 hp, an aftermarket block is the ideal foundation to hold everything in place.
Some people scratched their heads when GM revealed that the LS9 would be smaller in displacement than the LS7, but engineers determined that the LS7's cylinder walls were too thin to support 638 hp and survive rigorous factory durability testing. The solution was to go with a smaller 4.065-inch-bore block, which allowed for thicker cylinder walls. (© GM Corp.)
LSX Bowtie
Designed with the help of NHRA Pro Stock legend Warren Johnson, the GM Performance Parts LSX Bowtie block supports more than 2,500 hp and lists for $2,200. This rugged iron casting can accommodate a 4.250-inch bore and is available in either a 9.260- or a 9.720- inch deck height. The short-deck version can swallow up a 4.250-inch stroke, and the tall-deck version can handle a 4.500- inch stroke, which yields displacement figures of 482 and 511 ci, respectively. Like the LS7 block, the LSX is equipped with doweled billet steel main caps. Other tweaks include a beefed-up cam tunnel, two additional head bolt holes per cylinder, and a priority main oil galleries that sends oil to the main bearings before the lifters and camshaft. In comparison, the stock oil routes oil to the cam and lifters before the mains.
In the LS family, the Vortec 5.3L aluminum block is often considered the least desirable block for a stroker. It works just fine in the stock vehicles for which it was designed, but its thin cylinder sleeves and tiny bore diameter make it a poor choice as a foundation for a stroker motor. (© GM Corp.)
Because producing thousands of horsepower often requires very specialized hardware, the LSX can be adapted for such uses accordingly. Integrated mounting holes allow for the attachment of a front motor plate to the block, and the lifter bores can be enlarged to 1.060 inches for bronze bushings or larger lifters. Likewise, the cam tunnel can be bored out to accommodate a 60-mm cam core, and the head bolt holes can be enlarged for .5-inch studs. Additionally, the front oil feed holes can be blocked or restricted for improved lubrication when running a mechanical cam, and the front of the block can be machined for fitment of a belt-drive timing set.
For maximum end user flexibility in tailoring bore-and-stroke dimensions, the LSX block leaves the foundry with a 3.880-inch bore. This allows engine builders to bore the block out to their desired diameter. That said, GMPP also offers two short-deck versions of the LSX block that come fully bored and honed. These units are available in either a 4.065- or a 4.185-inch bore, and they are decked to 9.240 inches. Compared to a production casting, the only downside to the LSX is weight, with short-deck blocks tipping the scale at 225 pounds and talldeck units coming in at 250 pounds. On the plus side, if you're making enough horsepower to warrant such a rugged block, a few extra pounds won't hurt performance much at all.
RHS
Many hot rodders were taken by surprise when a company best known for manufacturing aftermarket cylinder heads announced that it was developing a new block casting, but Racing Head Service's LS race block is a very impressive piece of work. Weighing in at 119 pounds, just a hair more than a production LS7 block, the RHS aluminum casting offers exceptional strength in a lightweight package.
Although the company doesn't publish an official horsepower rating, its LS race block has proven to be reliable in engines producing more than 2,000 hp. Available in both 9.240- and 9.750-inch deck heights, the RHS block is cast from A357-T6 aluminum and is extensively reinforced with structural ribbing throughout. Although its maximum bore size is limited to 4.165 inches, the talldeck version features 6.380-inch-long sleeves, which can accommodate a 4.600-inch stroke and 501 ci. The standard-deck RHS block uses shorter 5.870- inch cylinder sleeves, but it can still support up to 449 ci. For easier fitment of long-stroke cranks, the RHS block has notches cut into the bottom of the crankcase for extra rod bolt clearance, and the cam bores are raised .386 inch. In addition to utilizing priority main oiling, the side oil gallery has been relocated to the outboard of the block. This not only provides extra rod clearance, it also makes it easy to plumb up a dry sump oil system, as the passage is tapped for -12AN feeds.
When it comes to sheer strength, the Vortec 6.0L iron block is the best value among all stock and aftermarket blocks, period. Because the Gen III block was originally designed as an aluminum casting, it features extensive reinforcement ribbing to reduce deflection. Cast that same design in iron, and the result is a block that weighs 70 pounds more but can support more than 1,000 hp. At high power levels, iron blocks typically offer superior ring seal than aluminum blocks. Best of all, a secondhand Vortec 6.0L block can be had for less than $500. (© GM Corp.)
Bolstering the block's competitionworthy resume are cam bores that can be enlarged to 60 mm, lifter bores capable of accommodating 1.060-inch lifters, billet steel main caps, and provisions for sixbolt cylinder heads. RHS includes ARP main studs with its race block, and, if necessary, the main stud holes can be opened up to .500 inch. To reduce windage, the main cap windows have been revised, and like the LS9 block, the RHS unit can be fitted with piston oil squirters. Well aware that the RHS block would appeal to both street/strip enthusiasts and hardcore racers, engineers fitted it with mounting holes compatible with Gen I/II– and Gen III/IV–style mounts, as well as a motor plate. A casting of this caliber doesn't come cheap, and the RHS block lists for $4,900. It's available as a 4.100-inch bore that requires both boring and honing, a 4.120- or 4.160-inch bore that needs only finish honing, or a completely machined unit in 4.125- or 4.165-inch bores that are ready for final assembly right out of the box.
One of the biggest advantages of aftermarket blocks over production blocks is their spread oil pan rails. This enables them to swallow up long strokes without a builder's need to grind them for clearance. Even with a 4.500-inch stroke, the connecting rods clear this RHS block with room to spare.
World Products Warhawk
For decades, World Products has been churning out premium aftermarket blocks, so it was only natural for the company to enter the LS market. The Warhawk block is cast from 357-T6 aluminum in both 9.240- and 9.800-inch deck heights. Tipping the scale at 133 pounds, it provides hot rodders with yet another lightweight alternative for big cubic inches.
With a maximum bore of 4.155 inches, the standard-deck Warhawk can accommodate a 4.125-inch stroke, and the tall-deck variant can be stroked to 4.500 inches. This yields maximum displacement figures of 447 and 488 ci, respectively. Like most aftermarket blocks, the Warhawk employs priority main oiling, doweled billet steel main caps, and two additional head bolt holes per cylinder. Furthermore, Warhawk's cam bores can be enlarged to 60 mm, and its crankcase is pre-notched for up to a 4.250-inch stroke. In order to stay together at the 1,500-hp level at which it's rated, the Warhawk block has substantially stronger cylinder walls than those on stock blocks. Its perimeterbased water jacket design utilizes a .080- inch-thick ductile iron sleeve (at 4.125-inch bore) that's surrounded by .300 inch of block material. A production LS7 block uses .070-inch-thick sleeves encased in .170 inch of block material. The Warhawk block is available in unfinished form with 3.990- and 4.115-inch bores and lists for $4,500. World Products also offers fully machined versions in 4.000-, 4.030-, 4.125-, and 4.155-inch bores with prices starting at $4,900.
At 250 pounds, the iron GMPP tall-deck LSX block is no lightweight. The benefit of all that bulk is that it's arguably the strongest aftermarket block available. It can handle more than 2,500 hp, and its thick cylinder walls can be bored to 4.250 inches. (© GM Corp.)
ERL
One of the most unique blocks on the market is ERL's Super Deck II LS2. The company starts out with a factory LS2 casting, attaches slugs of billet aluminum on the deck surfaces, then re-sleeves the block with Darton ductile iron liners. This increases deck height from 9.240 to 10.200 inches, which allows for fitment of a 4.500-inch stroke. Combined with a maximum bore of 4.200 inches, the combo yields 500 ci. From a reliability standpoint, wedging a deck plate between the block and heads seems crazy, but the setup has proven to be extremely robust and durable in race applications exceeding 2,000 hp. ERL cut its teeth developing tiny four-cylinder import race motors, many of which produce more than 1,000 hp, so it knows a thing or two about creatively modifying production blocks with deck plates for extra cubic inches.
Darton sleeves that are three times stronger than stock ones and ERL deck plates that cradle them in position are what make pushing that much power through a modified production block possible. The deck plate's design applies clamping pressure right at the top of the cylinder sleeves, instead of the deck surface, and the head bolts are torqued down. This directs pressure to a smaller surface area, which results in greater clamping force. The truss design of the deck plate also transmits loads below the deck surface and between the cylinder bores. Additionally, ERL opens up the head bolt holes to .500 inch, adds dowels to the main bearing bulkheads, and replaces the stock iron main caps with billet steel units. The result of all this is an extremely strong block with excellent strength and head gasket seal. For heavyduty forced-induction applications, the company recommends running a smaller 4.125-inch bore for added cylinder wall thickness.
Like many competing blocks, the LSX block has two additional cylinder head bolt holes surrounding each cylinder. Some aftermarket heads have bosses that mate up with the two extra holes, but production heads do not. That's not a problem, because it's not mandatory to use the additional holes, and production heads will still bolt up. Another option is to weld tabs onto production heads so that they mate up with the bolt holes.
The Super Deck II system is sold as a complete turnkey short-block assembly for $14,900. If you provide your own LS2 core, ERL will knock $1,000 off the total. That price includes an ERL block, Callies crankshaft, full internal balancing, Wiseco pistons, rings, bearings, billet main caps, main studs, bushed lifter bores, intake manifold adapter plates, longer head studs and pushrods, and a cam custom ground to your application. All you need to add are cylinder heads, an intake manifold, and an oil pan. ERL offers bore sizes ranging from 4.000 to 4.200 inches and will tailor compression to whatever ratio you chose.
Dart
Without question, Dart's billet-aluminum LS block is the most fascinating and exotic on the market. It's whittled down from a single slug of solid 6061 billet aluminum into the shape of a Gen III/IV block. This equates to a block that's as strong as 7075 aluminum but with an elongation rating that's five times greater than cast aluminum. Since the Dart block is CNC-machined instead of being built from a casting mold, it can be customized in any size deck height, bore, cam tunnel, lifter bore, and main journal housing you need. With the ability to support in excess of 3,000 hp, this block is obviously intended for only the most extreme applications where low mass is paramount and cost is no object. Consequently, depending on how it's optioned, the Dart billet LS block ranges in price from $7,000 to $9,000.
The RHS block boasts exceptional strength in a lightweight aluminum package. For the ultimate in quality control, RHS inspects all of its blocks by using a CT scan prior to shipping them.
The tall-deck version of the RHS block has very long 6.380-inch sleeves, which can accommodate a 4.600-inch stroke. The bottom of the cylinders comes pre-notched for extra rod bolt clearance. This very much epitomizes the concept of spending money on hardware instead of labor.
Like most aftermarket blocks, the RHS casting has raised cam bores that can be enlarged to 60 mm. The benefit of bigger cam tunnel bores is twofold. First, it allows grinding a cam on a larger-diameter core to reduce cam flex in high-RPM, highvalvespring- pressure applications. Second, it also provides extra space to fit cams with lots of lobe lift.
Machine Work
Bolting premium bottom-end components to a block with shoddy machine work is the best way to ruin the stack of parts. Although proper parts selection is critical in making sure your stroker combo hits your performance objectives, quality machine work is equally important. Consequences of poor machine work range from excessive oil consumption to compromised durability to reduced power production to catastrophic engine failure.
The World Products Warhawk block is cast from 357-T6 aluminum and weighs 133 pounds. It's offered in 9.240- and 9.800-inch deck heights in a variety of bore diameters. The company rates the block at 1,500 hp. (Photo Courtesy of World Products)
In essence, paying a machinist's bill constitutes laying out cash for labor, as opposed to a tangible product, so enthusiasts are naturally hesitant to do so. However, trying to pinch pennies during the machining phase of a stroker build can sentence the engine to doom before the assembly process begins. There's a good chance that the least expensive machine shop in town doesn't perform the best work, but on the other hand, there are no guarantees that a stiff machining bill buys quality. That's where the experience of your local hot rodding community comes into play to help steer you to a reputable shop. Naturally, knowing what the different machining procedures entail helps you determine which ones are necessary for your engine build, and make paying for them more palatable.
Block Preparation
Aftermarket blocks, brand-new production blocks, and used production blocks all have different machining needs. If you are simply freshening up a motor that you know is otherwise in good shape, or you are starting out with a brand-new block, you can immediately jump into more major operations, such as boring and decking. However, if you've rescued your block out of a junkyard, having it checked for cracks is imperative, unless you're not phased at the prospect of spending thousands of dollars machining a piece of scrap. Two inexpensive, effective ways of ensuring a block is fissure-free are magnafluxing and pressure testing. Magnafluxing involves soaking the block in a luminescent solution that reveals cracks under florescent light. Likewise, sealing off the water jackets and pressure-testing the coolant passages can find internal cracks and porosity issues not easily visible through magnafluxing.
The ERL Super Deck II block starts out as a stock LS2 casting. ERL then removes the stock cylinder walls, presses in a set of Darton wet sleeves, and caps them off with a billet aluminum deck plate that increases deck height to 10.200 inches. ERL perfected this nifty trick on small-displacement fourcylinder import drag motors.
In addition to increasing deck height, the ERL deck plate also reinforces the top of the cylinder bores. Although some may question the durability of a block based on a stock LS2 casting, the Super Deck II has held up just fine in many race motors pushing close to 2,000 hp.
Most factory iron LS blocks can safely handle a .030-inch overbore, and the sleeves in stock aluminum blocks can typically be bored .010 inch without a hitch. Nonetheless, factory casting procedures aren't perfect, so sonic checking the cylinder walls for adequate thickness is always a good idea, especially with blocks that have already been overbored. By sending sonic waves into the bores with a handheld probe and reading how quickly they reflect back, sonic checkers can determine thickness at any given part of a cylinder wall. The most important areas to check are the major thrust surfaces, which are the inboard wall on the driver-side bank of cylinders and the outboard wall on the passenger side. Aftermarket manufacturers publish maximum-recommended bore diameters for their blocks that should not be exceeded, but since some hot rodders will always roll the dice and try, sonic checking is mandatory for those who choose to ignore their advice.
Once you've determined that the block is solid, giving it a thorough cleaning will not only make it look nice, but make it easier to work on, as well. The most common method of cleaning a block is hot tanking, which submerges or pressure washes the block in a high-alkaline caustic solution to dislodge grease and grime. Most of the time, it works reasonably well, but it doesn't always completely clean water jackets, carbon deposits, rust, or scale in extremely wellworn blocks. In such instances, thermal cleaning—where the block is baked to roughly 700 degrees to burn off all impurities—is a more effective alternative. The next step in thermal cleaning involves media blasting the block to remove all carbon, which also stress-relieves the block. Finally, the block is tumbled to remove all the metal shot, leaving behind a raw cast-iron finish.
Boring
As the miles tack onto a motor, cylinder walls wear out to a shape that's no longer perfectly cylindrical. Fortunately, just about every production block is cast with additional material that can be enlarged, or bored out, to square up the cylinders once again without compromising the block's integrity. Since factory aluminum LS blocks have relatively thin cylinder liners, it's often more practical to simply hone them out .005 inch. Likewise, factory production blocks don't require a cleanup bore and are ready to run after a quick hone job. Aftermarket blocks, on the other hand, come in several different configurations. Some only need a finish hone, others come ready to run out of the box, and unfinished castings have undersized bores that can be enlarged to the size an engine builder desires.
Raising the deck height requires longer head studs, which ERL includes with its blocks. The bolt holes are also enlarged to .500 inch.
Boring out a block isn't overly complicated, but it still requires good equipment and a skilled set of hands. A boring bar is only as good as its operator, and regardless of whether or not a block is set up straight in the fixture, it bores a hole straight down. With older machines that register off the deck surface, it's critical to check that the surface is completely flat before boring begins. Although there's nothing wrong with them, they do have a higher margin for error. The preferred method is to use a boring machine that registers off the crankshaft centerline by attaching it to the main bearing bores. This ensures that the cylinder bores are perpendicular to the crank.
Cylinders are typically bored to within a few thousandths of an inch of their final bore size, and then they are honed to spec. The Rottler FA boring bar is one of the most popular units in the industry, and the most critical step in the procedure of setting it up is centering the boring bar arm inside the cylinder wall. This is accomplished by equalizing the gap among three fingers that extend from the bar with a feeler gauge. To set the width of the cut, a very precise indexing tool is used to set the depth of the cutter.
Honing
Boring cleans and straightens cylinder walls by removing material, but honing smoothes the bores to provide a smooth surface for the pistons and rings to ride on. The final finish allows the rings to seal properly and also determines the amount of friction exerted on the reciprocating assembly.
Generally, racers, in search of marginal gains in horsepower, prefer a supersmooth finish to reduce ring drag. However, this isn't necessarily the best approach for a street engine. Although a honed bore feels smooth to the touch, the finish is actually a series of fine peaks and valleys. Because the valleys retain the oil, smoother finishes reduce the depth of the valleys. Most engine wear occurs on cold starts, so street motors that experience routine heat cycles need to sacrifice a bit of smoothness in the name of longevity. This is where your machinist's experience comes into play, as the grit of stones he uses is determined by your motor's intended use.
Because the cylinder banks are situated at a 90-degree angle, moving the heads upward also moves them farther apart from each other. To compensate for this, ERL provides billet adapter plates that fill the gap that would otherwise exist between the cylinder heads and the intake manifold.
Once considered exotic, but common practice nowadays, is the process of bolting a torque plate to the deck surface while honing. The process simulates the distortion a block experiences when a cylinder head is bolted into place, and it is just another measure used to make sure the bores are as round as possible. Another procedure that is becoming more common during street motor building is plateau honing, or honing in multiple stages. As the name suggests, an initial coarse honing stone is used first, and several finer grit stones in different stages follow to flatten the peaks in the finish. The result is a smooth surface with deeper valleys that improve oil retention and lubrication for the pistons and rings. Almost all performance engines these days are plateau honed, and machinists tend to be somewhat secretive about what grit stones they use, which vary from shop to shop.
Unlike most blocks that are cast from molds, Dart's 6061 billet block is CNCmachined from a single block of billet aluminum. As a result, its critical dimensions can be sized into just about any configuration.
There is still some debate, however, regarding hot honing. It involves heating up the honing oil to roughly 200 degrees to simulate the expansion a block experiences at operating temperature. As with the use of torque plates, the idea is to get the bores as round as possible, but the jury is mixed regarding whether or not it provides any benefits.
Decking
To promote proper cylinder head sealing, the deck of the block is often surfaced, or decked, to provide a smooth, even surface for the gaskets and cylinder heads to clamp down upon. As with boring, it is critical that the deck is machined perpendicular to the crankshaft centerline. Because the pistons sit below the deck at TDC in most production blocks, the deck height is often reduced to improve quench and raise the static compression ratio. If plans call for potentially re-using a block for future rebuilds, the pistons should be left a few thousandths of an inch below the deck surface. This leaves adequate material for subsequent decking procedures.
The rate at which the boring bar cuts depends on how much metal is being removed at one time. With a larger overbore, the bar descends more slowly than with a smaller overbore, and viceversa. Boring a block .030 over typically takes 40 minutes.
For many years, the Sunnen HBS- 2100 has been the industry standard fixture for decking blocks.
The decking process begins with placing the main bearing bulkheads of a block on a bar of square-tube steel. Before any cutting begins, a dial gauge is run across the surface of the deck in numerous spots to make sure it's completely flat. Positioning the cutting head into place requires a delicate touch and lots of experience. It is lowered until it just barely touches the deck surface, and then the machine goes to work.
Align-Boring and Honing
The basic principles of align-boring and honing are similar to those of standard boring and honing, but for main caps instead of cylinder walls. There is a big difference. Overboring a cylinder is a common rebuild procedure, but because the crank rides on a set of bearings, only blocks that have been severely abused or have spun bearings require align-boring. The process entails removing material from the mating surface of the main caps, torquing them down to spec with the crankshaft removed, boring out the main saddles to within a few thousandths of an inch of the proper inside diameter spec, and honing them the rest of the way. This ensures that the main bearing bores are consistent from cap to cap and eliminates crank binding.
During the honing process, it's standard practice these days to bolt a torque plate to the deck surface to simulate the stress the cylinder heads and bolts exert on the block. Based on bore size and cylinder length, the machinist can set the rotational rate and the dwell rate of the honing shaft. It's hinged on a series of universal joints to position it straight within the bore. During the honing process, the machinist allows the block to cool every 10 to 15 minutes to prevent it from distorting.
The first step in honing involves shimming the stones for the final bore size. For the ultimate in precision, a machinist can choose among different grit stones, depending on the finish desired.
During the decking process, the rotational speed of the cutter and the rate at which the cutter moves across the deck from front to back are manually adjustable. After each swipe, a dial gauge is used to track progress, and the entire process takes about an hour.
The main caps in most production LS motors aren't held in place with dowel pins, so they tend to shift over time. Even so, used blocks that haven't endured much abuse typically only require align-honing, and many machinists also like to align-hone new blocks.
Align-boring is accomplished with a Sunnen boring fixture that attaches to a Sunnen CH-100 honing machine. They are the industry standard for align-boring and honing. The fixture can be configured to match the bellhousing bolt pattern of just about any motor, and the boring bar slides inside a pair of sleeves that sit inside the front and rear mains to ensure straightness. The bar spins at a set rate, and the machinist manually applies pressure to determine how quickly the caps are bored. The depth of the cutter is set by measuring off the block side of the mains, and the caps are bored in multiple stages until they're .0025 inch from the final main bore diameter. The process usually leaves strips of shrapnel along the edges of the caps that must be carefully chamfered off with the cutter. The more contact a bearing has with the mains, the more heat it can dissipate into the block, so a smooth, even surface is very important. The operator adjusts the tension of the stones with a thumbwheel, and he can increase pressure in small increments to slowly attain the desired final diameter. The process typically requires 1 to 11 ⁄2 hours, and if done correctly, the parting line between the cap and block will hardly be noticeable.
Written by Barry Kluczyk and Posted with Permission of CarTechBooks
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