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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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