If you were building a house, you’d want to ensure that the foundation is a solid as possible before you built the rest of that multistory dream home. The same is true with engines, and that the foundation is the cylinder block. This chapter will deal mainly with the first generation small-block Chevy that includes the post-1986 modifications for the one-piece rear-main seal and hydraulic roller camshafts. We will not deal with the LT1 or LS1 engines in this book. There’s still plenty to talk about when it comes to blocks since GM Performance Parts alone offers 16 different iron and aluminum mouse-motor blocks. Add the castings from Brodix, Dart, World Products, and others, and there are dozens of variations to choose from in the world of cylinder blocks.
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Let’s start with the most basic information for the small-block Chevy production blocks. Chevy produced several blocks prior to the 350, but since these blocks do not offer much in the way of large cubic inch potential, we would refer you to one of the many other books that deal with the older small block configurations. We will concentrate on the 4.000, and 4.125-inch bore blocks that make up the bulk of small block Chevy production blocks.
The original small-block Chevy block was designed with 4.40-inch bore spacing and a deck height of 9.025-inches. This means that the block deck is 9.025-inches from the crankshaft centerline. These two dimensions deter-mine the overall configuration of the small-block Chevy. Starting in 1968, Chevy changed its crankshaft main journal diameter from 2.30-inches to 2.45-inches to increase crankshaft strength and to accommodate the larger displacement 350ci engine first built in 1967. The 350 offered this medium size journal diameter along with a 4.00-inch bore and a 3.48-inch stroke. This is by far the most populous of all the pre- 1986 small blocks. These Chevy blocks were produced in both two and four bolt main caps. These blocks can be used for performance applications of up to about 450 hp, but be forewarned that as these blocks age, they are susceptible to cracking in the lifter valley and underneath the main webs. This is especially true of the 4-bolt main blocks since the majority of these blocks were used in trucks and performance applications that saw especially rough duty. The smart move is to always have any used block cleaned and Magna flux tested for cracks before any machine work is performed.
In 1970, Chevrolet introduced a third revision to the standard small block with the 400 block. This block featured a large 4.125-inch bore that required siamesing the cylinder wall liners at the mid point, which also increased structural rigidity. This means that the outside diameters of the cylinder walls were actually joined, eliminating the coolant passage around the area between the cylinders. These blocks retained their bore spacing and external dimensions but internally the main journal diameter increased again, this time from 2.45 to 2.65 inches to support the additional load of the longer 3.75-inch stroke. These 400 blocks were built for several years, but their popularity has led to a rapid decline in the number of serviceable blocks available for performance use. 400s came in both 2-bolt and 4-bolt configurations, but ironically, in the main cap web area, the 2-bolt main versions are the stronger of the two. The 4-bolt main caps cannot be interchanged with the two-bolt main blocks. The 2-bolt main blocks offer more material in the area directly above the main webbing that was deleted for weight considerations when the 4-bolt blocks were cast.
The ideal performance configuration for a production 400 block would be to convert to a set of aftermarket steel 4-bolt main caps and drill and tap the outer two bolt holes for each additional cap. This will also require align boring the main caps to establish the proper housing bore diameter and also demands a specific two-piece rear-main seal that is offered by Fel-Pro. All of this incurs significant machine work and cost. Even if you find a standard bore 400 block that passes the crack test, you might want to seriously consider the price difference between investing considerable money into a stock production block of dubious lineage compared to the cost of a new aftermarket block. This is especially important if the engine will be intended for power levels exceeding 550 hp. For example, it’s possible to invest well in excess of $1000 in machine work alone when you consider the cost of cleaning, Magna fluxing, boring, torque plate honing, adding 4-bolt main caps, align boring, and decking the block. Conversely, you could invest in a GM Performance Parts Sportsman block that offers exceptional strength requires very little machine work to be up and running. However, this offers several advantages over a used block. The initial cost of the new block is certainly higher (around $1,800 or more), but the net result is a much stronger foundation that allows you to increase power without worrying about reliability.
1986 AND LATER BLOCKS
By 1986, Chevrolet engineers decided to address some of the small block’s inherent shortcomings that included problems associated with long-term rear-main seal integrity. In other words, that troublesome 2-piece rear-main seal had to go. In its place, GM created a round, one-piece, rear-main seal design that required a new rear crankshaft flange. This constituted the first major change in the small block Chevy block since 1955, creating two distinctly different blocks. One-piece rear-main seal cranks cannot be used in blocks designed for use with two-piece rearmain seals. However, several aftermarket companies as well as GM Performance Parts offer a rear-main seal adapter that will allow you to use a two piece rear-main seal style crankshaft in a one-piece rear-main seal block.
Initially, all performance engine buildups used the two-piece rear-main seal construction since all performance crankshafts followed the two-piece design. Recently, however, the aftermarket performance world has begun to recognize the leak-free benefits of the one-piece rear-main seal style block and crank. One advantage to the one-piece configuration occurred the next year in 1987 when most Chevy small-block production blocks (excluding trucks) were converted to hydraulic roller tappets. Again, it took time for the aftermarket to embrace this modification, but now there are many advantages to building a mild performance small block using hydraulic roller tappets and a one-piece rear-main seal. As an example, you can now easily build a 383ci small block using a castiron, one-piece rear-main seal stroker crank along with a performance hydraulic roller camshaft while retaining the stock hydraulic roller tappets and the factory retainers. This not only offers a displacement increase over a standard 355, but also reduces the cost of converting to a hydraulic roller cam. We’ll get into more details on camshafts in Chapters 7 and 8 on cams and valvetrains.
BOW TIE BLOCKS
The days of worrying if your engine would stay glued together because you are forced to use a production block are now long gone. Between the aftermarket and GM Performance Parts, there are literally dozens of iron blocks available in virtually any configuration you can imagine. The original high performance iron cylinder block from the Chevrolet was called the Bow Tie and exists today in several variations. For big cubic-inch applications, GM Performance Parts offers five different standard deck or talldeck, iron blocks that will accommodate 4.125 to 4.155-inch bore diameter.
A good deal among the large-bore Bow Tie blocks is the Sportsman block that comes in a standard 9.025-inch deck height, nodular iron 4-bolt main caps, and either a 3.986-inch or a 4.117-inch bore size that can safely be bored out to 4.155-inch for large displacement motors.
The Sportsman block differs from older production blocks since it is intended to be used with a one-piece rear-main seal style crank, rather than the more traditional two-piece-seal crank. One place where these blocks also save a little money is that they are assembled using nodular iron main caps instead of the more traditional steel caps. According to GM tech sources, these blocks will accommodate up to a 3.75- inch stroke crank, but with some minor grinding, a 3.875-inch stroke can be fitted. On advantage for all Bow Tie blocks is that the area just above the pan rail is solid cast iron, which allows grinding room for clearance in this area. Production blocks extend the water jackets into this area, drastically limiting the amount of room available for stroker cranks. Many production blocks have been ruined when the engine builder hit a thin wall casting when grinding clearance for a stroker crank.
The Sportsman block will certainly increase in popularity now that there are several companies building stroker cast and forged one-piece rear-main seal crankshafts. We will get into more detail about those options in Chapter 4 on crank shafts. Among the several different GM Performance Parts blocks available, there is also a 9.325-inch, tall-deck, castiron block. This tall-deck block increases the deck height over the stock 9.025-inch spec to allow the use of longer stroke crankshafts and longer connecting rods. This tall-deck block is the GM Performance Parts Rocket block. It features a 0.390-inch higher camshaft location that creates more clearance for the use of a longer stroke. According to Chevy, this block can fit up to a massive 4.125-inch stroke crankshaft without the need for a small diameter base circle cam. The camshaft also uses big-block cam bearing diameters, which means that the cam would have to be specially ground with small-block specs on big-block journals. The oil pan rails are also spread 0.800-inch (0.400- inch per side) to clear the longer stroke crank. Other features include a priority main lubrication path, dual starter locations, and a mechanical fuel pump boss.
Like most of the other CNC machined Bow Tie blocks, this block would require minimal machining after establishing the final bore size and deck plate honing the piston-to-wall clearance. The advantage of this CNC-machining is that GM can do quality, high-volume machining on these blocks for a far better price than if you were to have the block machined at a private machine shop. GM originally created this program to meet the demand from the factory-backed Winston Cup racers. Even so, you can expect a tall-deck block like this to require significant custom machine work in order to properly fit all the more exotic pieces that would be required to complete this type of engine. Given its race-oriented nature, you would expect this block to be very expensive, yet our latest price check through Scoggin-Dickey Performance Center put this casting at $2,600, which is reasonable given its race heritage and low volume. It’s also important to note that this tall-deck block is no lightweight. While a production iron block weighs in around 180 pounds, this Rocket block tips the scales at a hefty 202 pounds. That’s the price you pay for all that extra height.
If weight is an issue, GM Performance Parts makes that a priority with three different aluminum blocks. There are two standard deck height blocks that will accommodate 4.155-inch bores with either 350 or 400-style main bearings. There’s also a monster 9.525-inch talldeck version with 350-style mains and 8620 steel main caps. Since all three of these blocks are intended for competition use, they are configured for dry sump style oiling, which means the rearmain cap does not offer a boss to mount a wet-sump style oil pump. At 89 pounds, the stock deck height aluminum block is about as light as you can get.
GM isn’t the only game in town for high performance small-block cases. Dick Maskin’s Dart Machinery has slowly become known as one place to look for performance castings. Maskin’s decades of Pro Stock experience have taught him the value of starting with a strong, high-quality block. The result is a plethora of performance pieces that you can choose from to create your own big-inch small block. Dart offers virtually everything a street enthusiast could ask for in a big-inch case with the Little M series of iron blocks.
The Little M iron blocks are where all but the most affluent engines builders will play. Iron blocks offer the advantage of incorporating all production-based small-block parts such as camshaft, oil pump, timing chain, oil filter, motor mounts, and clutch linkage, so you don’t have to be concerned with searching out expensive, one-off, specialty parts. The most popular Little M block is the standard deck height, 4.125-inch bore, stock oil-pan rail width block, which uses either 350 or 400-style main journal sizes. You can also order your block with steel 4-bolt main caps, if that’s your preference. These blocks also offer dual starter locations so the starter can be moved to the driver side of the block for extra oil pan clearance. You can also order a Dart block with a raised cam location that still comes with a standard deck height. Despite their race nature, these Dart blocks also come with a mechanical, standard, small-block boss but requires the use of a 0.200-inch longer big-block pushrod. All of these blocks are also machined for 2-piece rear-main seals to fit standard performance cranks. You even have the option of using a chain, belt, or gear drives that are configured for the taller raised camshaft location. Dart’s specs specify an excellent 0.275-inch cylinder wall thickness minimum at a bore diameter of 4.185-inch.
Dart also offers a second line in the iron block department called the Iron Eagle block. This block incorporates many of the features found in its aluminum blocks in a more race-oriented version. All these blocks come with steel, 4-bolt main caps, as opposed to nodular-iron caps. They also feature spread oil-pan rails and a raised camshaft location with your choice of either small-block or big-block cam journal diameters. In the Iron Eagle line, options include a taller 9.325-inch deck height, a 0.391-inch raised cam location, an optional big-block cam bore size, and spread oil pan rails. You also have the option of either 350 or 400-style main journal diameters and either wet or drysump configurations.
If weight is a prime concern and you don’t mind lightening your wallet, Dart also offers an aluminum small-block casting in both standard and two different raised-deck configurations with 9.325 and 9.500-inch deck heights. The taller deck heights make it much easier to squeeze in a 3.875 or 4.00-inch crank while retaining a decent rod length. The alloy blocks employ high-strength ductile iron cylinder sleeves while offering two main bearing bore choices. Steel, four-bolt main bearing caps are standard and the block offers all the same options as the iron pieces for dual starter locations, mechanical fuel pump boss, and stock motor mount bosses. The aluminum block also comes standard with a 0.391-inch raised camshaft location and requires the use of big-block cam bearings to increase camshaft strength and reduce torsion twist. Maskin also makes a point to emphasize that Dart uses only virgin aluminum in all of its castings, which means that aluminum contaminated with sand and other impurities are not included in his aluminum blocks and heads. This feature makes the aluminum castings much easier to weld and repair, without increasing their price. It’s just another step in Dart’s quality-assurance program.
The aluminum block shaves roughly 100 pounds off the heft of a comparable iron block, and according to Maskin, there is very little loss in power for this weight savings. Generally, aluminum blocks sacrifice a small amount of power over an iron block due to a combination of increased heat transfer away from the cylinders as well as a significant amount of cylinder wall movement that inhibits piston ring seal. Maskin claims that his aluminum blocks don’t suffer those cylinder wall migration problems. The big hurtle is the price. Dart’s retail sticker on an aluminum Dart block is $4280, which puts it at roughly twice the price of its iron versions.
World Products is a major player when it comes to iron performance castings. World offers two similar castings: The Motown and Motown Race blocks. These are World’s latest effort using a stock deck height and camshaft location. The beauty of the Motown block is that even with a standard bore center to allow use of stock bolt pattern heads, Motown claims there is sufficient wall thickness to push the bore out to 4.250-inch! Combine this with a 4.00-inch stroke, and you have a 454ci standard deck height small block. Obviously, this is the largest bore and stroke you could squeeze into a standard deck height, and the ope-rant word here is “squeeze.” Several factors affect the durability of this combination, but the fact remains that it is possible now that Fel-Pro offers a 4.250-inch head gasket for this combination. Keep in mind that this large of a bore allows no freedom to enlarge the cylinder at a later date to compensate for wear. We’ll get into this combination with more specifics in later chapters, but the fact remains that you can build a monster small-block Chevy displacing big-block cubic-inches that externally looks no different than a 350ci mouse motor.
Investigating a slightly more conservative version, you could easily create a 4.155-inch bore and 3.875-inch stroke combination that will literally bolt into place with few modifications to the block to allow you to create a 420ci “little” block. If you want to push the envelope a little, you can certainly run this block out to a 4.200-inch bore and a 4- inch stroke and create a 443ci mouse, which is plenty big. Plus, there are all kinds of combinations in between. With inches like these, it is difficult not to achieve enormous torque at relatively low engine speeds, which makes street driving downright fun.
Getting back to the Motown block specifics, the cylinder walls have been substantially increased in thickness order to create a 0.250-inch wall thickness with a bore size of 4.200 on the thrust surfaces. With a 4.250-inch bore, this leaves only 0.150-inch in between the cylinders. While this is not the thrust side of the cylinder, it does contribute to cylinder wall integrity and stiffness. Just for the record, the lifter side of the left bank and the outboard side of the right bank are the thrust surfaces on any standard rotation small block. Another serious consideration is the minimal amount of material you need to create adequate head-gasket sealing. This question is probably best answered with a realistic look at the power output. With a nitrous or supercharged application, heavy cylinder pressure loads will probably create problems. However, a naturally aspirated combination at 600 hp or less should work. The real answers will come with time and experience but for now it appears to be a successful move.
Like all the other aftermarket blocks, the Motown also features filled oil pan rails and thicker bulkheads at the front and back of the block to help support the front and rear-mains. The Motown comes with nodular-iron main caps with 7/16-inch bolts, which include register pins to ensure the caps are properly located on the block. As with other performance blocks, the Motown also includes blind head-bolt holes, which means they are not tapped down into the coolant jackets. This eliminates the hassle of sealing head-bolt threads to prevent seepage past the bolts.
In addition, the Motown block offers a minimum of 0.600-inch deck thickness for increased deck integrity, which is especially important at high-horsepower output. Of course, all this strength also adds weight, contributing to the Motown coming in at a not-so-svelte, 190 pounds.
World also offers a Motown Race block upgrade that is reinforced with splayed bolts and billet-steel main caps that use 1/2-inch inboard bolts and 7/16-inch studs on the outboard. Splaying or angling the main cap bolts tends to distribute the load over a greater area, which offers additional strength.
Additional features in the race block include reinforced main web and bulkheads. The race blocks are also available with basic machining or as fully race-prepped castings complete with torque-plate honed cylinder walls. The additional strength adds another 5 pounds, taking the race block casting up to a bare weight of 195 pounds. The World Products catalog states that the block will accommodate up to a 3.875-inch stroke crank, but judicious whittling can create enough clearance to accept one of those monstrous 4-inch strokers.
THE COST OF POWER
We’ve spent a good deal of this chapter reviewing the advantages of aftermarket blocks. The advantages by now should be obvious, but the downside is, of course, the price. The going rate for these new blocks range from around $1,800 to around $4,000 for an alloy version. While this sounds intimidating, it’s worth investigating what you will spend to rejuvenate a used cylinder block. A bare minimum of machine work will include cleaning, Magna fluxing, boring and honing with a torque plate, an align hone, and resurfacing the decks. This will generally cost around $550 to $600. Add in the cost of converting to steel four-bolt main caps and the price jumps to somewhere around $1100. At this point, you have invested two-thirds of the cost of a brand new casting into a used block that offers no strength advantages.
Obviously, for roughly another $600 to $700, you will have a vastly stronger and higher-quality foundation that will offer years of durable service without worrying about whether it will be able to handle the power. The additional cost may be fiscally painful, but in the long run, investing in a quality casting is the first step in building a high-quality, big-inch small block that will deliver killer power and do it for a long time. Like most decisions in life, “you pays your money and you takes your chances.”
Written by Graham Hansen and Posted with Permission of CarTechBooks