These big chunks of iron or aluminum are indeed the building blocks upon which your entire engine is crafted. Oil passages, lifter bores, and dozens of bolt-hole locations all factor into what makes a good block for a true highperformance or racing big-block Chevy. Most of these machining operations have been handled at the factory, and more often than not, they are going to be right on the money. When it comes time to select your block, you want to start with the right casting for your projected power level, and then find the best machine shop Diy Boat Deck Paint Free to bring everything to spec.
The first decision you need to make when it comes to selecting a block for your bruiser is whether to start with a factory production or aftermarket block. Gen VI Bowtie block with splayed bolt billet steel main caps.
This cutaway of a Merlin III block shows the beefy cylinder walls made possible with siamesed bores. This allows much larger bore sizes than stock Diy Jon Boat Casting Deck Names blocks and the thick cylinder walls promote better ring seal. Also note the additional head-bolt bosses in the lifter valley, which give extra clamping power for a better head gasket seal. Photo Courtesy World Products.
I limit power levels to hp with a two-bolt main block. For higher power requirements, the aftermarket blocks start to look a lot better. You can get there with a stock block ci engine 4. And, you probably have to spin the engine up to about 8, rpm, which puts additional wear and stress on all components, especially the valvetrain. But a ci engine 4. And you can easily get there by using less expensive heads and a typical high-performance oiling system.
You make the power at a lower RPM, which eases wear and tear and takes less of a toll on the valvetrain. When overboring your block, the best way to determine the maximum safe bore size is to use a sonic wall thickness tester, a very expensive piece of equipment that most high-end machine shops will have on hand. The minimum safe wall thickness is. Most production blocks will easily accommodate overbores of. The best indicator of core shift during the casting process is to look at the lifter bore bosses: the lifter bores should be well centered in their bosses.
The cylinder wall thickness of Bowtie and aftermarket blocks with siamesed bores has varied considerably over the years, but most can safely tolerate bores to 4. For the amount of money being invested in an engine of that nature, you are best advised to have the cylinder walls sonically checked and hold to the minimum wall thickness of.
Always inspect a used engine for damage that is unrepairable, like cracks or excessive overboring, as well as flaws that can be fixed at additional expense, like stripped bolt-holes, main bore misalignment, and uneven deck surfaces. Aftermarket blocks, like this Dart Big M cast-iron block, may cost more than stock blocks initially but can save you money in the long run as you search for more horsepower.
Here are the specifications of the front of the block: B. Main Bore: 2. Cam Bore: 2. Crankshaft-to-Camshaft Centerline: 5. Deck Height: 9. All stock blocks are cast iron except the rare ZL-1 aluminum block, which saw limited production in Stock blocks produced from to are the original Mark IV design, and were available with either two- or four-bolt main caps, and in three bore sizes four, if you count the T talldeck truck blocks with their miniscule 3.
The had a bore of 4. All else being equal, there is no reason to start with any stock block other than the larger 4. Muscle-car era Mark IV blocks with four-bolt mains were drilled and tapped for oil cooler fittings just above the oil filter mount. These are where the main oil gallery was crossdrilled to feed the main bearings.
Standard big-block deck height is 9. You can easily spot a tall-deck block by looking at the distance from the top water pump bolt-hole to the deck surface. With a standard-height block, the top of the water pump is nearly even with the deck, but a tall-deck block has.
Very early Mark IV blocks had a couple of peculiarities you should be aware of. First, and blocks used a grooved rear cam bearing with a matching groove in the rear camshaft journal. This groove was designed to supply oil to the lifters, and if a non-grooved bearing or cam is used, there is no oil supply to the passenger-side lifters�this is not good. Second, all Mark IVs through used the s-era oil canister with an oil filter cartridge inside. The andlater engines got the traditional spin-on oil filters that we all enjoy changing to this day.
In , General Motors changed several important design features of the Mark IV big-block with the introduction of the Gen V engine, most notably the addition of a one-piece rear main oil seal, and different coolant core passages in the deck surface of the block and heads.
Gen V and Gen VI blocks are easy to spot in the wrecking yard; they all have a revised front core that features a distinctive continuous machined boss for the front cover, water pump, and front accessory mounting bosses, giving the appearance of having a frame around the front timing cover. All production engines were fuel injected by this time, so the mechanical fuel pump boss was also eliminated.
The supply of good crankshafts, oil pans, and cylinder heads would no longer fit, which limited its performance potential. Those performance challenges were addressed by a responsive aftermarket parts industry, and soon we had a choice of high-performance cylinder Diy Boat Deck Replacement 800 heads designed to work with either Mark IV or Gen V deck surfaces with the appropriate head gasket for the block being used , two-piece seal adapters allowing the use of traditional Mark IV crankshafts, and performance oil pans designed for the wider rear main cap with its one-piece seal on the Gen V block.
This block has been drilled and tapped to accept a standard bolt front cover; stock timing cover had six bolts. Gen V and Gen VI blocks feature a priority main oil gallery that runs parallel to the lifter supply oil passage on the left of the block.
They feature siamesed cylinder barrels and the finished bore size is 4. They can safely be bored to 4. For one thing, production-line Gen V blocks have no provision for mechanical fuel pumps or traditional clutch linkage. These obstacles can be overcome by using an electric fuel pump and hydraulic clutch linkage, but you have to factor in these additional expenses and see how they compare to simply buying a block that has the features you need in the first place. Also, consider the limited cylinder head availability for the Gen V deck surface.
There were very few factory performance heads made for this engine family, and these were mostly for the over-thecounter HO engine. There is a good assortment of aftermarket cylinder heads, both cast iron and aluminum, that work on the Gen V, but you have to factor in the additional cost of these premium parts. In , the Gen VI was introduced with additional changes.
Probably the easiest feature to spot when trolling for blocks at the salvage yard is the six-bolt composite or aluminum front timing cover.
If the cover is missing, just look for the six-bolt pattern, compared to the bolt pattern used on all Mark IV-style engines, including Bowtie and aftermarket blocks. Gen VI blocks also benefit from the reintroduction of the mechanical fuel pump boss and clutch pivot stud boss. This can be important if your plans call for the use of a hydraulic roller lifter camshaft, because the cost of the lifters is quite a bit more than the cost of the camshaft.
If your core engine includes the original GM roller lifters, they may be reused unlike conventional flat-tappet lifters as long as they are in good condition, although the stock lifter and guide arrangement is limited to valve lifts of around. If your block does not have the factory roller lifter alignment bosses, there are aftermarket roller lifters available with self-aligning tie bars so you can still use a hydraulic or mechanical roller cam. If you use tie-bar roller lifters, the taller lifter bores require roller lifters that are.
There is one more OEM block that was found in the last production bigblock engines used in trucks from to , and that is the 8. While General Motors is nearly mute about this engine, you could call it the Gen VII big-block, because it has substantial differences from all other big-blocks. And no, the bolt pattern is not the same as the Bowtie or aftermarket bolt pattern, both of which use two additional bosses in the lifter valley.
It is fully computercontrolled, and features a distributorless coil-near-plug ignition system and multipoint electronic fuel injection EFI. It relies upon crankshaft and camshaft position sensors, and has redesigned water pump and coolant passages. In short, it is a unique animal in the big-block jungle, and very few other bigblock performance parts fit. It does have both early- and late-model-style motor mount bosses, meaning it bolts into any engine compartment originally designed for the big-block, but its tall-deck design and different accessory mounting locations likely require some surgery with a cutting torch.
There are aftermarket sources for powertrain control modules, if you really want to tackle something different in the world of big-block engine swaps.
Another block of considerable interest to hot rodders is the , sometimes referred to as the 8. The was never installed in production vehicles, though many were used by the marine industry, especially Mercury Marine. It features siamesed cylinder barrels and a finished bore size of 4. Drop in a 4. This makes the ci block an ideal start for a moderately high horsepower street, marine, or drag race engine, but remember that it is basically a production-line block and does not tolerate large overbores.
It is not the same casting as the factory-produced highperformance Bowtie blocks. While never installed in production vehicles, General Motors Performance Parts GMPP offers several replacement four-bolt main blocks suitable for performance applications.
PN is a non-siamesed-bore block with a 4. Because it is a production-based block, bore size should be limited to 4. It is machined for the Gen VI 6-bolt front cover, but there is adequate material to drill and tap the block for use with traditional bolt covers, if desired. This production-based non-siamesedbore block with a 4. PN shares the same traits as the PN block, but has siamesed 4. This is the block that General Motors uses for all of its ci crate engines, including the ZZ Beginning in the s, Chevrolet rewarded its legion of Pro Stock and other big-block racers with the introduction of the Bowtie blocks, which have substantial improvements over regular production-line blocks in terms of strength and potential bore sizes.
The most notable of all these features was the introduction of siamesed bores, which have no water passageways between the individual cylinder barrels. The thickness of the cylinder barrels was increased enough to accept 4. There have been many versions of the Bowtie blocks, in Mark IV, Gen V, and Gen VI configurations, so the maximum bore size varies with the individual block casting number. Many can be safely bored to 4.
Mark IV Bowtie blocks still used the original oil passage design, which I like to call side-oilers not to be confused with Fords of the same name , since the main oil gallery is a drilled passage along the left side of the block just above the pan rail surface. Gen V and Gen VI Bowtie and production blocks feature a priority main oiling system, in which the main journals receive the oil before the lifter bores, ensuring that the most critical components in the engine are the first stop on the oil supply route.
These plugs cover the opening where the factory drilled intersecting holes to feed the main bearings from the main oil gallery. Another major benefit of all Bowtie blocks is the extra-thick deck surface with blind cylinder head-bolt holes. The thicker-than-stock decks are more stable under high loads, such as ultra-highcompression ratios, nitrous, or supercharged applications. Any time power production goes up, the load on the cylinder head and block junction surface increases, and the thicker decks are simply more stable and provide a better clamping force for the head gaskets.
The blind head-bolt holes require no thread sealant, and positively eliminate the ageold problem of engine coolant leaking into the engine through the head-bolt bores in the head.
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