8.0:1 to 11.0:1
Induction:
2-barrel 4-barrel
Inline 2 x 4 barrel
Crossram 2 x 4 barrel
Rochester Mechanical Fuel Injection
Throttle Body Fuel Injection (TBI)
Crossfire 2 x TBI
Tuned Port Fuel Injection (TPI)
Sequential Fuel Injection with mass airflow sensor
Engine Weight:
Approximately 550 pounds cast iron ■
Abbreviating Casting Numbers
It is common to abbreviate the casting numbers when speaking or writing about them. Rather than using seven, eight, or nine digits, the last three digits are commonly used when making reference to them. Thus, a block with casting number 3970010 is referred to as the “010” block. A cylinder head with casting number 340292 is also called a “292” head. Chevrolet rarely used the same last three digits in a similar part, so there is little duplication or confusion. Some parts with the same casting number were used in a number of different model years and engine combinations. Look closely at the casting numbers and casting dates. Sometimes they are difficult to see and an 8 may look like a 3. Sometimes the last digit in a number is missing, or rust, corrosion, grease, or dirt may obscure the number. ■
If you’re looking for a serious block to use as the foundation for high output, the 350 Bowtie cast-iron block is a good start. This block (PN 12480047) is CNC machined with four-bolt mains, splayed caps, tall lifter bores, and is set up for a maximum bore of 4.155 inches. (Photo Courtesy Chevrolet Performance)
On some of the early one-piece rear main seal production blocks, the boss for the mechanical fuel pump was cast into the block. However, the holes for the fuel pump pushrod and oil drainback were not always drilled. Check your block to see if these holes exist if you intend to use a mechanical fuel pump in your application.
Not all one-piece rear main seal blocks were set up for factory production hydraulic roller cams. Some late-model Gen I four-bolt blocks used in trucks contain the one-piece rear main seal but do not have the threaded bosses in the lifter valley that are used to bolt on the roller lifter retainer. These truck blocks used a flat tappet cam and a one-piece rear main seal.
To add to the confusion, a few one-piece rear main seal production blocks share the same block casting number but may have been drilled for either two- or four-bolt main caps. The “638” casting is one example. The only sure method of determining whether you are looking at a two- or four-bolt case is to remove the oil pan and take a look.
Production Cast-Iron Bare Blocks
PN 10066034 is a Gen I, 4-inch-bore, bare block with four-bolt gray-iron main caps. This block uses a two-piece rear main oil seal and its bearing saddles are sized for cranks with 2.45-inch main journals, non-siamesed, 4.00- to 0.060-inch bores, a 9.025-inch deck height, and a wet-sump rear cap.
PN 10105123 delivers a bare, non-siamesed block with 4.00-inch bores, a 9.025-inch deck, 2.45-inch main journals, a wet-sump cap, four-bolt straight main caps, and a one-piece rear seal. This Gen I block has a lifter valley that is machined for use with either factory roller or flat tappets and respective cams. The block weighs 181 pounds. This Gen I block was used with all ZZ 350 HO and CC 350/300 crate motors and is machined in the lifter valley for a factory hydraulic roller cam. The block can accept up to a 3.75-inch stroke crank.
Chevy Performance also offers a 383-ci block (PN 88962516) with a 4.005-inch bore, which has also been clearanced for a 3.800-inch stroker crankshaft.
Maximum Bore-Size Limits
There are limits beyond which a block should not be bored. In addition, replacement pistons are sized for particular bore sizes. Oversize pistons are generally available in Standard (Std.) 0.010-, 0.020-, 0.030-, 0.040-, and 0.060-inch sizes. Other sizes are available from custom piston makers, but the sizes given here are the most common.
If you are boring a block, stay within reason. As the bores are made larger, the actual thickness of the cylinder barrel wall becomes thinner, and as it gets thinner, it weakens and is subject to more distortion. Bore the block to the minimum amount needed to clean up the walls and still retain as much barrel wall thickness as possible. This helps the barrels maintain strength and resist flexing.
Bowtie blocks come with thicker barrel walls than production blocks, so even at large overbore sizes the walls are still thick enough to withstand the racing abuse these blocks no doubt see.
Also, when a block is cast, there is a remote possibility that the casting molds shifted when the molten metal was poured in. This results in a “core shift” in the finished block. Core shift in a block can cause many problems, one of which is that cylinder walls might be very thin on one side of the cylinder and thicker on the other. Lifter bores can be off of their correct positions and cause valvetrain geometry problems.
Engine Assembly and Suffi x Codes
When an engine is completely assembled and placed into a particular vehicle at the factory, an engine assembly date code and suffix code are stamped into the block casting. Usually, this stamped code is found on a ledge on the engine block deck located at the front of the passenger’s side of the block. These codes are visible to the eye even with the motor in the vehicle, although you may have to move the alternator if it is mounted on the passenger’s side to see the block ledge beneath it. These engine assembly and suffix codes can give you a great deal of information when you decode them.
The code may look like this: F0317ZM. The F stands for the Flint, Michigan, factory where it was made. The 0317 stands for the month and day of the month, in this case the third month 03, on the 17th day. Years and decades are not given in these engine assembly codes. The letters at the end, ZM, are the engine suffix code.
Various combinations of letters were used to indicate the vehicle model type, engine size, transmission type, and other things such as air-conditioning that were used on this particular vehicle when it was made. In this case, ZM was used on a 1966 Chevy II to indicate a 327 engine, a Powerglide automatic transmission, and air-conditioning.
On some blocks, parts of the VIN are also stamped onto this ledge.
These engine assembly codes, suffix codes, part casting numbers, and other features are used to determine whether a particular vehicle is an original “numbers-matching” vehicle. Numbers-matching original vehicles are sought by collectors. Keep in mind that it is possible to fake a numbers-matching vehicle in order to increase its value to collectors. This is particularly true of rare, and therefore, more-valuable vehicles that had a low-production-number part or combination of parts. Be careful!
Also, sometimes when a block is decked during a rebuild in order to ensure flatness or to reduce the deck height, the engine assembly and suffix codes can be machined right off a small-block by an inattentive machinist. ■
Another possible problem with boring is that the cylinder barrels may have porous sections. In this case, as the boring bar cuts into the cylinder wall to open it up, it may hit a porous section. If that happens, bore to the next largest bore, if you can. If the porous section is too deep, the block may need a sleeve or have to be scrapped. If you are already at the maximum bore size, you should obtain another block and start over.
In addition, rust inside the water jackets or on the piston side of the cylinder walls can eat into the wall thickness and cause a problem when the block is bored. If you find a block that has been sitting around outside for a while, be cautious. It may have features you desire, the price might be low, or you might be doing someone a favor by hauling the block out of wherever it is, but rust can ruin the