mains, a one-piece rear seal, and clearanced for a 3.80-inch-stroker crankshaft. (Photo Courtesy Chevrolet Performance)
The 1987-and-later Gen I blocks were produced with taller lifter bores for use with factory-installed hydraulic roller cams and roller lifters with bolt bosses in the lifter valley for a roller lifter retainer spider. Flat tappet cams and lifters can be used in these blocks. The late-model hydraulic roller lifters are taller than a hydraulic flat tappet lifter and should be used with shorter factory pushrods for production roller lifters. All Gen II production engines use hydraulic roller cams and roller lifters.
Aluminum blocks weigh approximately 90 pounds bare. Cast-iron production blocks weigh about 150 pounds. The heavier Bowtie cast-iron bare blocks weigh approximately 185 pounds due to their thicker cylinder walls and decks and reinforced block webbing.
There are significant differences between the Gen I, Gen II (introduced in 1992), and Vortec small-block V-8s (introduced in 1996).
The large-diameter flywheels and flexplates (14 inches) that were used with one-piece oil pans may not fit some early engine and vehicle applications. The crossmembers and small-diameter bellhousings were originally made to be used with a 12¾-inch flywheel or flexplate. To fit the larger flywheels and flexplates, change the bellhousing or change to the smaller-diameter ones. Keep in mind that most blocks are drilled for two different starter bolt patterns, while some blocks have only been drilled for one starter mounting position.
Small-Block General Specifications
Configuration:
90-degree ohv V-8, with cast-iron or aluminum blocks and heads
Cylinders (Front to Rear):
Driver’s side: 1-3-5-7
Passenger’s side: 2-4-6-8
Firing Order (Clockwise on Distributor):
1-8-4-3-6-5-7-2 (Gen I, Gen II, and Vortec)
Computer controlled, no distributor
Crankshaft:
Gen I, II, and Vortec: Forged or cast, five main bearings, thrust on rear bearing
Crankshaft Journal Diameter:
1955–1968 small journal: Mains 2.30 inches, rods 2.00 inches
1967–1996 medium journal: Mains 2.45 inches, rods 2.10 inches
1970–1980 400 Crank: Mains 2.65 inches, rods 2.10 inches
1989-up LT5: Mains 2.76 inches, rods 2.10 inches
Crank Strokes:
Small journal: 3.0 inches and 3.25 inches
Medium journal: 3.0, 3.10, 3.25, and 3.48 inches
400 Cranks: 3.75 inches
LT5 350: 3.66 inches
Rod Length:
Forged steel 5.7 inches center to center
5.565-inch 400 rod
5.740-inch LT5 rod
5.940-inch Gen II 265-ci L99 V-8
Pistons:
Cast, hypereutectic, or forged aluminum slipper skirt design
Lubrication:
Full pressure oiling, wet sump
Some Bowtie blocks offered for dry sump
Block Bores:
3.50 to 4.126 inches
Bore Centerlines:
4.040 inches
Cubic-Inch Displacements:
262, 265, 267, 283, 302, 305, 307, 327, 350, 400
Compression Ratios:
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
