Small Block Chevy Build
Article by Mark Trotta
All classic V8 engines had performance potential, but early Chevy V8s had more performance potential right out of the box. This was largely due to it's already good breathing characteristics, coupled with the availability of good factory and aftermarket performance parts, such as carburetors, camshafts, headers, and intake manifolds.
Introduced in 1955, Chevy's small-block V8 was an instant hit with hot rodders. 60+ years later, the Gen-One small-block Chevy is still a top choice for hot rods and performance cars.
The first SBC had a 265 cubic-inch displacement, bored out to 283ci in 1957. In 1962, the 283 was bored and stroked to produce the 327 engine.
Early blocks had an oil filler tube in front of the intake manifold. There was no PCV system, instead, there was a draft tube in the lifter galley.
Early Valve Cover Differences
The first two years of Gen-One small-blocks (1955-1956) had a slightly different valve cover bolt pattern than later (1957-1985) engines.
Note that the two upper bolt holes (shown on right cover) are slightly closer together than the bottom two bolt holes (left cover).
Up until the late sixties, small block valve covers had no holes for breather caps or PCV valves.
One of the Chevy small-block's strong points is the cylinder head design. Even original, non-modified heads from the 1960's (in good condition) will perform pretty well by today's standards.
Read: SBC Cylinder Head Assembly
The cylinder heads used on many 327 motors were 461 castings (#3782461) with 1.94" intake and 1.50" exhaust valves. These were the best flowing factory heads GM had to offer at the time. They are easily identified by the double-hump shape on the end of each head.
From 1964 through 1968, some, but not all, double-hump heads had 2.02" intake valves. These larger-valve heads were cast #3782461X and are known as "fuelie heads" since they came on 327/375-horsepower fuel-injected engines. These were also fitted to the 327/365-horsepower (Holley carb) Corvette engine.
350 Small-Block Chevy
An increase of piston stroke gave us the 350ci small-block in 1967. This is the most common size SBC. Other first-generation engine sizes are 302, 400, 307, 287, 262, and 305.
Read: Chevy Small Block History 1955-1969
Read: Chevy Small Block History 1970-1979
In 1968, the 327 Chevy small-block was updated with larger diameter crankshaft and connecting rod journals. The main-journal size increased from 2.30" to 2.45". The rod-journal size increased from a 2.00" diameter to a 2.10" diameter, and the connecting rods were now heavier and used 3/8" diameter cap-bolts versus the smaller journal 11/32" diameter.
Accessory Mounting Holes
Early Chevy small-block cylinder heads did not have accessory mounting holes on the ends of the head. Except for some early truck applications, it was not until 1969 that all small-block heads had factory-equipped accessory holes.
Read: Spray Paint Engine
The 350 LT-1 motor was the highest horsepower version of the Gen-One small-block Chevys. Power output was 370-horsepower in the Corvette, and 360-horsepower in the Camaro Z/28. The LT-1 featured a solid lifter cam, 11:1 compression, a 780cfm Holley four-barrel carburetor, and aluminum intake manifold.
Many builders will start with the specs of an LT1 small-block and then customize it to their liking.
2-Bolt vs 4-Bolt Block
Chevy 350 small-blocks were made with either 2-bolt or 4-bolt main bearing caps. The center-three main caps in the 4-bolt block had two additional bolts which were supported by the addition of heavier crankcase main-web bulkheads.
There was a tech article several years back where an engine builder tested a 2-bolt block to see how much power it would take before main cap flex. The horsepower level was near 600 before any main cap movement was detected.
If you're looking to build a healthy street motor, there's nothing wrong with a 2-bolt main block. But if your small-block Chevy build includes a high revving motor (over 6,000 rpm) and 500+ horsepower, and 4-bolt block is a good idea.
Was There A Factory 4-Bolt 327 ?
Neither 283 nor 327 Chevy blocks ever left the factory with four-bolt main caps, but they can be added. This is only required if you plan on making serious horsepower (500+) at very high revs (over 6,000 rpm). Before doing this, consider selling your vintage block to a restorer and building yourself a 350ci motor.
Switch From Carburetor To Fuel Injection
The first small-block Chevy to have fuel-injection was 1957, an additional cost option which gradually faded away in 1965. By the mid 1970's, SBC engines were being equipped with emissions and engine function controls, neither of which carburetors were ever designed to handle.
Since automotive emission standards were going to get even stricter in the 1980's, GM engineers began working on electronic fuel injection systems to replace the over-burdened carburetor.
The Chevy Crossfire engine offered in 1982-1984 Camaros and Corvettes was an important step in Small-Block Chevy history. Run by an electronic computer, a low-pressure high-volume electric fuel pump was mounted inside the gas tank, replacing the mechanical-style pump. In the 1984 Corvette, L83 engine horsepower was 205, with a peak torque rating of 290 lb/ft.
Tuned Port Injection
In 1985, Chevrolet introduced the tuned-port fuel-injected 5.7L small-block. With separate injectors for each cylinder, the new TPI system increased horsepower to 230. More importantly, torque increased to 330 lb/ft. A serpentine belt system replaced the multi V-belt set-up.
By the mid-eighties, fuel injection, coupled with on-board computers, helped the Gen One small-block achieve lower emissions, improved driveability, and better fuel economy.
Chevy and GMC trucks made the switch to fuel injection in 1987. The last of Chevy passenger cars with carbs were the 1988 Caprice and Monte Carlo.
One-Piece Rear Main Seal
In 1986, the two-piece rear main seal used from 1955 was replaced with a one-piece unit. Displacement of the block was now cast into the block next to the casting number.
SBC Camshaft Selection
In almost every small-block Chevy build, the camshaft is replaced along with the lifters. Selecting a cam usually involves a compromise between low-end and high-end power, but you don't need a wild camshaft to build a strong-running small-block engine.
Wade Owens of Cape Girardeau, Missouri, ran a 283ci motor in a 1966 Chevelle, and competed in NHRA's Stock Eliminator class. Duration on his cam was about 258/260 degrees at 0.050 inch, and lift for this engine combination is rules-limited to 0.399 inch, measured at the retainer.
With this relatively mild camshaft, Wade's Chevelle consistently ran in the mid-11s, which was at or under the national Stock Eliminator class record.
Read: Camshaft Selection Guide
SBC Camshaft Replacement
Replacing a cam with the motor in the car requires a few more steps than when sitting on an engine stand. As with all phases of engine assembly, care must be taken while installing a camshaft.
Read: SBC Camshaft Installation
Read: SBC Timing Chain, Gears, and Cover
On first generation small-block Chevy engines, lifters were either hydraulic flat-tappet or solid flat-tappet, with hydraulic roller and solid roller designs available in the aftermarket. The hydraulic flat-tappet lifter is the most commonly used, having quiet operation and requiring no adjustment once installed correctly. They work well in both stock and modified engines to about 6,500 rpm.
Mechanical (solid flat-tappet) lifters are generally used in applications where very high rpms (7,000 rpm or more) are needed. At idle, they will make a slight ticking sound, which is normal. They also need periodic adjustment.
Small-block Chevy valve-train assembly includes lifters, push rods, rocker arms, rocker nuts, and rocker balls. All Gen 1 small blocks use the same valve timing procedure, but there are several sizes of balancers and timing pointers.
Read: SBC Valve-Train Assembly
All Gen-1 SBC Chevys use the same firing order: 1-8-4-3-6-5-7-2.
During the production year of 1986, new aluminum heads brought a 40-pound weight savings and a five horsepower output improvement. Compression was slightly boosted from 9.0:1 to 9.5:1. These aluminum cylinder heads were first offered on the 1986 Corvette, and were the first to have the center-bolt valve covers.
Starting in 1987, small-block Chevy V8's were fitted with Vortec heads, which had better flow at lower lift than earlier heads. To improve intake gasket sealing, the mounting bolts were relocated to the valve cover center-line. This placed sealing pressure evenly on the cylinder head's mounting flange.
Can I Put Vortec Heads On An Early Small Block?
Vortec heads will fit earlier SBC blocks provided the correct intake manifold is used along with them. This is because the intake ports are taller than early small blocks.
"The world's best cam combined with a poor set of heads will produce an engine that's a dog. But bolt on a set of great heads even with a poor cam, and that engine will still make great power." - John Lingenfelter
Classic Car Engine Oil
The 10W-30 oil your car left the factory with is not the same 10W-30 that you buy today. There are more flat-tappet hydraulic cam failures than ever before, brought about by inferior foreign lifters as well as the removal of ZDDP additives from motor oils.
Read: Best Oil for Classic Cars
Lucas 10631 SAE 30 is a high-zinc break-in oil used for flat tappet camshaft break-in. No moly supplement or additional additives are needed with this oil. Not recommended for passenger cars with catalytic-equipped emissions controls.
Shop: High Zinc Break-In Oil
SBC Crate Engine
Although not seen in a new car since 2004, the Gen I Small Block is still in production by a GM subsidiary in Mexico. They are sold under GM's crate engine program and still very popular for replacement and racing/hot rodding.
NOTE: There have been many discrepancies found on crate engines. For any serious performance, it is wise to disassemble the motor and check all clearances.
Best Small-Block Chevy Book
I've read this book cover to cover at least a dozen times. Author David Vizard is far and away the best source for small-block Chevy building.