Main Caps
Gen I and II small-blocks have been offered with two- or four-bolt main caps. Most four-bolt main cap blocks have a two-bolt front cap and a two-bolt rear main cap. Now, before you run out and look for a four-bolt block or upgrade from two-bolt caps to four-bolt caps, keep in mind that a two-bolt block can withstand up to 500 hp, especially if you use quality main cap studs and nuts instead of the stock main cap bolts. The two-bolt bottom end has to be right, but it is often used in short-duration motors.
For stock street use and some performance and race use, a two-bolt block is more than adequate. If your power levels are going to be higher than this or if you are going to use large doses of nitrous, high-boost turbocharging, or supercharging, then go to a four-bolt block.
The Gen I and II main caps themselves are made of gray iron, nodular iron, or steel. Most factory-installed production blocks use two- or four-bolt gray-iron main caps, although some had nodular-iron caps (the nodular main caps have an “N” cast onto their surface). Most are straight caps, meaning the bolts enter the block surface at 90 degrees. However, some Bowtie four-bolt main steel caps are splayed, which means the two inner bolts enter the block at 90 degrees, while the two outside bolts enter the block at 70 degrees. They are splayed 20 degrees from perpendicular. The splayed caps provide more bottom end strength and perch in a place in the block that is subject to less distortion.
SB2: Short Name, Big Design Jump
In 1996, Chevrolet offered an all-new Gen I–based small-block racing engine called the SB2. It’s new-design block, aluminum cylinder heads, and two-piece, single, 4-barrel intake manifold made up the bulk of the changes. To make matters a little more confusing, Chevy introduced an SB2.2 engine design with further updates before being updated with the RO7 at least in NASCAR competition in 2007. Unless you’re really searching for something unique to run in your hot rod or high-revving weekend warrior, there’s not a big call for these engines any more. However, having something unique is what makes hot rodding fun, so let’s take a quick look at what made the SB2.
The cast-iron block (PN 24502600) is based on the proven Bowtie 1184 block design. The splayed four-bolt blocks feature revised lifter angles and lifter bore locations that work with the new SB2 heads. The lifter bores could be enlarged to 0.875 inch and the cam bearing bores were sized for big-block Chevy-style cam bearings.
The SB2 aluminum heads featured non-siamesed mirror port intakes and revised raised intake runner angles, which each point directly toward the intake manifold plenum and carb. Also, the locations of the intake and exhaust valves have been changed from the standard production sequence. The valve sequence on these SB2 heads is I, E, I, E, E, I, E, I. This valve sequence calls for a different camshaft, and aftermarket cam makers are set up to produce the cams and left- and right-bank pistons you need.
SB2 heads can be used on a stock production block or Bowtie block, but you need the updated camshafts and 0.180-inch offset roller lifters in order to maintain rocker arm geometry. The raised intake port runners along with the SB2 intake manifold runners have been repositioned so that there is a direct line from the intake manifold plenum to each cylinder. The intake port openings are almost 1/2-inch higher than those found on the 18-degree, high-port Bowtie race heads.
Extra-long-stem 2.15/1.65-inch-diameter valves (5.550 inches overall) are required. These are slightly longer than those used on the 18-degree, high-port Bowtie heads. The SB2 uses a 1.950-inch spring installed height. The intake valve angle is decreased to 12 degrees, and the exhaust is angled at 8 degrees, toward the bore centerline. On the CNC-prepared SB2 head (PN 24502560), the combustion chamber is shallow and measures 38 cc on the CNC-prepped head, which gets you 15.0:1 static compression with a flat-top piston and 358 ci. The chamber can be opened up farther to 53 cc to run a 9.0:1 compression ratio.
The SB2’s exhaust ports are raised and have a siamesed-port exit design with more coolant passages nearby to aid in cooling. The exhaust port openings feature revised exhaust header bolt patterns that are unique to the SB2 heads and require non-traditional tube header flange bolt holes to match.
Use head gasket PN 10185054 with these SB2 heads. The head calls for the standard head bolt pattern, but because of the revised port locations, some of the bolts pass through openings in the rocker arm valley and into the port runner floors. Screw-in AN plugs with O-rings are used to block off the head bolt access holes in the rocker valley.
The special, eight-bolt, cast-aluminum valve covers provide oil galleries and spray bars that can be added to shower the valve springs with pressurized oil. These help cool the valve springs to increase race durability.
The two-piece intake manifold uses a separate lower valley cover that provides for the coolant crossover, thermostat housing, and distributor mounting and keeps hot oil in the lifter valley off of the intake runners. The upper dry manifold runner spider and the single Holley 4-barrel carb with an open plenum are unique to the SB2 head intake ports and offer the advantages of easy removal of the upper manifold plenum and intake runners without having to remove the distributor or drain any coolant. ■
Keep these tips in mind: Whenever you replace the original main caps, you must have the new caps fitted to the block saddles in order to properly register the caps. The new caps must then be precision align-bored and align-honed in order to ensure that the crankshaft is properly centered in the block and that it is square with the front and back of the case and perpendicular to the cylinder barrels. Not all automotive machine shops are properly set up, or experienced enough, to do this kind of work. Make sure you patronize a shop that has the equipment and expertise to reliably align-bore and align-hone your engine.
When a block is align-bored, the distance from the crank center-line to the camshaft centerline may be altered. This alters the length of the timing chain needed on that block. Competition Cams, Cloyes, and other companies offer timing chain sets that have shorter chains to accommodate align-bored blocks. If you install a new standard-length timing chain and gear set on an align-bored block, there is so much slack in the new chain it looks like a used one out of a taxicab engine with 300,000 miles on the clock.
Places to Look for Small-Block Cores
Everybody knows that Chevrolet has been making small-block V-8s since 1955, but they also stopped putting them in production vehicles in the late 1990s as the Gen III took over. Finding rebuildable Chevy engine cores is not difficult; millions have been made. They have been used in passenger cars, station wagons, muscle cars, police and taxi vehicles, hot rods, boats, RVs, school buses, race cars, heavy-duty trucks, generators, and irrigation pumps. Some guys have even stuck them in airplanes.
Keep in mind that other GM divisions have used Chevrolet small-blocks to power some of their vehicles. Chevy 305 and 350 engines have been factory installed in Pontiac, Buick, Oldsmobile, and Cadillac cars. The 1977 to 1980 models are good places to look for carbureted Chevy small-block motors in BOP cars, and 1990 Cadillacs used a fuel-injected Chevrolet Gen I 350 with a roller cam and a one-piece seal. In 1991, Cadillac also used a 305 with fuel injection, hydraulic roller cam, and a one-piece rear main seal. Some Pontiac Firebirds in the 1990s have used Chevy LT1 Gen II motors.
Now don’t confuse these Chevrolet-made engines with the 350-ci motors that Pontiac, Oldsmobile, and Buick designed and used in their cars. What am I saying? Any Bowtie lover can spot a Chevy small-block in a junkyard or an arroyo from 2 miles away, no matter what’s wrapped around it. ■
It is a good idea to mark each main bearing cap (and rod cap) with a stamped-in number before you take an engine core apart. Each cap must go back into its respective position and the correct direction when it is reassembled. The factory puts an arrow on each cap to show the “front” direction. However, the caps are not numerically stamped. You need to stamp them before disassembly.
Main Bearings
Main bearings are generally available in the following sizes: standard (Std.), 0.001, 0.010, 0.020, 0.030, and 0.040 inch. When a crankshaft is checked for wear, it may be necessary to grind the crank journals undersize in order to restore the journals