1972 Chevy Pickup Small Block Engine - Low-Budget Building BlocksPosted in Features on February 1, 2001 Comment (0)
In the realm of modified V-8 engines, none are more popular than Chevy's small-block. The funny thing is that all of them will be built differently. There are probably more recipes on how to build a small-block Chevy than there are for an apple pie. But if you talk to truck owners who have built one themselves, they often tell you that their engines turned out to be too expensive and end up with either too much power that they really can't use or not enough bottom-end torque to get the truck moving.
How do you build the right engine for a specific 'wheeler? The answer will depend on the components used and how well they match the needs of the application. For example, a 350 small-block in a '72 Chevy pickup that makes 450 hp and 300 lb-ft of torque will be less usable off road than if it were equipped with the same size engine making 300 hp and 450 lb-ft of torque. How is this possible? It depends on where and when the power is made. Heavier vehicles, such as pickup trucks, need a very broad horsepower curve. This means that power needs to be made from idle to as far up the rpm range as possible. On a lightweight vehicle, we can build an engine that will sacrifice some of the bottom-end power and use it to gain added speed at higher rpm.
Although all of the engine's components make a difference in producing horsepower, the camshaft, the cylinder heads, the intake, and the exhaust system are key factors in placing the power at a particular rpm level. This is where many enthusiasts make their mistakes. Novice engine builders will often purchase components that are not meant to work with each other or components that are intended for high-rpm racing use. The end result is an engine that doesn't match the application. This is also true with some crate engines, where peak horsepower ratings are often the only information that enthusiasts consider before making a purchase.
Matching the correct cylinder head, camshaft, intake, and exhaust systems will ultimately optimize the flow of air and fuel into and out of the engine. The design, in combination, will make dramatic increases in horsepower and torque. For example, smaller cylinder port configurations mixed in with moderate lift camshafts and dual-plane intake manifolds will create torque. Larger ports in a cylinder head combined with a high-lift, long-duration camshaft will make more top-end horsepower. What will work best in your particular application will depend on what kind of vehicle you are building. If you are looking for something to pull a trailer, you will want a lot of bottom-end torque. If you are building a high-performance on- and off-road truck that may see some moderate-speed prerunner action, you might want an engine with more horsepower. For the majority of truck enthusiasts, the optimum street/performance engine is somewhere in between. This means having an engine that will produce good torque at low rpm, while being able to pull strong at higher rpm levels.
A simple experiment will show how two combinations of components will dramatically alter the power curve of a Chevy 350 small-block - with a low budget and using available parts combinations. The first stage of the test would be to perform a simple, low-budget rebuild, suitable for a mild-performance off-road truck. However, we wanted all of the machining done to the highest quality. This process involves squaring all of the block and head surfaces and using a dial indicator to check the results. Our rebuild also incorporated as many of the original parts as possible, which increased the torque potential of this engine on a minimal budget. This meant using the existing heads, connecting rods, and crankshaft.
We selected Federal Mogul's Sealed Power 328hp rebuild kit (PN HPK102), which included everything necessary to completely rebuild a 350 small-block. The rebuild kit also contains many upgraded components. This included a new Sealed Power hydraulic camshaft (PN KC1013R) that features 0.443/0.465 inches of lift and 214/224 degrees of duration at 0.050 inch of lift. This camshaft profile characteristically improves low-end torque while still providing increased horsepower. This cam also creates more vacuum to draw in the air/fuel mixture. The kit includes a set of (PN H100CP) hypereutectic pistons that have graphite-impregnated skirts that reduce cylinder wear. Combined with OEM heads, this combination will dramatically increase the torque and horsepower curve of a typical 350 and give our engine an overall compression ratio of 9.73:1.
We started off using an old Corvette engine that had been sitting for years in the back of the garage. It was removed from the Corvette because of a knocking sound, which resulted from using an old vibration damper that came apart after some quarter-mile runs. There's a lesson to be learned here. From our initial inspection, everything on the engine looked OK, and it was chosen for our experiment because it was equipped with four-bolt mains and had a good set of factory heads on it; the real reason was that it didn't cost us anything. There was another lesson to be learned here as we soon found out.
We put the engine in the back of our pickup and took it over to Dave Akard of Burbank Speed and Machine. Arrangements had already been made with Dave to build the engine to our specifications and to have it tested on the shop's in-house dyno. Burbank Speed and Machine is known for building many high-powered racing engines for dirt track and other applications.
The first step in any rebuild is to completely disassemble and clean the block. Once all of the original components passed the magnafluxing test, it was time to gather up parts for the assembly. At this point, we came across our first problem. The crankshaft had been severely scoured from the bad harmonic balancer, and we needed a new crank. Although we could have found a replacement cast crank for about $150, we opted for a high-quality forged-steel replacement crank from Federal Mogul for $400. The forged-steel crank will be able to handle any future horsepower.
The second problem was that the Corvette engine was already bored 0.060 over and couldn't be bored any larger without some reliability problems. Dave suggested we search for a new four-bolt main block. We scoured several junkyards for a suitable block to work with. Not trusting what we had found, we discovered an abundant source of guaranteed cores at RPM Engines in Wilmington, California.
RPM also rebuilds and sells factory replacement short-blocks and long-blocks and complete engines for both Chevy and Ford applications. The company offers a three-year/36,000-mile warranty on more than 5,000 engines carried in stock and guarantees its cores to be rebuildable. We opted for a bare-block core that had four-bolt mains and could be bored without any problems. The core had a price tag of $75. A complete core from RPM that includes pistons, rods, a crank, and heads normally runs about $200.
Our new core was then cleaned, line-bored, checked, and readied for machining. Dave bored the block to 0.040 over and honed the cylinder walls. Our factory connecting rods were resized, honed, and fitted onto the Sealed Power pistons. Our original heads checked out OK and were resurfaced and squared. We used a new set of valves, which were the same size as factory, using Sealed Power 1.94 intake and 1.5 exhaust stainless steel valves. We also decided to upgrade the heads by removing the pressed-in rocker arm studs and replacing them with the Sealed Power screw-in studs. Since we wanted to create some torque out of this engine, we also decided to stay with the factory cast-iron intake manifold and retain the Quadrajet four-barrel carburetor.
Now that our long-block is rebuilt, the next stage is to install the induction system and test it on the dyno. Equipped with the factory heads and the Sealed Power components, we should expect to see a little more than 300 hp at 5,000 rpm with the same torque readings around 4,200 rpm. Our next issue will cover the installation of a set of roller tip 1.6 ratio rocker arms. This should slightly improve horsepower readings across the rpm band. Furthermore, we will be bolting on Holley's System Max cylinder heads, a camshaft, and an intake system to see if these alone will boost our engine's horsepower to more than 400 hp. The dyno will tell the tale.
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