Cam phasing is also critical to this effort, so when test-assembling the engine, the cam should be accurately degreed to ensure proper clearance between the cam lobes and the rods. ![]() Big-lift roller cams often present the biggest clearance problems with a 383, so this is something that should certainly be checked when trial-fitting your next 383. Since maximum lobe height on any cam cannot be larger than the diameter of the cam journals, one way to gain lift with a cam is with a smaller base circle. The base circle is the starting point for any lobe lift. Small-base-circle cams are another suggestion when building a 383 stroker motor. One way to help with this clearance to use a new rod bolt from ARP (PN 134-6027, $65.88, ), which offers additional bolt head clearance for the camshaft. Using stock 5.7-inch rods in a 383 requires grinding the leading edge of the rod near the bolt on rods 1, 2, 5, and 6. Because of the additional stroke, the upper portion of the big end of the connecting rod swings very close to the camshaft. There's a second and equally important internal clearance issue on 383s between the camshaft and the connecting rods. The pan rail may not always need to be clearanced. The extent of the grinding will depend on the rod design and position of the rod bolts. Most blocks will require clearancing at the base of each cylinder, and many will also need a slight amount of grinding just on the inside edge of the pan rail. ![]() The key is to remove as little iron as possible because there is a water jacket directly beneath the area you will be grinding. The rod bolt nuts (or bolt heads for capscrew rods) will probably either hit the block or come extremely close, requiring clearancing with a die grinder and a carbide cutter designed for cast iron. If you are building a 383 for the first time, mock up the crank and rods with dummy pistons so the rods swing in their proper orientation. The first area for attention is where the rods swing by the base of the block just inboard of the oil-pan rail. Internal ClearancingStuffing a 3.75-inch stroke crank into a block designed for a 1/4-inch-shorter arm requires minor trimming. SRP makes a very short piston for this specific application, although the pin most definitely intrudes into the oil ring land. For example, a small-block Chevy with a 4.00-inch stroke and a 6.00-inch rod will require a very short 1.00-inch compression height to squeeze it all into a standard-deck-height small-block. Many engine builders will limit minimum compression height to 1.00 inch. While there are many custom pistons with the wristpin in the ring pack, there are limitations to the minimum piston compression height. At some point, adding a longer rod will push the wristpin too far into the ring package, which reduces piston stability at higher engine speeds. As the length of the connecting rod increases, the piston's compression height shortens and the wristpin moves closer to the ring package. This allows up to 0.025 inch of room to mill the deck to create a zero deck height between the top of the piston and the deck of the block. For example, a typical 383 piston intended for a 5.7-inch-long connecting rod will have a compression height of 1.425 inches to create that same 9.00 deck height. Of course, this requires a custom piston with a shorter compression height. ![]() This led to the better idea of combining the longer 5.70-inch 350 rod with the 3.75-inch stroke crank, which made the rod angularity much gentler on the cylinder wall. Compression height is the measurement from the wristpin centerline to the flat portion of the piston. To define everything, the deck height is the distance from the crank centerline to the head surface of the block. The formula is simple: Half the stroke, plus rod length, plus piston compression height needs to fit within the block deck height. Let's add up the numbers to see how this works. The difference is 0.135 inch, which just happens to be exactly half of the added stroke at 0.270 inch. All stock small-block Chevy connecting rods measure 5.70 inches, except for the 400, which measures 5.565 inches. Instead of moving the piston's wristpin location upward, they shortened the connecting rod. Bumping the stroke required changing a few other details as well. When the time came to design the 400, Chevy engineers had to stuff a 3.75-inch stroke into the 265's same block architecture. The original 265ci small-block used a 3.75-inch bore and a 3.00-inch stroke. In the case of the stroker small-block Chevy, it comes down to squeezing a bigger arm into a standard small-block. Stroke, connecting-rod length, and block deck height are the variables the engine designer must play with when creating a new engine. Stroke Stuffing All production small-block Chevys share the same deck height of 9.025 inches.
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