Installing the four-bolt caps begins with bolting them in and torquing them to spec at the original inner holes. Be sure the mating surfaces are perfectly clean, and install the caps with the bearing locating tang at the same side as on the block. Use extra care to ensure the center thrust bearing cap is centered fore and aft on the block saddle. The stock caps fit inside the stepped-down area of the main saddles, while the Milodon caps extend outward for the angled outer bolts in the web area going to the pan rail.
Street-stroker Mopar A-engines are a recent development, but how well they work depends upon the rest of the setup. In mild form, they're great low-end torque makers. In the Nov. '01 issue of Mopar Muscle, we did some porting mods on a set of W-2 heads and found serious airflow, so a plan was formulated to build an all-out combination to let them breathe in the real world.
Building a stock or mildly modified engine is easy. Just clean everything up, lay out the replacement parts, break out the wrenches, and put it together. However, the more you deviate from the factory plan, the more involved the buildup gets. Before we assembled our engine using one of Mopar Performance's stroker cranks, we selected a 360 block as a base. We located and bought a premium early casting from a junked '72 commercial van, which turned out to be a virgin core with little wear-the perfect foundation for a big-inch buildup. We already assumed that some custom block work would be required.
Beyond the basic stroker clearancing, we went with several mods to the block looking for greater durability, including a set of four-bolt mains. Other changes were required to work with our choice of performance components. The actual building can't start until the grinders, drills, and taps are put away, so we mocked-up where we had to fit it together and went to work. We will cover the block prep this month and begin our buildup story in the next issue of Mopar Muscle.
The bore-and-hone job is critical to performance, with accuracy in indexing the bore location, clearance, roundness, straightness, and surface finish, all adding up to power production. JGM uses a torque plate while honing the bores whenever possible to simulate the bore distortion caused when the cylinder head is bolted into place.
Four-Bolt Bottom End
Though successful and durable, Mopar small-blocks are regularly built with the standard two-bolt main caps. For our stroker, we wanted an extra measure of durability. To accommodate the increased loads, which are inevitable with the long crank stroke and high rpm, our '72 360 block's bottom end was beefed up by the installation of a set of Milodon four-bolt main caps. The Milodon caps are high-strength 110,000-psi nodular iron, which Milodon claims is easier on bearings than steel caps and maintains better operating alignment since they have the same thermal expansion rate as the block. The caps were fairly easy to install, a job we handled ourselves with the use of the cap grinder at Specialized Motor Service. To finish the install, the mains will need align boring, which should be performed by an expert machinist.
Meticulous Machining
A performance engine buildup is only as good as the quality of the machining and the quality of the machining is only as good as the man behind the machine. Once the main caps were installed, we took our stroker block to Jim Grubbs Motorsports (JGM) in Valencia, California, for the critical, final cylinder bore and deck finish.
Lifter Logistics
Since we planned to use a solid roller cam in our big small-block, traditionally this means blocking the oil to the lifter bores. Our roller cam and components are from Crane. They claim their No. 69542-16 roller lifters will work in small-block Mopars without bushing the lifter bores or sleeving the oil galleries to block or restrict the oil flow. Normally, this is a problem; we plan to install them and see for ourselves. Getting the lifters into the block still required some minor mods to the lifter valley to clear the link bars, another simple do-it-yourself mod.
Crankcase Clearance
With a crank throw of 3.58 inches, the 360 was Mopar's longest-stroke small-block. To stuff in a 4.000-inch arm, you need to make some room. While some other types of engines require radical reworking for a stroker arm, the LA-block Mopar with its 9.599-inch deck height will swallow a 4-inch crank with minimal effort. The clearancing is simple enough to do by hand at home with a die grinder and carbide cutter.
The first step is to drill into the main galleries to tap in for the crossover tube. We wanted to ensure free flow between the two, so they were drilled to 7/16 inch to take a 1/4-inch pipe thread. The location is just to the outside of the rocker feed passages. The hole should be at a slight angle toward the oil flow. At first, we drilled undersized to properly locate the hole.
Oiling Alterations
The stock Mopar small-block's oiling system is much better than most, but for extreme duty, some modifications have been developed. We've run the stock system reliably to the 7,000-rpm mark without any failures. That said, we wanted this stroker to have the capability to go high rpm, which becomes more stressful with the long arm. Is it really necessary? There's no way to quantify it unless the engine is built without mods, fails, is modified, then lives. We've heard of main bearing failures at high rpm in racing applications. Our plan was to alter the system circuit using an old-and-proven change designed to increase the high-rpm oil availability to the mains.
The stock system feeds the No. 4-No. 1 main bearings from the right (passenger side) oil galley via four passages drilled down from the galley to the main saddles (the rear No. 5 main has a separate oil supply gallery). From the front main, the oil goes back up another drilled passage to supply the left galley. This mod taps oil from the right gallery and connects it to feed the left with a transfer tube. The original No. 1 main feed from the right gallery is blocked and the oil now travels via the crossover tube to supply the left gallery and down what was the left side's supply passage in reverse to supply the front main. It's a lot simpler than it sounds and reduces the oil demand and velocity in the right gallery since it now only needs to supply the center mains.
Gearing Up
To drive the camshaft with the ultimate in accuracy and bulletproof durability, we wanted to run a Milodon geardrive. These drives are real race-fixed idler systems, not to be confused with floating dual idler noisemakers. The Mopar small-block version fits under the stock timing cover. The fixed single-idler geardrives run at a precise preset clearance between the gears, which needs to be set up during installation.
