Starting with a production...
Starting with a production Chrysler 360 LA-Series small-block, the bottom end was filled with basic parts that are more than up for performance use. An Eagle stock-stroke crank is spun by stock-length Scat I-beam rods, with KB Icon forged pistons providing the shove. The block received a partial fill in the water jackets to better support the cylinder walls.
Maximizing bang for the buck comes down to making the most of a given combination of parts. When it’s done right, the engine will throw down power numbers that belie its modest parts list, packing a heavyweight punch in an unassuming package. This small-block Mopar from SKMFX Engines is a testament to that ideal, with righteous output from commonplace parts. This engine was built for competition in the Street Division of our annual engine building competition, the AMSOIL Engine Masters Challenge. Jesse Robinson and his teammates from SKMFX Engines assembled this bullet as a backup engine to compete in place of their big-block, which was held up by part delivery delays. The stout output from this very basic production-based combination was impressive.
SKMFX started with an ordinary production “LA-Series” Mopar 360 block, and proceeded with a bottom end build that would be typical of any budget street effort. The block received basic prep, including a .060-inch overbore, line honing, and decking. Robinson also added a short fill to the water jackets: “I’m a big believer in the short fill, and I like what it does to the water and oil temperatures. The exposed cylinder ends up at about 4 inches, and it stiffens the cylinder walls considerably,” Robinson says. The block also had the main oil feeds enlarged to 9⁄32 inch, but was otherwise stock in terms of the lubrication system.
The stock production main...
The stock production main bearing caps were retained, though high-strength ARP main studs provide extra clamping. Jesse Robinson from SKMFX tells us the factory 3.58-inch stroke is far easier on the bottom end assembly than a long-armed stroker.
Filling the block is a rotating assembly based on the stock 360’s 3.58-inch stroke. Rather than using the stock cast-iron crank, Robinson selected an Eagle 4340 steel crank. “This crankshaft is a good value for the price at under $600,” he says. “One of the major hiccups with the 360 is the external balance. A few years ago, I had a stock 360 crank internally balanced and it cost as much as this Eagle crank because it took six slugs of Mallory metal to balance it. At that point it makes sense to move to the steel.” The rods are a set of Scat I-beams in the stock 6.123-inch length. Robinson explains this choice: “I don’t like the H-beams for many applications; they are just too heavy. These Scat I-beams are just a beautiful set of connecting rods, and a great value for the money.” Filling the cylinders is a set of KB Icon pistons and Perfect Circle rings. The internal parts combination seemed to follow the theme of budget-oriented replacement parts that are proven durable in a high-output application.
The KB icon pistons are wrapped...
The KB icon pistons are wrapped with a conventional Perfect Circle 1⁄16-1⁄16-3⁄16 ring pack. The most exotic part of the ring package is the Napier-faced second ring, which aids in oil control. Bearings are coated Clevite pieces.
Topping It For Power
A similar approach followed up to the top of the engine with the EngineQuest Iron Magnum 318B cylinder heads. These heads are designed as production replacement units for the OEM Mopar Magnum heads, but are revised with the earlier “LA-Series” intake manifold bolt angle. The castings are significantly improved compared to the factory units with both durability and performance in mind. Robinson’s experience with the EngineQuest cylinder heads has been overwhelmingly positive: “I started using EQ heads on Chevrolets, using their Vortec heads on 350 and 383 Chevys, and the results were never disappointing. I started to experiment with the Dodge heads, and again they produce very good power.”
Robinson modified a stock...
Robinson modified a stock windage tray by opening large drain backs, and then bonding screens in place with epoxy. Many small-block Mopar fans question the validity of a windage tray, however, Robinson related that he has seen substantial power gains with a tray in place.
Oiling was handled by a Melling...
Oiling was handled by a Melling pump, with the pick-up relocated to the rotor cover. Robinson explains the move was primarily to ease making the custom oil pickup. The lubrication system is essentially stock, with the exception of opening up the oil passages to the mains.
A custom COMP hydraulic roller...
A custom COMP hydraulic roller cam works the valves, with more aggressive timing and lobes on the intake side. Cam specs were ground to 246/244-degree duration at .050, with .646-inch lift. A tight lobe separation angle of 106 degrees promotes torque.
A secondhand set of T&D rockers...
A secondhand set of T&D rockers were mocked-up on the EQ heads, and the geometry was optimized with custom 5.250-inch length valves measuring 2.08 inches in diameter. This arrangement bolts to the stock Magnum-style pedestals, though the fasteners are upgraded to ⅜-inch diameter rather than the OEM 5⁄16-inch dimension.
Providing for pushrod clearance...
Providing for pushrod clearance required substantial clearancing of the valve cover rails at the intake side of the head. The pushrods are Trend units, which Robinson praises for their minimal deflection.
Due to clearance issues with...
Due to clearance issues with the rockers and pushrods, standard small-block Mopar valve covers could not be used. These fabricated aluminum covers were sourced from an eBay vendor, and feature an internal rail design for increased clearance.