A couple of decades ago, you could easily pick the boneyard for an inexpensive vintage engine core that would polish up nicely with a little cleaning and some machine work. Chrysler made millions of big-block wedges and LA-Series small-blocks, and by the 1980s, they were strewn on the ground like rocks. Those days are gone, and those “rocks” (at least the ones worth having) have turned into gold nuggets—with a price to match.
On the positive side, technology has marched forward, and the vintage V8 cores of the 1960s and ’70s have been replaced in those same scrapyards by 318- and 360ci Magnum small-blocks from the 1990s. These were used in everything from Ram trucks, to Dodge Dakotas and Durangos. Since they were based on the previous LA-Series of small-blocks, they easily fit between the fenders of our favorite vintage Mopar machines, making them the perfect candidate for a performance street build-up.
While you might frown that the Magnum isn’t the basis for a concourse-correct, numbers-matching mill, you’ll be happy to know that a good Magnum core can be had from most any local junkyard for well under $500. By “good,” we mean the block and rotating assembly is serviceable with a few basic clean-up and refurbishing operations. Moreover, because these Magnum engines were all electronic fuel injected, they don’t suffer from the debilitating bore wear and bearing abuse of their vintage carbureted counterparts. Modern engine management was designed to prolong engine life and reduce cold-start wear from fuel wash, not to mention counteract damaging detonation from low-octane fuel. This means these cores are more often than not in great condition, even with over 100,000 miles showing on the clock.
These engines first appeared in 1992 (5.2L only, the 5.9L in 1993), and were made by the millions through the 2003 model year. The 360ci (5.9L) Magnum had a rated output between 230 and 250 hp. Nevertheless, its role as a hard-working truck engine was underestimated by engineers and its thin-deck cylinder heads often had problems with cracking and warping—especially when run on low-octane fuel. This is actually a good thing for us, because not only did that prematurely inflate the supply of good short-blocks, it also brought good aftermarket cylinder heads into play to good effect.
One of those cylinder heads is the EngineQuest CH318A, a cast-iron replacement head designed ostensibly for the OE replacement/rebuilders market, but also conceived as a mild street performance part that with modest effort can be modified to produce significant gains in flow. It has a reinforced fire deck, a flow-cast intake port with improved port design and bowl area (verified at 237 cfm at .600-inch lift), and an as-cast, unassembled price of $660 per pair. The CH318A is compatible with the factory, fuel-injected intake manifold and any Magnum bolt-pattern intake, which is to say not very many intakes. To open up the use of LA-Series intake manifolds on Magnum engines, EngineQuest wisely offered the CH318B version, which has the LA-Series intake bolt pattern. This truly opens the door to big power numbers, and that’s exactly where we’re going with the Budget Sledgehammer Magnum!
In recent years, the Magnum small-block has become known as a latter-day performance engine in its own right; Mopar Performance even offers a read-to-go short-block assembly for around $4,600 (street price). If you’re strapped for time or lack the tools, this may be the way to go. But if you have the inclination and the time, you might try swinging your own garage build-up like the one performed here by IMM Engines of Indio, CA. Our Magnum 360 short-block costs less than half what the Mopar Performance crate engine costs, and even has beefcake forged pistons from Icon. By combining the stock block, crank, and rods with the forged Icon pistons, we’ll have enough strength to support over 500 hp. That’s safely over our 450hp goal and will provide the margin we need if we should decide to bolt on some nitrous or a small blower later on..
In our next installment of Budget Sledgehammer, we’ll be bolting on a set of IMM-prepped EngineQuest CH318B cylinder heads. IMM has adopted the EngineQuest head as their go-to piece for customers on a budget, and they have developed a program that improves performance substantially over the out-of-the-box flow. (For more on the IMM-prepped EQ heads click here [http://www.hotrod.com/articles/make-big-power-magnum-5-9l-mopar-heads/]). To the EQ heads, IMM will be adding Comp 1.6:1 roller rockers, an Edelbrock Performer RPM AirGap intake, a QFT Street-Q fuel mixer, and ignition components by Pertronix. We’ll put it on the dyno with some Patriot 1 ¾-inch long-tube A-Body headers and mufflers, then see if we can hit our 450hp goal on 91-octane pump gas. But first, let’s check in with IMM to see how best to bolt one of these short-blocks together!
Our budget Sledgehammer Magnum 360 short-block build-up was handled by Fred Hafliger or IMM Engines in Indio, CA. IMM builds all kinds of engines, but their specialty is high-performance Mopar. Here Fred readies the components for our short-block assembly.Before starting any engine project, the cylinder heads should be determined, as these fix many of the working parameters of the finished engine. Working backwards from these, the block, rotating assembly, camshaft, and induction will fall into place. These are budget-oriented EngineQuest CH318B Magnum heads designed for the use of standard LA-series intake manifolds. IMM machined them for larger intake valves, a larger throat diameter, and they were hand-blended in the bowl area. They cost $1,469 for the pair and flow around 266 cfm at .600-inch lift.Of course, you’ll need a satisfactory salvage core to begin with and we found a 5.9L Magnum from a late-model truck that was supplied by AAMidwest for $250. Compared to early-model LA-Series cores, late-model Magnums have far less bore wear and bearing damage due to the OE electronic fuel injection. This limits cold-start fuel wash and detonation, meaning a lower probability that the core will need serious machining.Since 318ci (5.2L) and 360ci (5.9L) cores look almost identical, you’ll want to look for the casting number in the block. This 5.9L core is cast with the numbers “360” in the side.Before beginning any engine build, you’ll want to clean and inspect the block. Since salvage cores are plentiful and cheap, Magnum cores with cracks or severe wear should be discarded. At this point, our 5.9L block has been cleaned, inspected, and magged.A check of the bores revealed they were well preserved. Our 4-inch bore was brought back to life with a clean-up from a ball-brush hone. Only once the bore is established and the main and crankshaft journals are checked should rings, pistons, and bearings be ordered. For an engine of our expected power level, it is not necessary to perform more costly operations like deck equalization, torque-plate honing, or hot honing.We did have IMM install a new set of cam bearings ($65) before stabbing in our Comp Thumpr hydraulic-roller camshaft. (IMM reused the factory thrust plate and fasteners.) With the 1.6:1 ratio roller rockers we’ll be using, the cam specs out to .556 inches of lift on the intake and .542 inches on the exhaust side. Duration (at .050-inch lift) is 235 degrees on the intake and 249 degrees on the exhaust, ground on a 107-degree lobe separation angle.Our late-model Magnum core took fresh main bearings in the standard size (King MB5534SI, $43 from Summit). Even with a core in good condition, the bearings should always be replaced.Here, the main bearing caps receive fresh King bearings. Note how the main caps are numbered, and that the center cap is the home of the thrust bearing, identified here by how the bearing wraps around the side of the cap.You’ll need a short-block gasket set (FelPro CS98982, $58 from Summit) which contains new front and rear main seals, oil pan gasket, water pump gaskets, and fuel pump gasket. Here, the rear main seal is getting a dab of RTV silicone to hold it in place. Care should be taken not to get any on the seal lip or else leaking will occur.Before the crank goes in, a good assembly lube should be used to coat all the bearing surfaces.Since our power level will always be well below 600 hp, we decided to re-use our factory cast-iron crankshaft. Before dropping in the crank, polish and clean all the bearing surfaces. Once in place, the crank should glide easily without binding.We also reused the factory main caps and bolts; they are fine for this power level and saved us some money. The bolts were cleaned and lubed with 30-weight oil, then torque to 85 lb-ft.A critical operation you’ll want to perform is checking the crankshaft endplay once the main caps are torqued down. You want to see between .004 and .008 inches of play. Ours specced out at .004 inches.A new double-roller timing set is cheap, and good insurance for a stable valvetrain. This Mopar Performance timing set (P5249267, $69 from Summit) was bolted on with a mechanical fuel-pump eccentric on it. We’ll be dropping a QFT double-pumper on top and hoisting it between the fenders of a ’73 Duster, so a mechanical fuel pump is what we want.Before we began, we found ourselves at a crossroads: do we save money and stick with the stock cast pistons—limiting our compression, valve diameter, and valve lift—or do we step up to forged slugs? This forged piston from Icon (IC741-STD) would bump our compression ratio to 10.4:1 (from 9.1:1), giving extra room for our 2.02-inch intake valves and allowing a higher-lift cam. Being the same weight as stock, they don’t require the rotating assembly to be balanced either, saving us a bit more cash. At just $627 a set, the Icon pistons were a no-brainer.IMM cleaned up our stock forged rods and press-fit the pins on with this tool. You’ll want a real machine shop to do this for you; IMM charges $55 for this operation (set of eight).The Icon pistons come with a Keith Black ring set (1/16, 1/16, 3/16) which includes file-fit ductile iron top and plasma moly second rings. For our naturally aspirated 4-inch bore street motor, we want about 16 thousandths gap on the top ring and 20 thousandths on the second ring.IMM like to place the top ring gap under the intake valve relief and the second ring gap at the exhaust valve relief, making them roughly 180 degrees apart.Before installing the pistons in the block, press in the new rod bearings (King CR805SI, $22 from Summit) and smear a dab of assembly lube on them.This handy ring compressor is used to guide the rings into the bores; a piston knocker is used to deftly urge the assembly into place. Beforehand, you should apply a thin film of 30-weight oil to the cylinder bores. Note that it’s critical to observe both the rod cheek and intake valve orientation along the engine’s north/south axis (chamfers along crank throws, reliefs matched to valves).Once again, the factory rod bolts were cleaned and reused. After inserting new rod cap bearing shells, the bearings were lubed and the caps attached with a speed wrench. A film of 30-weight oil should be applied to the bolt threads and the underside of the bolt head before torquing to 50 lb-ft.While you might be inclined to believe all cam and timing gear manufacturers are perfect, mistakes do get made in manufacturing. Don’t just line up the timing gear dots and let it eat; the time you don’t verify the valve timing with the cam card is the time you’ll invite mechanical carnage.We won’t go into detail on how to set-up and check camshaft timing here, but we will show you that the math worked out just as advertised with the cam checking in with 107-degrees of lobe separation angle.We’ll be reusing the oil pick-up from the salvage core, but replacing the oil pump with a high-volume Melling pump (M72HV, $70 from Summit). This pump will deliver 20 to 25 percent more volume than stock. IMM likes to increase the pressure threshold of the pump by adding a shim (actually a washer) between the spring and the plug.The oil pump, pick-up, and oil pan (center-sump Summit SUM-G3536, $50) have been bolted on and a new timing cover (Dorman 635-401, $179 Summit) added. A coat of Hemi orange paint went on before a new PowerBond damper was bolted up (PB1108-N, $94). The final operation of our short-block assembly was to verify the alignment of the timing mark on the damper (shown)
