Build a 1,200 HP 392ci Hemi Short-Block for Under $3,500

2022-04-26 07:51:52 By : Mr. Louis He

Hot rodders are at a crossroads of sorts. New performance machinery from the factory is not only getting a lot more powerful, it's getting mighty expensive too. Folks with well-endowed wallets are gobbling up Detroit's latest 500-, 600-, 700-, and 800-horsepower machines with gusto, leaving the regular-guy DIY hot-rodder on the side of the road playing catch-up. And it's only going to get worse as the inevitable flood of uber-powerful EVs hits the road en masse . For those with gasoline in their veins, like it or not, the bar for what's considered fast is now a lot higher. Mopar fans, however, are fortunate to have in their corner the third-generation Hemi , a powerplant that's been in production for 20 years now.

Stellantis ' predecessor, Chrysler, put plenty of latent capability in its third-gen Hemi V-8 architecture, and these engines are ubiquitous in salvage yards across the country. The largest variant, the 392ci Hemi, is made in two basic versions: passenger-car ("Apache") and truck ("BGE," or big gas engine). The parts are largely the same, but the BGE truck version of the 392 (2014-present) is not only more prevalent (and thus less expensive as a used core), but also incrementally better in some critical areas like the cylinder heads and block. If you're a Mopar fan on a thin dime, and you want to leapfrog over the sea of bellybutton Hellcat Hemis , Camaro ZL1 s, Shelby Mustang s, and Corvette ZR1 s (not to mention the onslaught of 800-hp EVs in the wings), a junkyard 392 Hemi is what you're gonna want.

Related: Junkyard 392, Part 1—Scoring a $400 Junkyard 392ci Hemi From a Ram Truck

We discovered our junkyard 392 Hemi in a local wrecking yard for just $400; we know little about the 2016 Ram 2500HD it came from other than the fact that the engine wouldn't run before it was taken out. It's a better-than-average deal, and when we spoke with a representative of EngineQuest Cores & Recycling we discovered that BGE 392 V-8 engine cores typically sell for $1,000-$1,500—still a relative bargain compared with a salvaged Hellcat Hemi and associated kit for around $20K. In Part one of our Junkyard 392, we covered the disassembly and post-mortem of our $400 392 BGE core and found it to be A-OK. We wrestled for a while with what to do with it; do we take the cheapest road possible and pound on it until it blows up, or do we make it indestructible so that we can test a bunch of your favorite parts like headers, cams, intakes, and various power adders? We settled somewhere in the middle so that we could keep things screwed together under pressure without breaking the bank.

The goal here is to build the BGE 392 Hemi short-block to handle 1,200 hp safely and reliably, leaving enough cash in the bag to fortify our stock BGE 392 cylinder heads, induction, and valvetrain. We want to come in at a price tag decisively under $20K while pounding out a solid 1,000 hp, but you'll likely be able to do it for less if you don't punish your 392 with hundreds of dyno pulls for product testing like we plan on doing. One issue that crops up here is that no self-respecting engine builder like IMM Engines of Indio, California, is going build an engine full of cost-saving shortcuts—that's a staple of reality TV and social media that's designed to create a spectacular on-camera failure, not usable test data. Our plan with this build in partnership with IMM is to be cost-conscious where we can, but smart where we need to be. IMM's Brian Hafliger made sure we didn't skimp in the wrong areas and we'd recommend him for building any kind of Mopar V-8.

With our BGE 392 Hemi core checking out good with IMM, we got in touch with the third-gen Hemi experts at Modern Muscle Xtreme (MMX). Inspection revealed we'd need an overbore, and after consultation with MMX's head engine-builder, Byron Walker, we selected a drop-in piston/rod upgrade that would work with our stock forged 392 crankshaft and BGE 392 block. Comprised of full-floating 2618 forged pistons from Mahle and forged H-beam rods from Molnar Technologies , our MMX drop-in, no-balance power package combo specced-out at a 9.7:1 compression ratio. Ideally, customers will want to optimize the compression ratio for either a naturally aspirated configuration (between 10.5:1 and 11:1) or a power-adder scenario (around 9:1), but we wanted to be able to use this 392 for either configuration, so we split the difference for future product testing under both regimes.

MMX's drop-in, no-balance piston/rod combo (at right) in theory can be installed directly without balancing, and the crankshaft doesn't even have to come out. (The bobweight of the MMX combo was right on point when we checked it). Since our 392 Hemi core was damaged by cylinder wall rust, however, dropping it straight in wasn't an option. The third-gen 392ci Hemi has a factory bore of 4.09 inches versus the 3.92-inch bore of the 5.7-liter Hemi, but a 0.010-overbore put us at 4.100 (393 ci). The factory 392ci BGE Hemi piston (left) has a 10:1 compression ratio; it's a hypereutectic casting on a full-floating pin attached to a powdered-metal connecting rod. Pistons in the passenger-car Apache 392 (not shown) have a higher 10.9:1 compression ratio, but otherwise the pistons and rods have the same construction as the BGE 392 Hemi. Both the factory Apache and BGE 392 Hemi piston/rod combos are done at around the 650-hp mark—not enough for what we'll need. 

The left-side arrow shows how much taller the ring land is on the Mahle PowerPak piston compared to the OE piston. This pulls the ring back from the piston crown, shielding it considerably from the high heat to be expected from boost and nitrous. The 2816 alloy also has over twice the strength of the stock cast piece, which is super critical as the temperature and pressure increases. The priority of the OE design (besides cost) is to limit the range of thermal expansion for reducing emissions, and the hypereutectic alloy and smaller crevice volume (right arrow) of the factory design helps with that.

Before we dig into the specifics of our 392 Hemi build with IMM Engines, we wanted to point out that you can follow along at home and build one yourself—if you have the proper tools. We're pricing the cost of the Junkyard 392 as a DIY proposition, and some of the tools IMM uses may be overkill for the home-garage-based builder. To help you through the process, we'll be pointing you towards the specialized tools you may not have in your man-cave or she-shed, and Summit Racing has a fantastic selection of affordable engine-assembly tools designed for both hobbyists and pros.

One area we recommend you may want to leave to a professional, however, is the block machine work. As a budget-oriented build, we kept things simple by doing just a simple cylinder hone with a .010-inch overbore. To prevent any money being wasted, we had IMM hot-tank the block and inspect it for hairline cracks. For a more serious race effort, you may want to add torque-plate honing or even hot honing to the list. Depending on whether there's any additional concerns with your core, your machine shop may recommend other operations like deck equalization, align honing/boring, O-ringing, new cam bearings, lifter bushings, or a partial hard-block fill. If you're comfortable with tackling a simple cylinder hone job at home, Summit offers a drill-powered cylinder hone tool from Lisle here for $173.99. In most cases, your thorough inspection at home will leave you with a core that needs nothing more than a cleaning and a modest DIY clean-up hone for stock-sized rings and pistons.

One important check you'll want to make before spending lots of time on assembly is to verify the flatness of the deck. The sealing integrity of the Hemi's multi-layer steel (MLS) head gaskets depends on making the deck as flat as possible and you'll need a machinist's straightedge designed for precision measurement like this. (We found an excellent machinist's straightedge on the Summit website here for $35.99). Check the deck's flatness across multiple points using a feeler gauge (like this Lisle unit from Summit, $8.99). IMM's Brian Hafliger is using a .002-inch feeler gauge in the photo as a go/no-go test. If it passes under the straightedge, you'll need to have your machinist deck-equalize the block. 

Before you begin screwing together your Hemi short-block there are a couple of preparatory steps you'll need to complete, one of them being file fitting the rings to the cylinder bores. You'll need a precision feeler gauge, a ring-squaring tool, and a ring filer. Summit's big-boy-pants-sized ring squaring tool costs $51.99 (you can use the old piston with its top ring installed if you want) and Summit's pro-style ring filer comes in at $649.99. Our Mahle 4105MS112 rings (included with Mahle's PowerPak pistons) are a .010-over (4.100-inch) 1mm/1mm/2mm low-drag, standard-tension set that we're giving a boost-friendly 0.026-inch gap (top and second ring). If we were building the 392 Hemi for naturally aspirated use, we'd tighten that up to 0.020-inch for the top ring and 0.021 for the second ring. With ring gap on a boosted or nitrous engine, it's important to remember that with more boost comes more heat, and with more heat comes more ring expansion. When the ring ends touch from being too tight, they become micro-welded. This results in lifting the ring land, and that spells the end of that piston.

In preparation for installing the crank, verify the bearing clearance, which needs to be 0.002-inch. Start by checking the inside diameter of the main journal with the bearing shells installed and the cap torqued to spec. (We are using ARP's 244-5400 Hemi main stud kit, considered mandatory at this power level). You'll need a set of precision inside micrometers (like these sold by Summit for $25.99) as well as a set of outside micrometers for the crankshaft journals (Summit sells them here for $59.99). When you subtract the outside diameter of the crankshaft main journal from the larger inside diameter of the main cap, you should get 0.002 inch. If the number is too small or too large, you'll need to order bearings in oversize or undersize increments (typically + 0.001, + 0.002, - 0.001, and - 0.002 sizes).

Rod bearing clearance is measured in a similar way to the main bearing clearance, but you'll want to check the concentricity of the rod's big end at several places before test-fitting the bearings. Once you verify a consistent ID for the rod journal (sans bearing shells), fit the bearing shells to the rod and rod cap. It's important to distinguish between upper and lower bearing shells, which are called out (yellow arrows) by a small embossed stamp with "U" or "L" for upper and lower.

Once again, use an outside micrometer to measure the diameter of the crankshaft's rod journal and an inside micrometer to measure the inside diameter of the rod's big end with the bearings installed and the cap torqued to spec. (Whether you're using the stock main bolts or an aftermarket ARP stud kit will determine what that is; more on this later). Subtracting the rod journal diameter from the rod inside diameter should yield a rod bearing clearance between 0.002 and 0.0025 (ours specced out at 0.0025 inch). IMM says it's only necessary to check one main bearing and one rod bearing to verify that the parts are as advertised, but if you've got time we say it wouldn't hurt to check them all.

MMX's Max Effort SC cam is designed specifically for 392ci Hemis and is optimized for centrifugal blower applications like the popular ProCharger P-1SC . Ground by COMP and sold by MMX, the Max Effort SC VVT cam specs out at 224/236 degrees duration (at 0.050-inch lift), a 114-degree LSA, and 0.598/0.595 inches of valve lift (intake lobe center is 111 degrees). The long exhaust lobe provides the blow-down that's necessary when you have boost; a wide LSA puts the grind on the street-friendly, torque-heavy side. This cam should be used with a COMP 5761 VVT cam-phaser lock-out kit , which MMX supplies as part of their cam kit. After you inspect the cam, lube the lobes with engine oil before installing. Our factory cam bearings were deemed good by IMM. Torque the four T30 Torx bolts of the camshaft thrust plate (yellow arrow) to 106 in-lb. We're pairing our MMX Max-Effort cam to a set of PSI 1511 beehive springs with a rated 130 lbs of seat force (1.800-inch installed height) and 370 lbs of open force (0.625-inch lift, max).

You'll have the choice of reusing the BGE 392's factory piston oil squirters or piston-squirter block-offs from Stanke Motorsports (yellow arrow, inset). Stanke Motorsports specializes in all kinds of cool third-gen Hemi engine parts and we'll be looking at a lot more from them in future stories, but these billet aluminum squirter block-offs are just $45. These reduce the amount of oil around the crankshaft and windage in the oil pan, but at our power level with the amount of heat being produced, MMX recommends that the factory squirters be reused. It's important to check the squirter's clearance with aftermarket pistons; MMX recommends slightly enlarging the squirter's fastener hole which allows the squirter to be rotated counterclockwise a few degrees out of range of potential interference with the piston boss and skirt. Keep an eye on this clearance as you install the pistons and make the necessary adjustments. Torque the squirters' 10mm fasteners to 16 ft-lb after applying a thread-locking compound.

In preparation for laying in the crankshaft, insert the upper main bearing shells into the mains, and give them a helping of assembly lube (yellow arrow) to protect them upon initial start-up. As mentioned previously, at our power target, an ARP main stud kit is considered by the top Hemi engine builders to be essential for long life. Hand-thread the ARP studs into the block and note that the longest stud is designed to anchor the oil pump pick-up once the mains are torqued down. This stud must be placed in the No. 3 main (center) position on the passenger side.

Before laying in the crank, inspect it again, wipe it clean, and apply ample assembly lube in the main bearing shells. If we may indulge in some shameless Mopar partisanship: The factory 392 crankshaft is forged steel, a huge gift from the factory that can handle upwards of 1,200 hp. You won't find anything like this hiding in any junkyard GM LS engine, nor will you find any LS block close to 6.4 liters made of high-nickel alloy like the BGE 392 Hemi block. Both the BGE 392 block and crankshaft forging are the same units that go into the Hellcat Hemi with the only difference being that the BGE's stroke is longer at 3.72 inches (versus the Hellcat's 3.578 inches).

Before installing the main caps, insert the thrust bearings in the center (No. 3) mains. These crescent-shaped units are embossed "R" and "F" for rear and front (inset) and can only slip in from one side. In most cases, the original thrust bearings are cool to reuse if they show no wear. We've seen these last for a quarter-million miles with no signs of wear but new units from Mahle Clevite (part No. TW-611S , $9.99) are available. The oil grooves (not shown) will face the crankshaft cheek.

The 392 Hemi's main caps go on next, and by now you'll finally feel like you're building an engine. The upper halves of the Calico premium coated main bearings (installed in the block earlier) have an oil groove facing the crank surface while the main cap bearing shells do not. The Hemi's cross-bolted main caps are made of billet steel; they're stamped at the factory with their position and have an arrow cast into them indicating their orientation, so it's almost impossible to put them in wrong. Since the caps are mated to their mains from the factory during initial machining, getting them out of order can spell serious damage. Installing the main cap bearing shells is straightforward: After orienting the locating tab, snap them into place, coat them with a smear of engine oil, and slide the caps onto the studs.

The 392's billet main caps are a precision fit so you'll need to incrementally walk them down, alternating between the ends of each cap with a speed wrench, then remove the nuts to apply assembly lube before torquing. Stock main bolts can be used up to around 700 hp, but they can't be reused more than once because they lose their ability to stretch. For stock bolts, torque the mains first to 20 ft-lb in a spiral sequence starting in the center, then go over them again with an additional 90 degrees of twist. Then, torque the cross bolts to 21 ft-lb. If you're upgrading to the ARP main stud kit, use the same spiral torque sequence from the center, torquing the mains to 100 ft-lb. The ARP side bolts are torqued to 25 ft-lb.

In preparation for the timing chain and degreeing the cam, install the COMP VVT cam-phaser lock-out. This kit includes the lock-out chock, set nut, and installation tool. Before taking anything apart, read the instructions carefully; failure to do so can result in the tensioning spring coming unwound, which will be impossible to reattach correctly. 1) Identify this specific spring retainer pin adjacent to the large wedge-shaped window in the front of the VVT drum. 2) Flip the cam gear over, note which of the five Torx screws this pin corresponds to, and mark it (we wrote the word "no" next to it)—this is the one fastener that you will not be removing down the line. 3) Flip the cam gear over and locate the indicated pin in the center of this hole on the VVT drum. 4) Slip the small fingers of the COMP tool on either side of this pin, then tighten the adjustment screw until the tool lifts the spring off the retaining pin. 5) You can observe the VVT spring being lifted off the retaining pin in this view.

Remove all the Torx screws from the VVT cover plate except the one you marked. Crack loose the one you marked, but do not remove it. Slide the cover plate off to reveal the VVT pressure vanes. Put some thread-locking compound on the included set-nut, thread it into the lock-out chock, and drop the lock-out chock into the VVT pressure cavity opposite the stamped hash mark on the cam gear. Tighten the lock nut on the lock-out chock to spread it enough to lock it in place. (It may not tighten enough—if it doesn't, it may produce a slight rattle when the engine is operating.) Slide the VVT cover back in place and reinstall the four cover plate screws. Make sure that the long screw goes back in its original hole (yellow arrows). 

This split image shows how the crankshaft timing gear "dot" lines up with the single chain link having the rectangular icon facing outward (yellow arrow, at left). The right side shows how the cast-in slot mark on the camshaft gear (yellow arrow, right) lines up between the pair of timing chain links that have two consecutive rectangular icons. Unlike a small-block Chevy, these marks do not align at 12 o'clock and 6 o'clock, but at 12 o'clock and 5 o'clock. When installing the timing chain assembly with the block right-side up, the crankshaft's timing gear keyway will be oriented at roughly 2 o'clock.

Unlike a small-block Chevy timing chain, the third-gen Hemi uses a cast-aluminum timing chain guide and a black plastic timing chain tensioner; attach the aluminum guide to the block first, followed by the tensioner, which is a hinged thermoplastic piece with an integral spring and cylinder. Fasteners should be torqued to 250 inch-lb. Hold the swing arm on the tensioner away from the chain by inserting a small pin while compressing the spring (IMM used an Allen key). Once the cam bolt is snugged onto the cam gear, remove the pin from the tensioner to place pressure on the chain. You can use the stock single keyway crankshaft gear, or if you need some incremental adjustment, Stanke Motorsports offers a five-keyway gear for VVT Hemis here ($250) with additional keyways for -2, -4, +2, and +4 degrees of advance or retard (inset).

Mock up the Molnar forged rods with the Mahle PowerPak pistons and slide the wrist pins in. You'll want to place each piston/rod assembly into a vice to hold it steady while you snap a spiral lock into the retaining groove at each end of the pin boss using an awl (inset photo). Then use a pair of piston-ring-expander pliers to install the rings. It's a good idea to clock the ring gaps of the top and second ring opposite from each other to improve cylinder sealing. You may consider using a specialty piston vice like this one here from Proform ($716.99), but as IMM's Brian Hafliger demonstrates, an ordinary vice and some careful handling works fine. There isn't any good substitute for a good set of piston ring expander pliers, so invest in one like this OTC unit from Summit ($16.99).

Begin the piston installation by thoroughly cleaning the bores with solvent then follow this with a coating of engine oil, spreading it around each bore with a gloved hand. Use a ring compressor and a piston knocker (you can get away with using the handle of an ordinary hammer) to carefully tap the piston into the bore. Orient the piston with the exhaust notch down and the crank's rod journal away from the bore so you don't accidentally knock a divot in your rod journal with the big end of the rod.

The Molnar rod caps are held in place with ARP 2000 rod bolts, which we torqued using the stretch method. After applying a dab of ARP assembly lube to the threads, snug the bolts down until they bottom out. Do not torque them hard yet; use ARP's rod bolt stretch micrometer on the ARP cap bolt, zeroing the indicator to set a baseline (right). A glance at the stretch chart provided by ARP says these 7/16 x 1.600-inch bolts need between 0.0060- and 0.0064-inch of stretch to produce the correct amount of clamp load, which is produced by approximately 30 ft-lb of torque plus another 60 degrees. 

You're going to need an accurate torque wrench to assemble engines, and if you haven't picked one up yet, we suggest you take a look at Summit's unit which has a range of 10-150 ft-lb (part No. SUM-907060 , $29.99). The ARP rod bolt stretch micrometer is also available from Summit here for $175.99. After torquing the ARP 2000 rod bolts to 30 ft-lb and then turning them another 60 degrees, you should get the indicated 0.006 to 0.0064-inch of stretch, verified on the stretch gauge (right). Brian Hafliger has done this a few times over the years and using ARP's assembly lube (note that lubricity has a huge bearing on clamp load) he's discovered that 72 ft-lb produces the required amount of stretch with these bolts.

You may choose to degree in your cam after installing the number-one piston/rod assembly, or after all eight are done, but it's critical that you do it before completing the top end of the engine. Rotate the No. 1 piston to TDC, attach the degree wheel to the crankshaft, set up a wire pointer that is attached to the block indexing it to zero degrees on the degree wheel, and position the magnetic dial indicator on the fire deck so the translating pushrod sits in the intake lifter pocket at the proper geometry. With the dial indicator zeroed out at TDC, rotate the crankshaft slowly through the cam's full rotation, noting the valve opening and closing events and their position on the degree wheel. The intake valve events should correlate with your cam card; our cam card's intake centerline was 111 degrees and our actual measurement was very close at 110.5 degrees.

We've still got a couple of things to do to our short-block, like install the oil pump and rear main seal assembly, but it's ready to get a coat of Hemi orange engine paint before moving on to the cylinder heads, valvetrain, and induction. We priced a couple of forged 392ci short-blocks similar to ours (but without a camshaft or timing gear) and found that turnkey assembled prices start around $5,700 and go up from there for one specced similar to ours (these quotes run higher if no core is provided). Over the course of planning our Junkyard 392, we were highly impressed with Modern Muscle Xtreme. When you're spending this kind of cash for parts, it's imperative that you get solid advice. MMX has the experts on hand and really knows the third-gen Hemi with a familiarity that is breathtaking and refreshing. We don't usually comment too much about customer service at HOT ROD, but we need to give big props to MMX for this—the edge here can really make a difference in your next Hemi build.