Stroked Six

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By Steve Magnante

Photography: Steve Magnante

Even though the 440ci Mopar has been out of production for more than 20 years, there has never been more interest in this potent mill than there is We hooked up with veteran speed merchant Joe Jill at Superior Automotive in Garden Grove, California, and followed along as he, and engine-man Sam Garcia put the coals to a big wedge. In the process, they bumped displacement to 500 ci, tailored the compression ratio to a pump-gas friendly 10.3:1, capped it off with aftermarket aluminum heads, and plopped a nostalgic, yet very capable, Six-Pak induction on top of the hairy thing.

Repeated trial fitment of the reciprocating assembly will ensure adequate clearance for the connecting rods.

The best part about this Mopar's resurgence is that you don't have to sacrifice your first-born child to make big power. The forged stroker crank, billet-steel rods, and forged pistons used in this 500-inch buildup are new premium parts available from Superior Automotive in kit form for a mere 53,125 (including rings, bearings, and precision balancing). Add aluminum Indy 440-SRA heads and a hot flat-tappet cam like we've done here, and this creature will belt out nearly 600 horsepower and 600 Ib-ft of torque all night long. So get on board and start turning those wrenches; there's a Six-Pak coming to suck up your town!

The 440 was produced from 1966-78, and all of them can withstand 800-plus horsepower—although the blocks manufactured from 1976-78 were lighter, thin-wall castings. While this may sound like a bonus, the cylinder material is so thin that Chrysler recommends a maximum safe overbore of just 0.020 inch. We have seen the cylinders in these later blocks overbored beyond this margin but only after sonic checking revealed sufficient wall thickness.

In order to clear the rear main seal support, the rearmost studs must be shortened ½ inch. Further, 12-point nuts are mandatory, a peculiarity specific to Mopar big-blocks running main stud kits. For maximum accuracy, Jill torques all main-cap fasteners in 10-pound increments to a maximum of 100 Ib-ft.

Many blocks cast after 1973 feature figure-eight—shaped coolant passages in their deck surfaces, which allow greater coolant flow but weaken the area of the deck adjacent to the head bolt holes. When the bolts are torqued, they actually pull this surface up and distort the cylinder wall approximately 0.0005 inch. This distortion can have a negative impact on ring seal but is only worth worrying about when going to the nth degree. Pre-'73 blocks have smaller, round coolant passages in the decks that do not contribute to bore distortion in this fashion. To determine the vintage of a 440 block, look for the date cast into the passenger side of the cylinder bank.

The Indy oil line kit taps into the main galleys at the rear of the block to provide pressurized lubrication to the rocker arms via the drilled passages. The passages go through the rear rocker-shaft stands and then into the hollow rocker shafts where oil is dispersed to the rocker arms and valve tips.

The basis for our project is a 1970 casting that was pressure tested and Magnafluxed prior to modification. To make room for the increased stroke, Jill ground clearance notches at the base of each cylinder bore and mocked-up the lower-end assembly several times to ensure a minimum clearance of 0.100 inch between the connecting rods and cylinder block. To make perfect alignment between the cam and lifters and to correct for factory lifter-bore machining errors, the block was mounted in a BHJ lifter-truing fixture, and the bores were offset reamed to an oversize dimension. Then bronze bushings were pressed into the bores and honed to factory-blueprint dimensions. Besides centering the lifters directly over the lobes of the camshaft, this process also enhances lower-end oil supply by eliminating lubricant bleed-off to the lifters, so that more is available to the main and rod bearings. When this operation is performed on a motor with hydraulic tappets, the bronze inserts must be drilled to reconnect them to the oil galley, but in this case, where solid lifters will be employed, these holes are not needed.

Jill discovered that the number-three main cap, which handles all thrust loads, was binding on the crankshaft. The bore diameter was sufficient, but the factory drilled main bolt holes were not perfectly perpendicular. Although not a problem with stock bolts, after the installation of larger shank studs, this inaccuracy forced the cap to shift when the studs were tightened, pinching the crankshaft thrust surface. Clearance was restored by simply enlarging the main-cap bolt holes an additional 0.010 inch.

Even with two-bolt main caps, the 440's deep-skirt crankcase configuration offers a very rugged lower end. For added reliability, the stock bolts were replaced by 1/2-inch ARP studs (PN 140-5401), which are claimed to increase clamping ability by 60 percent. Further block prep included align-honing the main bearing saddles and overboring the cylinders 0.040 inch for a finished diameter of 4.360 inch. Although taking the bores to 0.060 inch would yield a tad more displacement, Jill wisely regards the wall material region as sacred. Once it's gone, it can't be replaced. Minimizing overboring allows room for repairs and makes the cylinders stiffer for a better ring seal. The stock oil-pickup-tube hole was enlarged from 3\8-inch to 1\2-diameter to accommodate a Milodon extended oil-pickup tube PN 18330), which supplies the high-volume Milodon external oil pump (PN 18790). The rest of the oiling system was composed of a 7-quart Milodon low-pro-file pan (PN 31010) and a Mopar Performance windage tray (PN P4120998).

Oh, the glory of massive cubic inches. Replacing the stock 3.75-inch stroke with a Mopar Performance 4.15-inch arm brings 60 more of 'em to the orgy. Forged from high-quality 1053 steel, the MP stroker crank (PN 5249208) features a Hemi-spec eight-bolt flange and fully radiused fillets to eliminate stress risers. Conveniently, it is also prebalanced, requiring only some touch-up balancing work before it's ready.

A stroker crank increases the load on the connecting rods. The consensus is that a 500-inch motor at 5,500 rpm stresses the rods equal to that of a 440-incher at 7,000 rpm. While stock forged rods can handle plenty of abuse, using them inside a stroker that'll pull 6,500 rpm is risky business. For complete peace of mind, Jill employed forged Manley/Ray Barton rods (6.760 inches, PN 14274). These babies weigh 20 percent less than the stockers (for better throttle response) and come with polished beams and high-quality ARP bolts. For increased reliability and the coveted SFI rating, Jill used a neutral-balanced Pro Street Performance Products balancer (PN 64279).

A custom BHJ drill fixture replicates the factory blueprint lifter-bore positioning for corrections to the block. Here, the reamer enlarges a lifter bore. Note the bronze bushings at left.

A complement of JE custom-forged pistons with raised pin bores and lull-floating 0.990-inch tool steel piston pins secured by spiral locks accommodates the added stroke. Despite their dished and heavily notched crowns, these slugs yield a healthy 10.3:1 compression ratio when used with the 73cc Indy 440-SRA cylinder heads. Their abbreviated skirt design reduces weight and provides ample clearance with the counterweights and cam when the crankshaft is at BDC. The Childs & Albert ring pack consists of a 1\16-inch file-to-fit dura-moly top rings (0.020-inch end gap) and 1\16-inch second rings (0.025-inch end gap), which allow for a quick break-in against the Sunnen #625-grit cylinder-bore finish Jill prefers for street-oriented powerplants. The Clevite 77 tri-metal rod bearings (PN CB-527HD) are set at 0.0022, and the prechamfered, fully grooved main bearings (PN MS896P) for use with radiused crankshafts are set at 0.0025 inch.

All 1968 and newer cylinder heads are capable of supporting 1 hp per cubic inch with nothing more than a basic valve job and a little bowl work. They were all factory-equipped with generous 2.08-inch intake and 1.74-inch exhaust valves, virtually identical port configurations, and similarly sized open combustion chambers (ranging from 82 to 86 cc). The point is, don't break your back or your budget looking for the "good" castings. The 906, 346, and 452 heads are ready to rock. However, if the budget allows, take advantage of aftermarket light alloy heads; they work even better than their iron cousins. With 500 inches fighting for air, enhanced flow is mandatory. For this project, Jill specified Indy 440-SRA aluminum castings.

For less than $3,200, Superior supplies the innards that transform your 440 into a 500-cube tire shredder. Rings, bearings, and final balance work are included. The forged JE pistons are custom-made to suit each application.

Indy street heads feature raised ports with larger volume, which lengthen and maximize the critical short-turn radius for better breathing. They are fitted with 2.14-inch in-take and 1.81-inch exhaust valves. Jill spent six hours bowl-blending, port-smoothing, and deck-milling to bring them even closer to perfection. The hardened valve seats, bronze valve-guide inserts, and stainless steel Indy valves ensure hassle-free motoring on pump gas. Head gaskets are Mopar Performance composite (PN 452 9455) with 0.038-inch compressed thickness).

The friction generated by stock-type "scrubber" rocker arms against the valve tips allows some of the motion to push sideways on the valve stems. This accelerates guide wear and precipitates harmful vacuum leaks that let oil get past the seals and enter the intake ports during the intake stroke. Oil in the combustion chamber can cause severe detonation. Crane billet-aluminum roller rockers (PN 64790-1) reduce friction at the valve tip and the side-loading that occurs between valve stem and guide. Like stock stamped-steel Chrysler rockers, the billet replacements feature a 1.5:1 ratio. For this street-oriented application, Jill saw no need to compromise the stock valvetrain geometry with higher-ratio rockers.

Even though the 440 has a large cylinder case, the heads of the inboard rod bolts must be relieved for clearance. Removal of material has no impact on reliability.

After checking its events with a degree wheel, Jill installed the the CamMotion flat-tappet solid-lifter camshaft (PN S2564-261 1-10), which is ground with 0.547-inch intake and 0.554-inch exhaust lift and 257/262-degrees duration. It goes in the motor straight up. This cam works with 125/350-pound double valvesprings and hardened-steel spring cups; chrome-moly retainers; and hardened, single groove locks; all of which are standard on the Indy 440-SRA cylinder head. Pushrods are Indy %-inch chrome moly that measure 9.75 inches. The added length is necessary to accommodate the higher-than-stock rocker-arm location of the Indy heads.

The owner of this 500-incher wanted an induction system that was nostalgic, practical, and had the ability to make plenty of power. Superior supplied an original '69J4-'70 Edelbrock-sourced aluminum Six-Pak setup (later units were cast iron) and a trio of Holley carburetors (1,350 cfm maximum). To simplify the tuning process, Jill thinks of the Six-Pak as a vacuum secondary carburetor with four secondary throttle bores. The 350cfm center carburetor is equipped with jets, power valve, metering block, and accelerator pump; The Crane roller-rocker kit (PN 64790-1) comes with special heavy-wall rocker shafts that resist flexing in the presence of high valvespring pressure. the 500cfm outer carbs have only diaphragms and metering plates. While prepping the Six-Pak for this buildup, Jill took the hot cam and big cubes into account and enlarged both of the main metering orifices of the front carb to 0.089 inch and installed #63 jets in the center carb; then he opened the orifices in the rear carb to 0.093 inch (driver side) and 0.086 inch (passenger side).

A Hemi racer since 1964, Jill knows how to make a Chrysler big-block live. In stock form, the number-three thrust bearing needs additional oil, especially when coupled to a manual transmission and high-effort pressure plate. Adding a third oil groove and enlarging the two existing grooves provides extra lubrication.

Still on a nostalgic bent, the customer specified a stock Chrysler breakerless electronic distributor for its original looks and 7,000rpm ability when used in conjunction with a Mopar Performance chrome ECU (PN P4120534) and lightweight advance springs.

Left: Despite the windage tray, power-robbing oil still ropes around the crankshaft. To offset this parasitic drag, Superior provides optional knife-edged crankshaft counterweights that act like the bow of a ship parting water. Right: After a few hours with a grinder, the intake and exhaust ports showed a vast improvement. Smooth, as-cast finish of combustion chambers negated the need for cleanup work.

Jill's shop removed casting irregularities and blended the transitions between the valve seats and throat openings.

Indy heads feature angled spark plugs, which are said to enhance rapid flame propagation. Intake and exhaust ports are raised 1/2-inch higher than stock and should be checked for interference between the exhaust headers and the chassis.

Jill applied red Loctite to the Cloyes double-roller timing-set bolts and torqued them to 30 Ib-ft. Safety wire ensures their permanence. Since the lobes of a flat-tappet camshaft are ground with a small taper, which gently preloads it to the rear of the block during operation, a cam thrust button is not needed.

A dial indicator measures piston-to-valve clearance in the number-one cylinder with the piston at top dead center and the valve at maximum lift. Clearance was a safe 0.200 inch.

Jill used Mopar-specific Holley 2300 series carburetors because most universal-fit Holley 2BBL carbs lack provisions for vacuum diaphragms and have no idle screws in the baseplate. Holley still manufactures the correct carbs; the restoration aftermarket can supply everything else.

The Crane roller-rocker kit (PN 64790-1) comes with special heavy-wall rocker shafts that resist flexing in the presence of high valvespring pressure.

To accommodate the raised ports in the Indy head, a ½-inch aluminum spacer closes the gap between the cylinder block and the steel Fel-Pro valley pan (PN 1215), which comes with four thin-paper gaskets (two per side).

This story was originally published in the February 1999 issue of HOT ROD. MOTORTREND and HOT ROD's rich magazine history and legacy dating back to 1948 is something highly valued by its longtime readers, and that's why we've invested deeply to make the content available to you in a modern and accessible format. In the interest of transparency, these magazine articles are presented as originally published, without modification, and may contain content that does not reflect the company's contemporary values and standards.