Chevy Engine Block - Cutweight Horsepower

Swapping a Cast-Iron Block for an Aluminum One on a Chevy Small-Block V-8

Mark Stielow Sep 1, 2006 0 Comment(s)
Sucp_0609_01_z Chevy_engine_block_swap Aluminum_block 1/22

Upgrading an existing cast-iron block-based engine to an aluminum engine block is a great way to reduce the weight on the front area of a vehicle. It makes it easier for the vehicle to accelerate, brake and corner, adds to the cool factor, and possibly can lead to an increase in power output. The aluminum engine block requires preparation and assembly methods that are a little different from a cast-iron block, but you're about to learn a lot of those details here. So get ready to go light.

Sucp_0609_02_z Chevy_engine_block_swap Crank_main_journal 2/22

An aluminum block "expands" twice as much as an iron block (because aluminum has twice the expansion as cast-iron), so the crank main journal clearances are set at or under 0.002 inch (versus the 0.0025 to 0.0027-inch range for an iron block). This tight clearance when the engine is cold demands quality oil flow at startup, and also that you warm up the engine thoroughly before beating on it. As per the Bow-Tie info card, the main webs were torqued to 65 lb-ft on the vertical bolts, 60 lb-ft on the splayed bolts, and 45 lb-ft on the two little bolts at the front main cap.

Setup: This engine is out of Mark Stielow's Thrasher '69 Camaro Pro Touring ride that he built back in 1999, and will be going into Jim Mulvey's Camaro in place of a supercharged big-block. The improvement in overall weight and front/rear bias is going to be dramatic. The original small-block Chevy engine made 520 hp, 510 lb-ft of torque based on a 406ci cast-iron block with unported 23-degree cylinder heads, open-plane intake, and an ACCEL fuel injection system.

Stielow has decided to upgrade the engine with a GM Performance Parts Bow-Tie aluminum block, Dart CNC-machined 18-degree cylinder heads, and some new valvetrain components to take advantage of the new high-flowing heads. While he drove the decision to go lightweight and improve the flow, the experts at Wheel to Wheel Powertrain (W2W), in Madison Heights, Michigan, weighed in on the details of upgrading the existing engine.

Assembly: As far as foundation choices go, it doesn't get much better than the GM Performance Parts Bow-Tie aluminum block. It is a beautiful piece of equipment with a near-surgical appearance in the cast and machined areas. To add to the mystique, the block is shipped in a special wooden crate with paperwork on the sonic testing so you can "see" the quality of the construction. The aluminum Bow-Tie block has pressed-in cast-iron cylinder liners that can be machined to a maximum diameter of 4.185 inches. But this engine was originally built with 4.125-inch bores and the original Arias pistons look practically brand-new, so the block is being machined to 4.125-inch bores.

Sucp_0609_05_z Chevy_engine_block_swap Main_webs 3/22

An aluminum block has thicker main webs than an iron block, which requires the crank counterweight throws to be machined 0.100 inch at the outer edge, and tapered back to the bearing surface. This requires rebalancing the crank-which you have to do for the piston-and-rod combination anyway. Just make sure to do the backcut before the initial balancing.

Head Games: The aluminum, 18-degree Dart cylinder heads just looked too good to not try. The reference to the "18 degrees" is the amount the valves are "angled" from the centerline of the cylinder bore. While the Gen I small-block Chevy V-8 originally came out with 23-degree valve angles, over the years racers have determined that reducing that angle allowed them to run smaller combustion chambers, improve the angle of the intake port, and generally make more power. The 18-degree angle was pioneered by racers in NASCAR and remains as a common upgrade in performance small-blocks.

Making the change to 18-degree heads requires a new intake, or at least serious machining of an intake built for a 23-degree head (which really isn't recommended, as the intake port shape will not take full advantage of the 18-degree ports). Also, a "spacer" will usually need to be added to the "China Wall" area at the front and rear of the engine. Valvetrain changes will abound to achieve "correct" valve geometry. You'll probably want to replace the camshaft to get the most out of the new heads. Expect to make changes to the fuel and spark application, as these heads usually flow better than any 23-degree head you've run.

The real improvement came once this engine was bolted into Jim Mulvey's Camaro. Stielow reported to us that you could feel the change the lightweight block and high-flowing cylinder heads made to the power and nose weight of the vehicle. The resulting faster acceleration and a more "flickable" performance makes all the work required to make this change worth it.

Sucp_0609_07_z Chevy_engine_block_swap Main_oil_passage_plugs 4/22

The First-Generation Chevy small-block V-8 design has many press-in plugs in the iron block, but on the aluminum Bow-Tie version, these Allen plugs are used. When final installing, these main oil passage plugs should have their threads coated with Loctite 592 thread sealer/lock and installed to quarter-turn past hand-tight. The threaded holes between each lifter set are drainbacks that require stands to prevent high amounts of oil pouring on the cam and crank.

Sucp_0609_08_z Chevy_engine_block_swap Pistons 5/22

This shot gives an idea of what it looks like to run 18-degree cylinder heads-the oversize, straight-on intake port requires the intake valve lifter pushrod seat to be offset 0.150 inch to create room for the oversized intake ports. The Arias dished pistons are asymmetrical to exactly match each cylinder's chamber shape-so make sure you mate them up to the correct hole.

Sucp_0609_09_z Chevy_engine_block_swap Combustion_chamber_view 6/22

The CNC-machined combustion chamber on the Dart (PN#14172121) cylinder heads offer fully CNC-machined surfaces with 2.15 intake/1.625 exhaust stainless steel valves. Notice how the valves have been machined on the backside of the head to remove material-this reduces weight and allows for a slightly smaller combustion chamber to maximize "squish" area on the sides of the chamber (that results in power).

Sucp_0609_10_z Chevy_engine_block_swap Lifter_bores 7/22

The offset Crower Super Duty hydraulic roller lifters are set into the lifter bores of the Bow-Tie block after being soaked in a bucket of oil for a while (to fill the cavity in the hydraulic lifter). Before each pushrod is installed, W2W adds some #3 high-pressure lube to the tip of the pushrod.

Sucp_0609_11_z Chevy_engine_block_swap Main_and_head_studs 8/22

The Bow-Tie block can be ordered with a full set of head and main studs, or you can get a set from ARP. These ARP 7/16-inch thread (one end fine, the other end coarse thread) head studs are being installed to 100 in/lbs. This torque is essentially "hand-tight" and can be accomplished by using the "two open-end wrench" method as shown here. There are two head studs in the center of the head that "neck down" from 7/16 inch to 3/8 inch (they go between the Siamesed intake ports). W2W suggests you use the head gasket bolt holes as a guide to where to put these studs in the block. Notice the Fel-Pro head gasket installed after wiping the block and cylinder head surfaces off with lacquer thinner.

Sucp_0609_12_z Chevy_engine_block_swap Intake_port 9/22

The Dart CNC-machined intake port is a work of art. Notice how the valve-stem guide is molded into the overall shape of the port (arrow)-that helps to make power. Also, the light vertical lines (arrows) are from W2W's "port-matching" activities. They measured the intake manifold port width is equal to or less than the port width of the cylinder head-this keeps flow at a maximum through that area.

Sucp_0609_13_z Chevy_engine_block_swap Pushrod 10/22

The length of the 3/8-inch-thick Manley pushrods were determined with the use of the T&D-provided valvetrain geometry tool. This tool shows when the rocker stands are shimmed to the proper height with the correct length the pushrod.

Sucp_0609_14_z Chevy_engine_block_swap Edelbrock_intake 11/22

An aluminum Edelbrock 18-degree Victor Jr. intake manifold has been heavily chiseled on by Wilson Manifolds for maximum flow. Notice the diamond in middle (arrow) with sloping angles to the port entrances and the holes in the carb mounting plate to "pin" the Wilson carb spacer for exact placement. Cool.

Sucp_0609_15_z Chevy_engine_block_swap Intake_valve 12/22

Wilson further prepped the intake manifold for maximum fuel-injected power by machining holes for the fuel injectors at 15 degrees from vertical and welding the mounting bungs into each port (finger). This positioning showers the backside of the intake valve with the majority of the fuel spray. Note: the slick Wilson fuel rail mounts and the mounts welded to the intake to hold the rails in place on the Accel injectors.

Sucp_0609_16_z Chevy_engine_block_swap Dart_cylinder_heads 13/22

When making major changes to the cylinder head valve angle when building an engine, a major issue to deal with is the angle "stackup" that show up at the intake manifold to cylinder head and block mounting face. To address this issue, the Fel-Pro intake gaskets are taped to the fully assembled Dart heads and the intake set in place. Notice the installed timing chain cover (the cam is installed and degree'd) and ATI harmonic balancer.

Sucp_0609_17_z Chevy_engine_block_swap Cylinder_heads 14/22

This is where the experience of an engine builder is invaluable. The Dart cylinder head castings sit approximately 0.250 inch high off the 'china wall' of the Bow-Tie block and require an aluminum spacer to be bolted to the block (after drilling and tapping 0.250 inch threaded holes in the "China Wall") with countersunk Allen bolts. Notice the Manley drainback oil stands installed the lifter valley (arrow), the massive Bow-Tie cast into the front of the block and the gold anodized Allen plug that is sealing off the dry-sump oiling passage that is part of this very capable Bow-Tie block.

Sucp_0609_18_z Chevy_engine_block_swap Electronic_fuel_injection 15/22

The electronic fuel injection and ignition systems are operated by an ACCEL Gen VII DFI system. An ACCEL Universal Wiring Kit (PN#77021), which features an unterminated wiring harness, were used to make a custom-fit harness. This kit includes all the connectors and terminals you will need to build a harness. Mike Brown, at Wires and Pliers, used this kit as a starter to whip up one of his ultra-custom engine harnesses for a very clean appearance. He also integrated an ACCEL wide-band O2 system into the harness at the same time.

Sucp_0609_19_z Chevy_engine_block_swap Throttle_body 16/22

The Accel billet throttle body is similar to a carburetor with the two small primary throttle blades and large secondary throttle blade. Notice the Accel dual sync distributor (PN#77100) trigger and MSD spark plug wires. The dual sync distributor gives the Engine Control Module (ECM) the cam sync signal to enable sequential fuel injection. Like most electronic fuel injection engine buildups, an adjustable distributor slip collar was required to get the distributor gear properly lined up with the cam gear for the computer to "find" top dead center on the engine.

Sucp_0609_20_z Chevy_engine_block_swap Valve_lash_adjustment 17/22

Since this engine is equipped with a roller cam, there really isn't any "break-in" procedure. It was just warmed up and then shutdown so the valve lash could be set at 0.024 inch on all rockers. Then the calibration work was begun. This started with just getting the engine to idle properly, then focused on getting max power from a run.

Sucp_0609_21_z Chevy_engine_block_swap Motor_calibration 18/22

The calibration work that is performed on the dyno is usually focused on wide-open throttle (WOT) applications under load. These are difficult to perform with the engine in the car (there just isn't enough road, traction or speed limit to give it justice). The calibration work performed in the vehicle encompasses everything else: idle quality, driveability, deceleration, cold start, hot soak, etc.

The Bow-Tie block can be ordered with many different features, since this is the block required for use in all GM-bodied NASCAR vehicles. A customer can order one from any GM dealer, but you'll probably want to find the closest GM Performance Parts Authorized Center (go to www.gmgoodwrench.com) to get some guidance from the pros. Stielow likes to work with GM Performance Parts dealer Scoggin-Dickey Chevrolet, in Lubbock, Texas.

All Bow-Tie blocks come with some high-end features, like screw-in coolant plugs (shown, left) and billet rear cam covers with inset O-rings (shown, right), priority main oiling systems (practically a must for real performance engines) and more.

More important to the enthusiast is that Bow-Tie blocks are available in either cast-iron or aluminum, set up for dry- or wet-sump oiling systems, and with various main bearing diameters (the NASCAR Cup boys have experimented with small journal sizes to reduce frictional losses). There are also a few different deck heights, and the option of purchasing a rough bored block so your local machine shop finish bores and hones. Why are there so many variations? Because there are so many ideas on how to build the "ideal" performance small-block V-8.

In general, some classes, like Nextel Cup, have rules that require a cast-iron engine block-so the racers want cast-iron as the block material. Again, Nextel Cup allows the expensive and complex dry-sump oiling systems, so the racers want a block that is already designed, cast, and machined to take full advantage of the dry-sump system-and the Bow-Tie block is set up for that. The different bearing diameters and deck heights are requested by these same engine builders, as the rules don't specify exactly what they need to be-so the racers are always experimenting with different setups in the quest for more power, durability, and...well, any advantage they can find.

Notes from test: Fuel rail pressure was set at 60 psi, engine coolant temperature averaged 173 degrees F, oil pressure averaged 61 psi and oil temperature averaged 178 degrees F during dyno run

RPMTrq (lb-ft)Power (hp)A/F Ratio (left side)Maniold Vacuum
300039022313.470.2
310039923613.380.2
320040824913.440.2
330041626113.490.27
340042327413.590.27
350042628413.410.3
360042228913.040.3
370041829512.870.3
380042030412.850.3
390042031213.040.33
400042332212.080.4
410042933513.080.4
420043434713.070.4
430043935913.10.49
440044537213.140.5
450045138613.220.5
460045940213.240.59
470046641713.250.65
480047243213.190.69
490047544413.070.7
500048145812.940.7
5100488474130.7
520049048512.980.79
530049550013.030.85
5400BF51413.020.89
550049952413.040.9
560049953213.030.9
570049653913.010.99
580049657412.851
590049355412.841.09
600049056012.831.1
610048456212.811.18
620048056612.831.2
630047557012.681.2
640047257512.591.3
6500467BF12.471.3

Block: GM Performance Parts aluminum Bow-Tie
Details: 4.125-inch bores, 9.020-inch deck height, pressed in cylinder liners, set up for 3.500 mains and a wet-sump oiling system

Heads: Dart
Details: Fully CNC-machined cylinder head to achieve 59cc chamber volume, set up for 2.050/1.600-inch-diameter stainless, backcut valves with a valve-stem diameter of 11/32 inch, valve angle of 18-degree, poured from 356 virgin aluminum. Rocker stands machined to locate T&D shaft rocker stands at the proper height. Heads machined to attain 0.305- and 0.310-inch clearance of intake and exhaust valves at max lift from pistons at Top Dead Center (TDC) location of 0.013-inch proud of the deck. Compression ratio is 10.53:1.

Crank: Scat
Details: 4130 steel Ultralite Scat crank, 3.750-inch machined counterweights to clear aluminum webbing on all mains (see photo), riding on Clevite 909H series bearings-used because its half-groove design manages oil "bleedoff" better, which is critical in an aluminum block

Rods: Scat
Details: 6.000-inch steel, full floating pin in bushing, I-beam design riding on Speed Pro 7100 CH bearings

Pistons: Arias
Details: Forged aluminum, flat-top except for slight dish (equaling 15cc volume), 0.43, 0.43, 1/8-inch Speed Pro ring pack with gaps filed 0.020 inch - top, 0.25 inch - second, 0.030 inch - oil ring rail. Checked for size and condition, cleaned, lubed, and reinstalled.

Valvetrain Comp Cams
Details: Roller camshaft (PN#12-000-9, grind CS 4873/4874 SR 112 0) with 0.603/0.609-inch valve lift (with 1.6:1 rockers) on 236/242 degree duration at 0.050-inch lift on 108 degree lobe centers and a lobe separation of 112 degrees. Lobe lift of 0.377 and 0.381 int/exh.
Cam held in place with a COMP "wear plate" (PN#201). A COMP double-roller timing chain set (PN#3100) and cover (PN#208) spin the cam and Comp valvesprings (PN#26089-16) control the valve action. The valvesprings were shimmed to an installed height of 1.900 inch. The installed height pressure is 280 lb/in and the "over the nose" (at the top of the 0.600 inch lobe) pressure is 600 lb/in (at 1.300 inches high). Coil-bind is at 1.200 inch of valvespring height with the COMP titanium (Ti) retainers, locks, and ID-centered cups (COMP PN#4785-16) under the valvesprings. Crower roller lifters and tiebars were used.

T&D
Details: 1.6:1 ratio shaft-mount, billet rocker system (PN#2050) with intake 0.465-inch offset and exhaust 0.170-inch offset

Manley
Details: 3/8-inch-diameter, 8.550-inch-long pushrods (PN#25855-16)

Oiling System: Moroso
Details: '69 Camaro road-race pan, PN#21900, Moroso standard volume pump and pickup, pns 22100 and 24170 held in place with ARP oil pump stud (PN#230-7001) and actuated by Melling oil pump pushrod (PN#15-77) Intake - Wilson-prepped Edelbrock Aluminum, single-plane (PN#2994) with a 6.40-inch manifold height to clear the hood. Hand-ported by Wilson Manifolds for maximum flow. Wilson also welded in fuel-injector bungs and stands for their aluminum fuel rails and provided spacer for throttle body (PN#74202S3).

Fuel Injection: ACCEL
Details: Gen VII sequential fuel injection system. 36 lb/hr injectors, 1,200-cfm throttle body,

Fasteners: ARP
Details: head studs (PN#2344336), balancer bolt (PN#134-2503), cam bolt kit (PN#300-1001), distributor stud (PN#430-1701), intake (PN#434-2101), valve cover (PN#400-7613)

Gaskets: Fel Pro R.A.C.E. set (PN#2702) that comes with 4.200-inch gasket bore, 0.041-inch-thick head gasket

Custom components
Spacer to fill area between block China Wall and intake. Wheel to Wheel Powertrain created this aluminum piece and bolted it to the block with countersunk Allen head bolts.

Engine Assembled by: Wheel to Wheel Powertrain (W2W), Madison Height, Michigan

Sources

Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
Dart Machinery
Troy, MI 48084
248-362-1188
www.dartheads.com
Wilson Manifolds
Ft. Lauderdale, FL
954-771-6216
http://www.wilsonmanifolds.com
Wheel to Wheel Powertrain
Madison Heights, AK 48071
248-589-1190
http://www.w2wpowertrain.com
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