502 Chevy Big Block Buildup - Generation VI Gorilla Motor: Part 2

In the first installment (April '04) of Sport Truck's 502-cid crate-motor buildup series, we gathered baseline dyno numbers on our test mule's big-block Chevy at Westech Performance Group in Mira Loma, California. After a few good pulls of the stock GM Performance Parts ZZ502 mill, we added some easy-to-install parts from MSD, Comp Cams, Edelbrock, and Demon Carburetion. These upgrades gave the engine a 37hp, 54-lb-ft-of-torque shot in the arm to further this engine's performance. Those upgrades were mild to say the least, using off-the-shelf parts that most readers could install at home. This time around, we're stepping up our program and moving toward our ultimate goal of building a powerhouse big-block Chevy engine that'll run on today's available pump gas.

The Parts
Power is all about airflow. Packing as much air into the engine's combustion chambers as possible, adding a dose of fuel, and throwing a spark on it is the recipe for a big bang and big power. The limiting factor of most engines, and especially our crate motor, is the flow characteristics of the cylinder heads. Now, we could've taken the factory GM Performance Parts heads to a cylinder-head-porting specialist and spent a large chunk of time and money in making them perform better, but we chose an easier route. We called Air Flow Research because it recently developed a completely new line of high-performance aluminum cylinder heads that outflow our current heads. Tony Mamo, head of Product Design for AFR, recommended 315cc CNC-ported Magnum cylinder heads.

The Magnum heads represent a giant leap in cylinder-head design and technology. The heads are available in sizes ranging from 305cc to the big-daddy 357cc CNC-ported behemoths, depending on which CNC program you choose. All the heads feature Tony's unique "heart-shaped" combustion-chamber design, with the differences between them being port size, runner volume, and valve diameter. The combustion chamber's unique shape is Tony's answer to unshrouding the valves for increased airflow; they are available in 119cc and 121cc volumes as cast or CNC-finished versions. The valve placement in the head differs from factory designs because AFR has rolled the valve angles 2 degrees toward the port openings to improve the angle of flow from the valve to the port. Because of the nontraditional valve angle, standard stud girdles won't work on these heads; however, AFR will have its own line available in the future. One great feature that all the heads share is the standard 0.750-inch-thick head deck, which enables these heads to be angle- or flat-milled and still retain their integrity while closing the chamber volumes to as small as 110 cc.

The basic package includes a competition five-angle valve job, stainless-steel 2.25-inch intake valves, and 1.88-inch exhaust valves. Roller dual-valve springs are standard and will provide 240 pounds of spring pressure on the seat. They're good for as much as 0.750 inches of lift. Chrome-moly retainers, valve locks, and seals are included, as are hardened shims and valve seats. The heads are also fit with bronze valve guides, 7/16-inch rocker studs and guideplates, and all standard accessory holes are predrilled and tapped.

When ordering a set of Magnum heads, you'll have many options to choose from to build the perfect head for your application. Valves are available in both stainless-steel and titanium materials, in sizes ranging from 1.60 to 2.30 inches. According to Tony, "These heads are perfect for a nitrous or blower motor that'll generate high cylinder pressures." It's a strong head indeed, and we plan to take full advantage of these flexible performing heads later on.

Our particular heads were flat-milled to mimic the original GMPP head's 110cc chamber volume and retain the original 9.6:1 compression ratio of the engine. Our heads were also outfitted with AFR's tulip-shaped valves (a $40 upgrade), which are good for an additional 10-15 cfm of airflow, depending on where the lift is measured. On smaller-displacement applications, AFR recommends maintaining an intake/ exhaust ratio of 70-80 percent to prevent overscavenging the engine. The techs at AFR will help you choose the proper port volume, combustion-chamber size, and valve diameter.

A head swap alone will not...        read full caption A head swap alone will not build much more power unless we address the timing of events that happen inside the engine while it runs. The camshaft is responsible for coordinating the movement of the valvetrain in relation to the rotation of the crankshaft, so picking the right cam can yield a big boost in power. This time around, we'll be going with a larger, more aggressive mechanical roller bumpstick from Comp Cams. Our last camshaft was a fairly mild street grind, which worked well with its surrounding parts, but would be insufficient with the high-flow characteristics of our AFR heads. The new camshaft was designed by none other than cam guru Billy Godbold, head of design for Comp Cams. This cam has a gross valve lift of 0.661 inches on the intake side and 0.668 inches on the exhaust. Although we'll have to relash the valves from time to time, this cam will help to make excellent power, and the valve springs won't prematurely wear out. Duration at 0.50 inches of lift is 254 on the intake and 260 on the exhaust side, with a 112-degree lobe separation.	The rest of the valvetrain...        read full caption The rest of the valvetrain also came from the Comp Cams catalog and included custom-length pushrods, Endure-X Roller lifters, and 1.73-ratio aluminum rocker arms.
To feed the hungry beast,...        read full caption To feed the hungry beast, we went with an Edelbrock Victor JR intake manifold, which AFR port-matched to the new heads. The Victor JR intake has increased-length runner dividers and a smaller plenum, which helps boost power between 3,000 and 7,000 rpm. Although not visible in the photos, the intake manifold was set in place atop AFR's own intake gaskets, which are sized to perfectly outline the intake ports in the heads.	Since the heads were flat-milled...        read full caption Since the heads were flat-milled prior to being installed, we had to mill the endrails of the intake manifold off to allow the intake to bolt in place with the correct port alignment and without the end rails bottoming out on the engine block. ARP bolts were used to lock the manifold down. A Holley 950HP-series carburetor replaced the 850-cfm Demon carb we tested in the first installment of this series. The 950HP Race-series carb works great right out of the box with minor jetting changes and features power-valve blowout protection, four-corner idle circuits, and Dominator-style dual-feed fuel bowls. All HP carbs are wet-flow-tested and calibrated with screw-in air bleeds and dual 30cc accelerator pumps.	The only changes made to the...        read full caption The only changes made to the bottom end of the motor were in the form of an 11-quart-capacity Moroso oil pan, a high-volume/high-flow oil pump, and a TCI Rattler dampener. The pan features a built-in windage tray to prevent oil from accumulating on the crankshaft as it rotates. The pump is blueprinted to provide maximum oil pressure throughout the powerband and keep cavitation in check. This Moroso pan also provides a larger, more controlled supply of oil compared with the stock pan, thanks to its trap door, baffles, and built-in windage tray. The pan is also equipped with bungs for an oil-temperature sending unit and drain plug. Your application may look different from the one shown.
The Install After making...        read full caption The Install After making 20 pulls on the Superflow dyno at Westech Performance Group to ascertain the engine's maximum performance, we hauled it home to disassemble and inspect the innards. The top end of the engine was unbolted, beginning with the intake and carb assembly, then the factory cylinder heads were removed.	Next, the old valvetrain assembly...        read full caption Next, the old valvetrain assembly was removed and replaced with our new units from Comp Cams. Scott Parkhurst of Popular Hot Rodding magazine was kind enough to stop by and degree in the new camshaft. We wound up installing it straight up per Comp's instructions.
FelPro cylinder head gaskets...        read full caption FelPro cylinder head gaskets were called into play, and then we were ready to bolt on the new AFR heads. These high-performance racing head gaskets are of standard thickness and feature a metal crush-ring around each bore hole for increased sealing strength	The new heads were installed...        read full caption The new heads were installed using ARP head bolts, which were torqued to 75 lb-ft.	ARP bolts were again used...        read full caption ARP bolts were again used to secure the new Edelbrock VR JR Air Gap intake manifold.
The manifold was port-matched...        read full caption The manifold was port-matched by AFR to the cylinder heads, taking advantage of the head's unique intake-port shape. The stock ports on the intake line up fairly well, but we didn't want to leave any power on the table by not port-matching the components.	In the external-accessories...        read full caption In the external-accessories department, a TCI Rattler crankshaft dampener was chosen to keep a lid on harmonics, and a mini high-torque starter motor from Powermaster turns over the engine. The Rattler absorbs the amplitudes of vibrations and angle of crankshaft twist.	The Rattler is effective throughout...        read full caption The Rattler is effective throughout the entire operating range of the engine and will extend bearing life. It's also lighter than most other units on the market and contains no fluids, elastomers, or friction materials that may require maintenance.
We hauled the engine back...        read full caption We hauled the engine back to Westech Performance Group for its next round of torture-testing on the Superflow dyno, where technician Steve Brul made sure the engine was tuned for maximum effort. After a few pulls to make sure everything was in good working order, Steve played with the engine's ignition timing, valve lash, and carburetor jetting.	The final tune-up, which netted...        read full caption The final tune-up, which netted the best numbers of the day, was as follows: 1-inch carb spacer Jets: 82/82 Total ignition timing: 34.5 degrees Valve lash: intake 0.010/exhaust 0.016 Exhaust: 2-inch primary tube headers with 3-1/2-inch collectors and Flowmaster mufflers

The Payoff
To say that this motor is impressive would be the understatement of the year. We were literally blown away at this mill's ability to produce gobs of power on 91-octane fuel. With a compression ratio of just 9.75:1 and off-the-shelf parts that can easily be installed by nearly any home mechanic, this engine is a forgiving recipe that will definitely haul the mail in your pickup. Dyno-testing showed that this engine continuously made more than 700 hp all day long and had several peak runs reaching near 740 hp. The really impressive spec, though, is this motor's extremely flat torque curve. From 4,000 to 6,400 rpm, the engine never made less than 612 lb-ft of torque.

Max power = 739 at 6,400 rpm
Max torque = 669.9 at 4,700 rpm