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Build a 740hp Big-Block Chevy in Your Driveway

Posted in How To on September 20, 2004
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The crate engine craze has elevated horsepower to new levels, which the Average Joe mechanic can attain simply by whipping out the old credit card and making a phone call. On a daily basis, we find advertisements for big-block crate engines producing 500, 600, and even 700 hp on pump gasoline available at your local station. Of course, this is all fine and dandy if that's all the power you're after. But what if you want a few more ponies? What if you have to have the most powerful engine in the neighborhood? What if you're inclined to do the job yourself?

OR has done the homework and come up with a recipe of parts that will bolt onto a Generation VI GM Performance Parts ZZ502 crate engine to build more than 700 hp when fed just 91-octane fuel. Not only do the parts bolt onto the engine, but we even have the basic tune-up figured out to make this brute of a big-block scream once it's in your truck.

This article isn't meant to show you every step involved in assembling a complete engine, but it'll give you the pertinent information needed should you feel froggy enough to tackle the job of completing the long-block yourself. Aside from port-matching the intake manifold to the cylinder heads, this engine combination can be assembled at home with basic tools. It all starts with a pre-assembled Gen. VI 502 partial engine assembly (short-block) from GMPP. This short-block (part number 24502619) features forged pistons, a forged steel crank, forged connecting rods with 7/16-inch bolts, a redesigned front timing cover, and one-piece front and rear main bearing seals. It's an excellent basis for a high-performance truck engine, and thanks to its 4.47-inch bore and 4-inch stroke, will breathe well with aftermarket cylinder heads. One thing to note here is that this Gen. VI block does not have a provision for a mechanical fuel pump, so you'll need to add an electric pump to your truck if it doesn't already have one.

Now that we've established our jumping-off point with the short-block, let's add our power parts. The short-block will arrive at your door already assembled with an oil pan and also includes a flexplate for your automatic transmission.

The Parts
Power is all about airflow. Packing as much air into the engine's combustion chambers, adding a dose of fuel, and throwing a spark on it is the recipe for big bang and big power. We placed a call to Air

Flow Research because it recently developed a completely new line of high-performance aluminum cylinder heads with excellent flow characteristics. Tony Mamo, head of product design for AFR, recommended the 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 305 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 the port size, runner volumes, and valve diameter. The combustion chamber's unique shape is Tony's answer to unshroud the valves for increased airflow and is 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, but 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, a feature 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 valvesprings are standard, will give 240 pounds of spring pressure on the seat, and are 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 fitted with bronze valveguides, 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 will generate high-cylinder pressure." A perfectly strong head, indeed, and we plan to take full advantage of these flexible performing heads later on.

Our particular heads were flat-milled to bring the 119cc combustion chambers down to 110 cc of volume, which yielded a 9.6:1 compression ratio with the pistons that came in the short-block. 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 over-scavenging the engine. The techs at AFR will help you choose the proper port volume, combustion-chamber size, and valve diameter.

The camshaft is responsible for coordinating the movement of the valvetrain in relation to the rotation of the crankshaft, and picking the right cam can yield a big boost in power. The specs for the cam are: duration at 0.050 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 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, 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. Because the heads were flat-milled prior to being installed onto the engine, we also had to mill the end rails 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. The Holley 950 HP 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 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 9.6:1 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 606 lb-ft of torque.

Dyno Information 502-cid BBC
RPMPowerTorque
4,000467.0 612.7
4,500565.0 658.9
5,000636.0 666.7
5,500687.0 656.2
6,000727.0 636.8
6,500738.1 596.4
 
Max power=739.0 @ 6,400 rpm
Max torque=669.9 @ 4,700 rpm

Options
The factory oil pan, oil pump, and dampener are fine for most applications. Should you feel the need for some addition insurance, you can add a higher-capacity oil pan. The only changes made to the bottom end of this 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, and 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 versus 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.

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The Install

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