GM Performance Parts 502 Torque Motor Buildup

131 9809 Torque Motor Buildup Engine And Valve Cover

An engine buildup usually targets a specific need: A trail 4x4 needs an engine that will idle all day long and produce torque down low; a mud truck needs lots of horsepower, and it's fine if the engine has to turn a high rpm to make that power; and a tow rig needs lots of power but with low compression to avoid detonation. It's rare when one engine can fit all these requirements.

At least that's what we thought at the onset of a recent 502 engine buildup. But then we looked at what we were starting with and what is available for a big-block Chevrolet engine, and realized that this is it-the omni-engine.

131 9809 Torque Motor Buildup Completed Engine Blue

Background
GM Performance Parts offers 502s in a few varieties. The off-road 502 truck-conversion engine (PN 12371054) makes 338 hp and 512 lb-ft of torque, and the Gen VI H.O. 502 (PN 24502620) makes 450 hp and 550 lb-ft of torque. An H.O. 502 comes with better cylinder heads and camshaft than the truck-conversion engine. It's also more complete than the conversion engine, including an intake manifold, a water pump, and a flexplate. From this engine, you can build anything from a brute-torque daily driver and off-road engine up to a full-blown competition powerplant-all using the same short-block. This allows you to start now with a complete crate engine and build it over time to fit your desires.

GM Performance Parts also offers two engine kits; the 502/502 base engine kit (PN 12371204) starts with an assembled short-block and includes oval-port heads, valvetrain, and valve covers to make 502 hp and 567 lb-ft of torque, while the 502/502 premium kit also includes the intake, carb, water pump, starter, and ignition system. You can also buy just a 502 short-block (PN 24502619).

131 9809 Torque Motor Buildup Engine Crate

We began our powerful adventure with a new Gen VI H.O. 502 from GM Performance Parts. It comes with iron, rectangle-port heads, an aluminum dual-plane intake, a damper, a water pump, and a flexplate. Inside the short-block is a steel crank and forged pistons along with a hydraulic roller cam (211/230 degrees at 0.050 and 0.510/0.540-inch lift).

We began our powerful adventure with a new Gen VI H.O. 502 from GM Performance Parts. It c

Our Plan
We started with a GM Performance Parts Gen VI H.O. 502 and made bolt-on changes to produce two more potent-power combinations. With its massive displacement, the H.O. 502 engine is a darn impressive engine right out of the crate-a fact we verified by dyno-testing one fresh from the GM parts counter. The GM Performance Parts catalog (which is available at your local dealer or can be downloaded from the GM Performance Parts Web site free of charge) claims the H.O. makes 450 hp at 5,250 rpm and 550 lb-ft of torque at 3,500 rpm.

Leafing through the GM Performance Parts catalog revealed a pair of rectangular-port aluminum heads (in addition to oval-port heads) and the roller camshaft used in the 502/502 engines. While traditional thinking is that oval-port heads make better low-end power at the expense of a few horsepower, we decided to try the new rectangle-port heads (in fact, all three cylinder heads used on this engine were rectangle-port) with the 502/502 cam. For this combination, we used an Edelbrock Performer RPM, a Holley 750 double-pumper, Crane Hi-6 ignition, 2-inch Hedman headers, and 2 1/2-inch exhaust with Flowmaster 50-Series, three-chamber mufflers.

If this version isn't calling your name, there's still more power you can build with the stock short-block. We experimented with a pair of iron Merlin VR Race cylinder heads from World Products and a Crane Street Roller camshaft and then added other components that become necessary at higher-power levels, such as an Edelbrock 454-R intake, a Jones Performance carburetor, Manley valves, and a Milodon oil pan. The result was plenty of power to turn 44s or anything smaller through even the worst gumbo. Even though this last variation of the 502 is more of a competition engine, the parts were chosen so that it could live on the street and still run on pump gas.

The Outcome
You can stuff a big-block Chevy into nearly any 4x4 (we've even seen them in Jeeps), and we've shown just three versions of this venerable engine. Because of its displacement, a very mild 502 will produce gobs of torque that any off-road vehicle can use. And, whether you know up front or decide after a few years of use, the same 502 can be built to meet nearly any power need.

Kevin McClelland and John Wilson fit the 502 to Flowmaster's dyno and dressed it with a 750-cfm Holley double-pumper carb and 2-inch primary-tube Hedman headers, which were connected to 2 1/2-inch exhaust with Flowmaster 50-Series mufflers. We used a stock HEI from GM Performance Parts and Crane's FireWire spark-plug wires. The engine was broken in using Quaker State nondetergent 30W oil, which was changed to Quaker State 4x4 20W50 before any tests were started. We verified the catalog's power claims: The engine produced peaks of 446.7 hp at 5,250 rpm and 547.9 lb-ft of torque at 3,250 rpm.
Kevin McClelland and John Wilson fit the 502 to Flowmaster's dyno and dressed it with a 75
McClelland removed the heads, intake, and cam to create version two of our 502 using GM Performance Parts rectangle-port aluminum heads and the 502/502 roller camshaft. In this photo you can see the small dome on the 502 pistons.
McClelland removed the heads, intake, and cam to create version two of our 502 using GM Pe
If you've ever messed with cam buttons, then you will really appreciate the simplicity of the cam thrust plates. These are used on Gen VI blocks and limit the front movement of the camshaft. The H.O. 502 comes with a single-roller timing set, which we retained for all of our testing.
If you've ever messed with cam buttons, then you will really appreciate the simplicity of

The 502/502 camshaft uses the stock lifter spider and guides. We used Fel-Pro gaskets and ARP fasteners to put the engine back together. This power-level engine would be fine with ARP head bolts, but we knew we'd be pushing the limit with our final version of this engine, so we opted for the studs. The Signature Series aluminum rectangle-port heads have 2.19-inch intake valves and 1.88-inch exhaust valves. The intake ports are between 300 and 315 cc, and the exhaust ports are 110 cc. The combustion chambers are 118 cc.
The 502/502 camshaft uses the stock lifter spider and guides. We used Fel-Pro gaskets and
The net lash (nonadjustable) stock valvetrain won't work with a 502/502 cam, so we used 1.7:1 roller rockers from GM Performance Parts and Crane rocker studs. Our engine had a 0.022-inch deck height, 4cc dome pistons, 0.041-inch-thick head gaskets, and 118cc chamber heads for a compression ratio of 8.69:1. That's slightly less than the crate-version compression ratio of 8.75:1, and the aluminum heads dissipate more heat than iron, both of which result in a slight loss of power. Machining the heads to reduce the combustion chamber would bring up the compression ratio.
The net lash (nonadjustable) stock valvetrain won't work with a 502/502 cam, so we used 1.
For the next two versions of the 502, we added a Crane Fireball Hi-6 ignition system to the dyno. As power levels increase, the air/fuel ratio becomes more difficult for stock ignitions to fully ignite, making a quality aftermarket system a necessity. The Crane ignition works with the HEI distributor and includes such features as a built-in, adjustable rev-limiter and optional timing-retard controls.
For the next two versions of the 502, we added a Crane Fireball Hi-6 ignition system to th

Version two received the same Hedman headers and Flowmaster mufflers used in version one, but we added an Edelbrock Performer RPM manifold and 850 Holley double-pumper. We also slid on a set of GM Performance Parts cast-aluminum Chevrolet-script valve covers. We switched MaxJet jets in the Holley until we achieved the best power with 91s in all four corners and 32 degrees of total timing. This combination produced peaks of 501.3 hp at 5,500 rpm and 565.5 lb-ft of torque at 3,250, and it still idled under 900 rpm.
Version two received the same Hedman headers and Flowmaster mufflers used in version one,
Now it's time to get serious. Sure, the first two versions made great power, but you haven't seen anything yet. The short-block is plenty strong to support power levels higher than 600 hp, but it's generally accepted that the top ring-end gap needs to be increased from 0.024 inch to 0.028 inch. Otherwise, the higher heat from more power will cause the ends to butt, which will damage the cylinder walls. While we had the rods and pistons out, we threw in a new set of Clevite 77 rod and main bearings and Hi-Tech one-piece cam bearings from Number 1 Performance.
Now it's time to get serious. Sure, the first two versions made great power, but you haven
The aluminum heads were good, but in order to make a significant jump in power, we needed a pair of heads with serious flow characteristics. We chose iron World Products Merlin VR Race heads, which are very affordable considering the quality. The combustion chambers are 119 cc out of the box, but we had RPM Engines & Machine mill them 0.030 inch to bring the chambers down to 112 cc. This resulted in a compression ratio of 9.12:1.
The aluminum heads were good, but in order to make a significant jump in power, we needed

McClelland flowbenched the Merlins and found that the ports flowed pretty well out of the box, but we felt they could be improved upon, so we had Brian Jenson at RPM work on the ports as well as clean up the combustion chambers. RPM's experience at porting high-flow cylinder heads and attention to detail showed in the final power numbers we achieved with this 502.
McClelland flowbenched the Merlins and found that the ports flowed pretty well out of the
Brad Reich at RPM refinished the valveseats and blended them into the newly shaped ports. The SuperFlow flowbench showed 324 cfm at 0.600-inch lift and 346 at 0.700 on the intake and 281 cfm at 0.600-inch lift and 295 at 0.700 on the exhaust after the porting. Starting with good cylinder heads and having professional work such as this done is one of the keys to making big power from an engine.
Brad Reich at RPM refinished the valveseats and blended them into the newly shaped ports.
Even for this top-dog version of the 502, we're only making a few changes to the basic engine as delivered. We selected a Crane Street Roller (SR) camshaft (foreground) with 262/270 degrees of duration at 0.050- and 0.636-inch lift. The cam has an iron distributor gear so you can run a standard gear on your distributor. The ramps on the cam lobes are designed to give the highest rate of lift without damaging the lifters on the street. Steeper ramps mean more power, but they also place a higher load on the lifters, thus reducing lifter life.
Even for this top-dog version of the 502, we're only making a few changes to the basic eng

Race-roller camshafts wear out the lifters and valvesprings because of the incredible rate of lift in addition to the large amounts of lift. The Crane SR camshafts lessen this and require a slightly softer valvespring combination for much better durability. We had the Merlins outfitted with Manley Severe-Duty 2.250-inch intake and 1.880-inch exhaust valves and Crane valvesprings, keepers, and retainers.
Race-roller camshafts wear out the lifters and valvesprings because of the incredible rate
On the bottom end, oil control is an issue, so we installed a Milodon oil pan and pick-up tube. Oil pans are different between the Mark IV and the later Gen V and VI blocks. This Milodon pan has baffles to control oil movement, notched rails to accommodate up to a 4.5-inch stroke with aluminum rods, and a 7-quart capacity. We also used Milodon oil-pan studs to make removing the pan easier for maintenance of the bottom end.
On the bottom end, oil control is an issue, so we installed a Milodon oil pan and pick-up
We used Crane pushrods and guide plates and Crane 1.70:1 Gold roller rockers. The rockers feature an extruded body for maximum strength. The chrome-moly 3/8-inch-diameter pushrods measured 9.250-inch on the exhaust and 8.250-inch on the intakes. On an engine of this nature, you must check valvetrain geometry and you may need custom-length pushrods.
We used Crane pushrods and guide plates and Crane 1.70:1 Gold roller rockers. The rockers

Because of the high-lift camshaft, either shaft-mounted rockers, which take quite a bit of time and patience to set up correctly on the heads, or valvetrain stabilizers, also called stud girdles, are necessary. We chose the Crane Quick-Lock valvetrain stabilizers. One drawback to these is that they often affect valve lash so you have to set the lash, tighten the girdles, recheck the lash, and reset it if necessary. Another is that they don't fit under short valve covers; however, they do fit under the Chevrolet-script valve covers.
Because of the high-lift camshaft, either shaft-mounted rockers, which take quite a bit of
For version three of the 502, we switched from an Edelbrock Performer RPM (left) to a Victor 454-R. The Victor has the runner dimensions and volume necessary to transport the copious amounts of air and fuel the large heads and engine can now use. McClelland ported the intake to clean the runners and gasket-matched the ports to the Fel-Pro intake gaskets and cylinder heads.
For version three of the 502, we switched from an Edelbrock Performer RPM (left) to a Vict
The 454-R has a Holley Dominator flange, so we departed from the 850 double-pumper for a pair of Jones Performance Dominators. The first one we tried was a 750, and then we switched to a 1050. Both carburetors exhibited good throttle response, with the 1050 producing 20.6 more horsepower and 3.7 more lb-ft of torque, as shown in dyno charts Version Three, Parts I and II.
The 454-R has a Holley Dominator flange, so we departed from the 850 double-pumper for a p