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GM Performance Parts 502 Torque Motor Buildup

Engine And Valve Cover
Cole Quinnell | Writer
Posted September 1, 1998

Three ways to build a 502

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.

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).

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.


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Flowmaster Inc.
Santa Rosa, CA 95401
Crane Cams
Daytona Beach, FL 32117
Comp Cams
Memphis, TN 38118
World Products
Ronkonkoma, NY 11779
GM Performance Parts
Detroit, MI 48232
JET Performance Products
Huntington Beach , CA
Number 1 Performance
Quaker State
RPM Engines & Machines
Ronhert Park, CA 94928
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